US20120313895A1 - Touch screen - Google Patents

Abstract

A method for determining the location of an object on a touch panel is provided. Initially, a pulse of terahertz radiation is transmitted through a touch panel, which formed of a dielectric material such that the pulse generates a evanescent field in a region adjacent to a touch surface of the touch panel. A reflected pulse is generated by an object located within the region adjacent to the touch surface of the touch panel, and a position of the object on the touch surface of the touch panel is triangulated at least in part from the reflected pulse.

Description

TECHNICAL FIELD
• The invention relates generally to a touch screen and, more particularly, to a terahertz-enabled touch screen.
BACKGROUND
• Touch screens have become ubiquitous, being included in mobile devices (i.e., phones) and other devices (i.e., tablet computers). There is however difficulty in engineering larger displays (such as for “black boards). Resistive and capacitive touch panels for large scale applications can be expensive and “power hungry,” while projector based solutions suffer from occlusion. Thus, there is a need for a touch sensitive system that is scalable.
• Some examples of conventional circuits and systems are: Williams, “Filling the THz Gap,” doi:10.1088/0034-4885/69/2/R01; Heydari et al., “Low-Power mm-Wave Components up to 104 GHz in 90 nm CMOS,”ISSCC2007, pp. 200-201, February 2007, San Francisco, Calif.; LaRocca et al., “Millimeter-Wave CMOS Digital Controlled Artificial Dielectric Differential Mode Transmission Lines for Reconfigurable ICs,” IEEE MTT-S IMS, 2008; Scheir et al., “A 52 GHz Phased-Array Receiver Front-End in 90 nm Digital CMOS”JSSC December2008, pp. 2651-2659; Straayer et al. “A Multi-Path Gated Ring Oscillator TDC With First-Order Noise Shaping,”IEEE J. of Solid State Circuits, Vol. 44, No. 4, April 2009, pp. 1089-1098; Huang, “Injection-Locked Oscillators with High-Order-Division Operation for Microwave/Millimeter-wave Signal Generation,” Dissertation, Oct. 9, 2007; Cohen et al., “A bidirectional TX/RX four element phased-array at 60 HGz with RF-IF conversion block in 90 nm CMOS processes,” 2009IEEE Radio Freq. Integrated Circuits Symposium, pp. 207-210; Koh et al., “A Millimeter-Wave (40-65 GHz) 16-Element Phased-Array Transmitter in 0.18-μm SiGe BiCMOS Technology,”IEEE J. of Solid State Circuits, Vol. 44, No. 5, May 2009, pp. 1498-1509; York et al., “Injection- and Phase-locking Techniques for Beam Control,”IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 11, November 1998, pp. 1920-1929; Buckwalter et al., “An Integrated Subharmonic Coupled-Oscillator Scheme for a 60-GHz Phased Array Transmitter,”IEEE Transactions on Microwave Theory and Techniques, Vol. 54, No. 12, December 2006, pp. 4271-4280; PCT Publ. No. WO2009028718; and U.S. Pat. No. 3,673,327.
SUMMARY
• An embodiment of the present invention, accordingly, provides a method. The method comprises transmitting a pulse of terahertz radiation through a touch panel formed of a dielectric material such that the pulse generates a evanescent field in a region adjacent to a touch surface of the touch panel; generating a reflected pulse from an object located within the region adjacent to the touch surface of the touch panel; and triangulating a position of the object on the touch surface of the touch panel at least in part from the reflected pulse.
• In accordance with an embodiment of the present invention, the step of triangulating further comprises: receiving the reflected pulse by a first receiver and a second receiver that are separated from one another by a distance; and calculating the position of the object based at least in part on a first elapsed time between transmission and reception at the first receiver, a second elapsed time between transmission and reception at the second receiver, and the distance.
• In accordance with an embodiment of the present invention, the reflected pulse further comprises a first reflected pulse, and wherein the step of triangulating further comprises: generating a second reflected pulse from a reflector included in the touch panel; receiving the first and second reflected pulses by a receiver; and calculating the position of the objected from the first and second reflected pulses.
• In accordance with an embodiment of the present invention, the reflector is located along the periphery of the touch panel.
• In accordance with an embodiment of the present invention, the pulse further comprises a first pulse, and wherein the reflected pulse further comprises a first reflected pulse, and wherein the first pulse is transmitted by a first transceiver, and wherein the method further comprises: transmitting a second pulse of terahertz radiation through a touch panel by a second transceiver; and generating a second reflected pulse from an object located within the region adjacent to the touch surface of the touch panel.
• In accordance with an embodiment of the present invention, the step of triangulating further comprises triangulating the location of the object on the touch surface of the touch panel from the first and second reflected pulses.
• In accordance with an embodiment of the present invention, an apparatus is provided. The apparatus comprises a touch panel formed of a dielectric material that is configured to carry terahertz radiation and having a touch surface; and a touch controller that is optically coupled to touch panel, wherein the touch controller is configured to transmit a pulse of terahertz radiation through the touch panel so as to generate a evanescent field in a region adjacent to the touch surface, and wherein the touch controller is configured to receive a reflected pulse that is generated by an object located within the region, and wherein the touch controller is configured to triangulate a position of the object on the touch surface at least in part from the reflected pulse.
• In accordance with an embodiment of the present invention, the touch controller further comprises: a signaling circuit that is configured to generate and receive terahertz radiation; and a control circuit that is coupled to the signal circuit.
• In accordance with an embodiment of the present invention, the signaling circuit further comprises: a transceiver; a local oscillator that is coupled to the transceiver; and a receiver circuitry that is coupled to the transceiver.
• In accordance with an embodiment of the present invention, the receiver circuitry further comprises an analog baseband circuit that averages the combined signal for a plurality of sampling periods within a digitization window to generate a plurality of averaged signals and that converts the plurality of averaged signals to a digital signal.
• In accordance with an embodiment of the present invention, the analog baseband circuit further comprises: a clock circuit; a low noise amplifier (LNA) that is coupled to the summing circuit; an averager that is coupled to the LNA and the clock circuit; an analog-to-digital converter (ADC) that is coupled to the LNA and the clock circuit; and an output circuit that is coupled to the ADC.
• In accordance with an embodiment of the present invention, the transmitter further comprises: a transmitter that is coupled to the local oscillator; and a plurality of receivers that are spaced apart from one another and that are each coupled to the receiver circuitry.
• In accordance with an embodiment of the present invention, the touch panel further comprises a reflector.
• In accordance with an embodiment of the present invention, a method is provided. The method comprises transmitting a pulse of terahertz radiation through a touch panel formed of a dielectric material such that the pulse generates a evanescent field in a region adjacent to a touch surface of the touch panel; generating a plurality of reflected pulses, wherein a first reflected pulse is generated by a object located within the region adjacent to the touch surface of the touch panel; and triangulating a position of the object on the touch surface of the touch panel at least in part from the plurality of reflected pulses.
• In accordance with an embodiment of the present invention, the object further comprises a first object, and wherein the position further comprises a first position, and wherein a second reflected pulse of the plurality of reflected pulses is generated by a object located within the region adjacent to the touch surface of the touch panel and at a second location.
• In accordance with an embodiment of the present invention, the step of triangulating further comprises: receiving the plurality of reflected pulses by a first receiver and a second receiver that are separated from one another by a distance; and calculating the position of the object based at least in part on the plurality of reflected pulses.
• In accordance with an embodiment of the present invention, a third reflected pulse of the plurality of reflected pulses is generated by a reflector.
• The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
• FIG. 1 is an example of touch screen system in accordance with an embodiment of the present invention;
• FIG. 2 is diagram an example of a portion of the operation of the system ofFIG. 1;
• FIG. 3 is a cross-sectional diagram ofFIG. 2 along section line I-I;
• FIG. 4 is diagram an example of a portion of the operation of the system ofFIG. 1;
• FIG. 5 is a cross-sectional diagram ofFIG. 2 along section line II-II;
• FIG. 6 is a block diagram of an example of a phased array system that can be employed with the signaling circuit ofFIGS. 1-5;
• FIG. 7 is a block diagram of an example of the local oscillator (LO) ofFIG. 6;
• FIG. 8-11 are block diagrams of examples of the transceivers ofFIG. 6;
• FIG. 12 is a circuit diagram of an example of the multipliers ofFIGS. 8-11;
• FIG. 13 is a circuit diagram of an example of the phase shifters ofFIGS. 8-11;
• FIG. 14 is a circuit diagram of an example of the injection locked voltage controlled oscillator (ILVCO) ofFIGS. 8-11;
• FIG. 15 is a circuit diagram of an example of the power amplifier (PA) and low noise amplifier (LNA) ofFIGS. 8-11;
• FIG. 16 is block diagram of an example of the radiator ofFIGS. 8-11;
• FIG. 17 is a block diagram of the phased array system ofFIG. 6;
• FIGS. 18 and 19 are timing diagrams that depict examples of the operation of the phased array system ofFIG. 6;
• FIG. 20 is a circuit diagram of an example of the switches ofFIG. 6;
• FIG. 21 is a circuit diagram of an example of the analog-to-digital converters (ADCs) ofFIG. 6;
• FIG. 22 is a circuit diagram of the low pass/band pass filter ofFIG. 17;
• FIGS. 23 and 24 are circuit diagrams of an example of a time to digital converter used with the ADCs ofFIG. 6;
• FIG. 25 is a timing diagram depicting an example of the operation of the time to digital converter ofFIGS. 23 and 24;
• FIG. 26 is a circuit diagram of an example of the summing circuit for the receiver circuitry ofFIG. 6;
• FIG. 27 is a diagram of an example of the receiver circuitry ofFIG. 6;
• FIG. 28 is a diagram of an example of the analog baseband circuit ofFIG. 27;
• FIG. 29 is a diagram of an example of the averagers ofFIG. 28,
• FIG. 30 is a diagram of an example of the switched capacitor banks ofFIG. 29; and
• FIGS. 31 and 32 are diagrams demonstrating the operation of the system ofFIG. 6.
DETAILED DESCRIPTION
• Refer now to the drawings wherein depicted elements are, for the sake of clarity, not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.
• This application incorporated by reference co-pending U.S. patent application Ser. No. 12/871,626, entitled “DOWNCONVERSION MIXER,” filed on Aug. 30, 2010; co-pending U.S. patent application Ser. No. 12/878,484, entitled “TERAHERTZ PHASED ARRAY SYSTEM,” filed on Sep. 9, 2010; and co-pending U.S. patent application Ser. No. 12/871,626, entitled “ANALOG BASEBAND SYSTEM FOR A TERAHERTZ PHASED ARRAY SYSTEM,” filed on Apr. 12, 2011.
• Turning toFIG. 1, an example of asystem100 in accordance with an embodiment of the present invention can be seen. As shown, thesystem100 generally comprises atouch panel102,control circuit104, signalingcircuit106, and reflectors107-1 to107-4. Generally, thetouch panel102 is a large panel (i.e., 2 m×2 m) formed of a sheet of dielectric material (such as glass or polyethylene) that is capable of carrying terahertz radiation (which typically has a frequency range between 0.1 THz and 10 THz) and functioning as a dielectric waveguide for this terahertz radiation. Typically, thistouch pane102 can also include a transparent cladding112 (as shown inFIG. 3) located between thetouch panel102 and display (i.e., liquid crystal display or LCD screen). The signaling circuit generally comprises transmission and receiver circuit (i.e., such as the phasedarray system200 detailed below) that is optically coupled to the touch panel so as to transmit and receive terahertz radiation through thetouch panel102. There are a number of configurations that thesignaling circuit106 may have such as a single transceiver (i.e., system200), multiple transceivers, or a signal transmitter with multiple receivers. Thecontrol circuit104 may includes logic or a processor (such as a digital signals processor or DSP) that is configured to calculate object location on the touch surface of thetouch panel102 and to control the signaling circuit. Additionally, reflectors107-1 to107-4 may be optionally included to assist in triangulating an object location and may be included at any position (including the periphery as shown) on thetouch panel102. There may be any number of reflectors, but one likely configuration is to include the reflectors107-1 to107-4 at each corner of thetouch panel102.
• Because terahertz radiation exhibits optical behavior, it can be transmitted through thetouch panel102 in a similar manner infrared radiation being transmitted through an optical fiber. As a result, the terahertz radiation generates an evanescent field in anevanescent field region114 that is adjacent to the touch surface of thetouch panel102. When transmitted through fibers or other transmission media, infrared, visible spectrum, and ultraviolet radiation also generate an evanescent field in an evanescent field region, but this region for infrared, visible spectrum, and ultraviolet radiation is much smaller thanevanescent field region114 because of the frequencies. Thus, because theevanescent field region114 is so much larger, it is much easier for interference within thisregion114 to be detected, which can be seen inFIGS. 2-5.
• In the example shown inFIGS. 2-5, an object an object (i.e., a finger or pointer)110 is located with in theevanescent field region114 at a location on the touch surface of thetouch panel102. When thesigning circuit106 generates apulse108 of terahertz radiation, this transmittedpulse108 propagates through thetouch panel102 and generates an undistortedevanescent field116 withinregion116. When the undistortedevanescent field116 encounters theobject110 that is located withinregion114,evanescent field116 becomes distorted (as shown with the distortedevanescent field120 ofFIG. 5), and a reflectedpulse118 is generated. This reflectedpulse118 then propagates back to thesignaling circuit106. Based at least in part on the reception of this reflectedpulse118, thecontrol circuit104 can triangulate the position of the object on the touch surface of thetouch panel102. Typically, two or more receivers (which are spaced apart from one another) are employed and the time-of-flight (or time elapsed from transmission to reception) along with the spacing between receivers within signalingcircuit106 can be used for triangulation. Alternatively or additionally, reflectors107-1 to107-4 (which have been omitted fromFIGS. 2-5) may be employed to assist in performing triangulation.
• Turning toFIG. 6, a phased array system200 (which can be used as part of signaling circuitry106) can be seen. Thephase array system200 generally comprises aLO202, a phasedarray224, adistribution network226,receiver circuitry228, andcontroller208. The phasedarray224 generally comprises several transceivers204-1 to204-N arranged in an array. Thedistribution network226 generally comprisesamplifiers206 and208-1 to208-N. Additionally the receiver circuitry generally comprises a summingcircuit210, amixer212,amplifier214,filter216, switches218-1 to218-N,variable selector220, and ADCs222-1 to222-N. While a phased array may not be necessary (i.e., asignal transceiver204 may be employed), it may be preferable in order to allow for optical alignment with thetouch panel102. Additionally, detection of a single object (i.e., object110) is shown inFIGS. 2-5, but detection of multiple objects (so-called “multi-touch”) can be performed (which typically uses multiple reflectors to assist in eliminated background noise and more accurately determining the positions for the objects).
• In operation, phased array system200 (which is generally incorporated into an integrated circuit or IC) can generate a short range radar system that operates in the terahertz frequency range (which is generally between 0.1 THz and 10 THz). To accomplish this,local oscillator202 generates a high frequency signal FL01 that is on the order of tens to hundreds of gigahertz (i.e., 40 GHz, 50 GHz, 67 GHz, and 100 GHz.) and a pulse signal TPUSLE. Thedistribution network226 then provides signal FL01 to each of the transceivers204-1 to204-N such that the signals received by each of transceivers104-1 to204-N are substantially in-phase. Acontroller208 provides a control signal toarray224, which phase-adjusts the transceivers204-1 to204-N with respect to one another to direct a beam of terahertz frequency radiation. The transceivers204-1 to204-N can then receive reflected radiation back from a target, which is provided to summingcircuit210. The output of summingcircuit210 is the converted to a digital signal by amixer212,amplifier214,filter216, switches218-1 to218-N,variable selector220, and ADCs222-1 to222-N. Additionally,mixer212 can receive a divided signal from LO202 (i.e., FL01/2 or another synthesized signal) or can be removed (typically for 40 GHtz or less).
• Generally, this phasedarray system200 has several different types of operational modes: pulsed, continuous, and stepped frequency. For a pulsed operational mode, a pulse of terahertz radiation is directed toward a target. The continuous operational mode uses a continuously generated beam, which is generally accomplished by effective “shutting off” the pulse signal TPULSE. Finally, stepped frequency allows to frequency of the terahertz beam to be changed, which can be accomplished by employing a bank of local oscillators (i.e.,202). For the pulsed operational mode, in particular, the range of thesystem200 is governed by the following equation:
• $\begin{array}{cc}R=\sqrt[4]{\sigma \frac{{\mathrm{<figure-callout\; label="PG"\; filenames="US20120313895A1-20121213-D00004.png,US20120313895A1-20121213-D00010.png"\; state="\{\{state\}\}">PG</figure-callout>}}^2\lambda \mathrm{nE}\left(n\right)}{{\left(4\pi \right)}^3\mathrm{kTBF}\left(\frac{S}{N}\right)}},& \left(1\right)\end{array}$
• where:
• • R is distance that can be measured or range;
  • a is the radar cross section of the target (usually not equal to the physical cross section);
  • S/N is single pulse SNR at the intermediate frequency IF filter output (envelope detector input);
  • kTB is the effective incoming noise power in receiver bandwidth B (B≈1/pulsewidth);
  • F is noise figure of the receiver (derived parameter);
  • P is the peak transmitter power;
  • G is the antenna power gain;
  • λ is wavelength of the radiation (i.e., for 200 GHz, ≈1.5 mm);
  • n is number of integrations of pulses in the receiver (multi-pulse averaging); and
  • E(n) is the efficiency of integration.
    For a monolithically integrated, low power IC that includessystem200, this range is generally less than one meter.
• Turning toFIG. 7, an example of theLO202 can be seen in greater detail. Generally, thisLO202 employs a phase locked loop (PLL)326 that generates signals FL01 and FL02 from reference signal REF and employs counter322 andpulse generator324 to produce the pulse signal TPULSE.PLL326 is generally comprised of aphase detector302,charge pump304,low pass filter304,amplifiers310 and312, voltage controlled oscillator (VCO)308, anddividers320,318,316, and314. In operation, thephase detector302 receives a feedback signal fromdivider314 and the reference signal REF, and (along withcharge pump304 and low pass filter306) generates a tuning voltage forVCO308. Typically,VCO308 generates a high frequency signal (i.e., 100 GHz, 67 GHz, 50 GHz, or 40 GHz) which is amplified byamplifiers310 and312, producing signal FL01. Divider320 (which is generally an injection-locked, divide-by-2 frequency divider) receives the output of amplifier to output signal FL02. Signal FL02 is then provided to divider318 (which is generally a divide-by-2 current mode logic divider). The output ofdivider318 is provided to divider316 (which is generally a divide-by-8 current mode logic divider), and the output ofdivider316 is provided to divider314 (which is generally a divide-by-M CMOS divider) to generate the feedback signal. Thecounter322 generates a count signal based on a control signal CNTL and the feedback signal fromdivider314, and the pulse generator234 produces the pulse signal TPULSE based at least in part on the count signal fromcounter322 and the outputs ofdividers318 and320.
• InFIG. 8, an example of one of transceivers202-1 to202-N (referred to as202-A) can be seen in greater detail. As shown, transceiver202-A generally includes a transmit path402-A and a receive path404-A that are each coupled to radiator426 (i.e., antenna). During transmission, phase shifter404 (which is generally controlled by controller230) receives signal FL01 fromLO202 and phase-shifts signal FL01 accordingly. This phase shifted signal is amplified byamplifier408 and multiplied by multiplier410-A (which is typically a multiply-by-3 multiplier) that allows the signal FL01 to be increase to the desired frequency range. For example, if signal FL01 is about 67 GHz, then multiplier410-A would output a signal having a frequency of about 201 GHz. This multiplied signal is provided toILVCO412, which is generally used to compensate for losses from multiplier410-A. Additionally,ILVCO412 receives the pulse signal TPULSE. Power amplifier (PA)414 then amplifies the output ofILVCO412 for transmission throughradiator426. Typically, the pulse widths of pulse signal TPULSE are about 30 ps, 60 ps, or 90 ps when the signal FL01 has a frequency of about 67 GHz. During reception,radiator426 receives a signal, which is amplified byamplifier420. This amplified signal is mixed with a signal having a frequency that is a multiple of signal FL01. Typically, multiplier416 (which is generally a multiply-by-2 multiplier) receives an output fromamplifier408, and the result is amplified byamplifier418 and provided tomixer422. The mixed output is then amplified byamplifier424 and provided to summingcircuit210. Additionally,mixer422 is described in co-pending of U.S. patent application Ser. No. 12/871,626 entitled “DOWNCONVERSION MIXER.”
• Looking toFIG. 9, an alternative configuration for one of transceivers202-1 to202-N (referred to as202-B) can be seen in greater detail. The transmit path402-B is similar to transmit path402-A; however, multiplier410-B has replaced multiplier410-B. Generally, multiplier410-B has a large range than multiplier410-B to accommodate a lower frequency signal FL01. For example, if signal FL01 has a frequency of 50 GHz, then multiplier410-B can be a multiply-by-4 multiplier to generate a signal that is on the order of 200 GHz. Additionally, to accommodate a lower frequency signal FL01, receive path404-B includes amixer428 that mixes the outputs ofamplifiers424 and408 and anamplifier430. Also, the pulse widths of pulse signal TPULSE can be about 40 ps or 80 ps when the signal FL01 has a frequency of about 50 GHz.
• Turning toFIG. 10, yet another alternative one of transceivers202-1 to202-N (referred to as202-C) can be seen in greater detail. Here, D flip-flop432 has been included in the path for the pulse signal TPULSE; namely, the input terminal of flip-flop432 receives the pulse signal TPULSE, while flip-flop is clocked by the output ofamplifier408. Additionally,multiplier416 andamplifier418 have been replaced byamplifier434. This arrangement is generally useful for even lower frequency ranges (i.e., 40 GHz), which can produce pulse widths for pulse signal TPULSE are about 50 ps or 100 ps.
• InFIG. 11, another alternative one of transceivers202-1 to202-N (referred to as202-D) can be seen in greater detail. Here, the transmit path402-D is similar to path204-A; however, multiplier410-A has been replaced with multiplier410-D, whileamplifier408 has been removed. Multiplier410-D generally has a lower range to accommodate a signal FL01 with a high frequency. For example, if signal FL01 has a frequency of about 100 GHz, then multiplier410-D can be a multiply-by-2 multiplier. Additionally, for receive path404-D,multiplier416 andamplifier418 have been removed so thatmixer422 mixes the output ofLNA420 with the output ofphase shifter406.
• Turning now toFIG. 12, a circuit diagram of an example ofmultipliers410 and/or416 can be seen. This type ofmultiplier410 and/or416 is generally employed within transceivers202-1 to202-N to produce very high frequencies (i.e., 200 GHz) because direct production of these high frequency signals is very difficult. Generally,multiplier410 and/or416 employs a differential choke802, arectifying interleaver804, and aVCO806. Typically,VCO806 uses two oscillator tanks to generate two pairs of output signals from differential in-phase signals VIP and VIM and differential quadrature signals VQM and VQP. Typically,VCO806 comprises MOS transistors Q5 through Q12, inductors L3 through L6, and capacitors C1 and C2. Rectifyinginterleaver804 employs two differential pairs of transistors Q1/Q2 and Q3/Q4 andcurrent sources810 and812 to interleave the outputs fromVCO806 to generate a single-ended output signal OUT. Additionally, atermination808 and inductors L1 and L2 (from differential choke802) are coupled to therectifying interleaver804. Typically, power output is sufficient to lock ILCVO412 (i.e., −20 bBm).
• InFIG. 13, an example ofphase adjuster406 can be seen. Here, a differential input signal IN (which is generally signal FL01 from LO202) is provided to differential pairs of MOS transistors Q13/14, Q15/Q16, Q17/Q18, and Q19/Q20 (which are also coupled to inductors L7 and L8). Based on control signals VC1 through VC4 received from controller236, transistors Q21 through Q24 can activate the differential pairs Q13/14, Q15/Q16, Q17/Q18, and Q19/Q20 to generate a phase rotation of the differential input signal IN, having a total phase shift range of less than about ±22.5°. Typically, phase shifting is performed in the lower frequency domain (i.e., 50 GHz) to generally ease any bandwidth requirements and efficiently recover power losses.
• Turning toFIG. 14, a circuit diagram of an example ofILVCO412 can be seen.ILVCO412 is generally employed because of the losses frommultiplier410. Theoretically,ILVCO412 can provide an infinite gain if the center frequencies match with a finite gain throughout the locking range. Typically, MOS transistors Q25 and Q28 are coupled at their respective gates tobalun1002, which receives an output from multiplier410 (i.e.,410-A,410-B, or410-C). In an alternative configuration, MOS transistor Q28 can receive receives an output from multiplier410 (i.e.,410-A,410-B, or410-C) at its gate, while MOS transistor Q28 receives the pulse signal TPULSE at its gate. These transistors Q25 and Q28 are generally coupled in parallel to a gain stage (which is generally comprised of cross-coupled MOS transistors Q26 and Q27) and the oscillator tank (which is generally comprised of capacitors C3 and C4 and inductors L9 and L10). Alternatively, the second harmonic of the output can be used instead of first harmonic to relax any tuning range requirements, but with reduced output power. As an illustration, the properties ofILVCO412 can be seen in Table 1 below using both the first and second harmonics.

• 	TABLE 1
  	Targets	First Harmonic	Second Harmonic

  	Input Frequency [GHz]	200	100
  	Output Frequency [GHz]	200	200
  	Power Output [dBm]	−12	−12
  	Phase locking	@200 GHz	@100 GHz

• InFIG. 15, a circuit diagram for an example ofPA414 and/orLNA420 can be seen. Generally, thePA414 and/orLNA420 can provide linear amplification and isolation, and one of the features ofPA414 and/orLNA420 is its ability to be power gated with a fast pulse time (i.e., tens of picoseconds).PA414 and/orLNA420 generally comprise inductors L11 through L15, capacitors C5 through C7, and transistors Q29 and Q30. Here, the capacitors C5 through C7 are resonated by series or shunt inductors L11 through L15 to provide the amplification with transistors Q29 and Q30. Additionally, the input and output ofPA414 and/orLNA420 can be matched input or output impedances. For example, forPA414, the output impedance can be matched to theradiator426. Moreover, the circuit shown inFIG. 11 can be cascaded in multiple stages, where the gain can be between 0 and 2 dB per stage.
• Turning toFIG. 16, an example of aradiation426 can be seen. Here,radiator426 is shown as being a patch antenna formed over asubstrate210. This patch antenna generally comprises apatch1204 having slots128 that are generally parallel to ground strips and radiatingedges1202. For a frequency of about 410 GHz (which has a wavelength of about 0.75 mm in air), the width W and length L ofpatch1204 are each about 200 μm, while the slots are 2 μm wide. The proportions of the patch antenna can then be varied so as to accommodate a desired emission frequency (and wavelength). These radiators426 (i.e., patch antennas) can then be formed into an array as shown inFIG. 17. Alternatively,radiator426 can be a bondwire Yagi-Uda antenna.
• Because the data bandwidth ofsystem200 is very high (i.e., on the order of tens of gigahertz), it is generally impractical to employ an ADC that digitizes the signals receives through by thereceiver circuitry228. InFIGS. 18 and 19, timing diagrams can be seen that generally depict the operation of thereceiver circuitry228, where each uses a trigger signal to reconstruct the received signal. ForFIG. 18,variable selector220 actuates switches218-1 to218-N at various periods (i.e., Δ₁to Δ₄) following the trigger signal to allow each of the ADCs222-1 to222-N to resolves a portion of the received signal.FIG. 19, on the other hand, use an envelop signal following the periods (i.e., Δ₁to Δ₄) as part of the control mechanism for switches218-1 to218-N.
• To accomplish this, there are several approaches that can be taken. InFIG. 20, an example for one arrangement can be seen. In this arrangement, the switches218-1 to218-N are comprised of zener diodes D1 to DN, capacitors CS1 to CSN, and pulse circuits1602-1 to1602-N (which are generally controlled by the variable selector220). These switches218-1 to218-N operate as an input sampling network where each capacitor CS1 to CSN is coupled to a “slow” ADC222-1 to222-N. Generally, this approach may require very small apertures and very accurate clock generation.
• Another arrangement can be seen inFIG. 21. For this arrangement, ADCs222-1 to222-N (referred to as222) are low pass/band pass sigma-delta converters that can directly digitize about a 10 GHz bandwidth with a clock of about 100 GHz.ADC222 generally comprises afilter1702, aquantizer1704, adelay1712, a digital-to-analog converter (DAC)1714, andamplifiers1716 and1718. Thequantizer1704 generally comprises quantizers1706-1 and1706-2,clock divider1710, andmultiplexer1708. In operation, a feedback signal (which is amplified by amplifier1718) is combined with the input signal and filtered byfilter1702. This filtered output is combined with the feedback signal (which is amplified by amplifier1716). Quantizer1704 (which is generally an 2-bit, 2-way interleaved quantizer operating at 1.5 GHz) quantizes the signal (which is then delayed bydelay1712 and converted to a feedback signal by DAC1714).
• Thefilter1702 can be seen in greater detail inFIG. 22. In particular, thefilter1702 operates as amplifier and LC filter. To accomplish this,filter1702 generally comprises a trasconductor cell1804 (which generally comprises transistors Q31 through Q36,linearizer1802 and switches S1 and S2) and a negative transconductor cell1806 (which generally comprises transistors Q37 through Q40) that are each coupled to an LC circuit1808 (which generally comprises inductors L16 and L17 and capacitor C8).
• Yet another approach can be seen inFIGS. 23,24, and25. Here, a time todigital converter1902 is coupled to each ADC222-1 to222-N; only one ADC, labeled222, is shown, however. Thisconverter1902 has sub-picosecond resolution and, in operation, enabled when the input signal transitions to logic high or “1.” This activates thegated ring oscillator1904 so that thecounters1906 can performed counting operations from the taps of theoscillator1904. The outputs from thecounters1904 can then be summed and stored inregister1904.
• Turning toFIG. 26, a circuit diagram of an example of summingcircuit210 can be seen. Typically, summingcircuit210 is a summing amplifier that is formed as a summing amplifier tree. As shown inFIG. 20, each summing circuit or summingamplifier2002 receives a pair of input signals. At the first stage2004-1 of the tree each summingcircuit2002 is coupled to a pair of transceivers (i.e.,204-1 and204-1). Then each subsequence stage (i.e.,2004-2) receives input signals from a pair of summingcircuits2002 from the previous stage (i.e.,2004-1). As a result the tree has a depth of log₂N, where N is the number of transceivers204-1 to204-N.
• As stated above, for a monolithically integrated, low power IC that includessystem200, this range is generally less than one meter. Thus, it should be apparent that in the terahertz frequency range, there is a shortage of available power, which results in decreased sensitivity, and with other frequency range systems being available that have fewer limitations than terahertz systems, transmission and reception in the terahertz range usually becomes attractive when there is a large increase in available bandwidth. However, transmitting, receiving, and digitizing such large bandwidths (i.e., >10 GHz) can be problematic due at least in part on analog-to-digital converter (ADC) performance requirements.
• These issues, though, are addressed insystem200. In particular,system200 generally employs an increased pulse repetition frequency (PRF) of the terahertz radar so as to reduce coherency losses due to target motion. By making use of a high PRF, a small portion (subset) of the total available time for reception can be digitized, and by scanning this subset rapidly, it is possible to generate the full reception interval, reducing the overhead for a very high sampling frequency on the ADC. The high PRF can also generally ensure that it is possible to digitize the desired reception interval very quickly. Additionally, because of the lack of signal power, most signals should include baseband averaging of pulse reception, insystem200 some averaging is performed in the analog domain so as to reduce the ADC and digitization conversion rate to be equal to the PRF, which is an easily manageable task.
• Turning toFIGS. 27 and 28,alternative receiver circuitry228 can be seen. As shown, thiscircuitry228 includes an analog baseband circuit2116, which performs the analog averaging and digitization forsystem200. The analog baseband circuit2116 generally comprises an in-phase or I channel3001, a quadrature orQ channel3003, aclock circuit3005, and anoutput circuit3014. Each of thesechannels3001 and3003 generally and respectively includes a low noise amplifier (LNA)3002-1 and3002-2, an averager3004-1 and3004-2, an amplifier3006-1 and3006-2, and an ADC3008-1 and3008-2. Theclock circuit3005 generally comprises a clock generator3010 (which can generate an ADC clock signal ADCCLK[L] and a clear signal CLR[L]) and a DLL3012 (which can generate a sample clock signal SAMPLECLK[L]).
• In operation, a digital output signal RXDATA and clock signal ADCCLKOUT are generated from the baseband input signals BBI and BBQ and DLL clock signal RXDLL. Typically, BBI and BBQ are differential signal (as shown), but may also be single-ended. These I and Q baseband signals BBI and BBQ (which are generally received from the summing circuitry210) are respectively amplified by amplifiers3002-1 and3002-2. Because there are difficulties in digitizing the high bandwidth (as explained above), the performance requirements for ADCs3008-1 and3008-2 can be reduced by averaging the output of LNAs3002-1 and3002-1 with averagers3004-1 and3004-2.
• The averagers3008-1 and3008-2 (which can be seen in greater detail inFIGS. 29 and 30) generally comprise switched capacitor banks4002-1 to4002-R with each bank having several branches5002-1 to5002-J; for example and as shown inFIG. 30, each branch (which is labeled4002) has J branches. As with the baseband signals BBQ and BBI, branches5002-1 to5002-J are arranged to receive differential signals, but branches502-1 to502-J can be arranged to receive single-ended signals. These branches5002-1 to5002-J generally and respectively comprise sample switches S1-1 to S1-J and S5-1 to S5-J, capacitors C1-1 to C1-J and C2-1 to C2-J, clear switches S3-1 to S3-J and S4-1 to S4-J, and output switches S2-1 to S2-J and S6-1 to S6-J. The sample switches S1-1 to S1-J and S5-1 to S5-J are each generally coupled to a tap of theDLL3014 so as to receive branch sample signals SAMPLE1 to SAMPLEL, respectively (where sample clock signal SAMPLECLK[L] is generally comprised of clock signals SAMPLE1 to SAMPLL). Moreover, the clear signal CLR[L] (which generally comprises branch clear signals CLR1 to CLRL) can actuate switches S3-1 to S3-J and S4-1 to S4-J to discharge capacitors C1-1 to C1-J and C2-1 to C2-J, while the output switches S2-1 to S2-J and S6-1 to S6-J are actuated by the ADC clock signal ADCCLK[L] (which generally comprises branch readout signals ADCCLK1 to ADCCLKL).
• Turning toFIG. 31, an example of the operation of the analog baseband circuit2116 (and system200) can be seen. Typically, thecontroller230 adjusts the phase shift for each of the transceivers206-1 to206-N (for this example) to direct a beam of terahertz radiation emitted from the phasedarray204 so as to be aligned and optically coupled with thetouch panel102. This emitted radiation is in the form of a pulse that can be directed toward thetouch panel102 so that reflected radiation (i.e., from the object110) can be received by the transceivers206-1 to206-N. These transmitted pulses TXPulse can (for example) each a width of about 100 ps that would correspond to a distance of about 1.5 cm and can be separated from one another by at least an unambiguous range or duration6002 (which allows ample time for reset and detection) between times TO and TPRI (which is the pulse repetition interval). This unambiguous range6002 can, for example, be 9.9 ns or 1.485 m, which can correspond to a 100 MHz pulsing frequency. Within this unambiguous range6002, there is ascan range6004 between the minimum and maximum target distances andunused ranges6007 and6008. The minimum target distance is generally dictated by far field conditions and may be, for example, about 3 cm, while the maximum target distance is generally limited by the available power reflected by the target and sensitivity of the transceivers204-1 to204-N (which may be, for example, about 24 cm). Thescan range6004 can be divided into number of range cells (not shown inFIG. 31 for the sake of simplicity) that each have approximately the same width as the transmitted pulse TXPulse (i.e., 100 ps), and a set (i.e., 4) of the range cells can be arranged into adigitization window6006, having a total width of (for example) about 400 ps. Thedigitization window6006 allows for the reflected and received radiation to be digitized. Additionally, thesetup period6010 following thescan range6004 can be used as setup time for analog transmission.
• InFIG. 32, the structure and operation ofdigitization window6006 can be seen in greater detail. As described above, thedigitization window6006 is generally comprised of a set of range cells; in this example, there are four range cells7004-1 to7004-4 inwindow6006. Each of the range cells7004-1 to7004-4 can then be subdivided into sampling instants (i.e.,7006). Again, in this example, there are four sampling instants per range cell7004-1 to7004-4 (with a total of 16). Since each sampling instant (i.e.,7006) is generally associated with a branch (i.e.,5002-1), it can be assumed for this example that there are four transceivers (i.e.,206-1 to206-4), four switched capacitor banks (i.e.,4002-1 to4002-4) with four branches each (i.e.,5002-1 to5002-4), sixteen branch sample signals (i.e., SAMPLE1 to SAMPLE16), and sixteen dump branch signals (i.e., SAMPLE1 to SAMPLE16). Additionally, the sampling instants (i.e.,608) can, for example, be separated from one another by 25 ps.
• Duringdigitization window6006, averaging of the baseband signals BBI and BBQ is performed. The branch sample signals SAMPLE1 to SAMPLE16 (for the example ofFIG. 32) are asserted on each successive sampling instant (i.e.,6008) withindigitization window6006 so as to actuate sample switches S1-1 to S1-4 and S5-1 to S5-4 for each branch4002-1 to4002-4. These branch sample signals SAMPLE1 to SAMPLE16, in this example, are asserted for substantially the same duration as each of sub-range cell or sampling period (i.e., time between sampling instants which can be about 25 ps). This process is then repeated over a predetermined number (i.e., 16) of transmitted pulses TXPulse (generally in consecutive cycles) such that the each capacitor C1-1 to C1-4 for each branch4002-1 to4002-4 measures the same sub-range cell or same sampling period during each of the repeated cycles. This allows the capacitors C1-1 to C1-4 for each branch4002-1 to4002-4 to “average” its amplified baseband signal (i.e., BBI or BBQ) for its sub-range cell or sampling period over the predetermined number of cycles. Following the completion of the predetermined number of cycles, the ADC clock signal ADCCLK[L] (which is generally synchronized with the sample signal SAMPLECLK[L]) can be asserted so as to actuate output switches S2-1 to S2-4 and S6-1 to S6-4 for each branch4002-1 to4002-4 in order so that ADCs3008-1 and3008-2 can readout and digitize the averaged voltages from each of capacitors C1-1 to C1-4 for each branch4002-1 to4002-4. Once the ADCs3008-1 and3008-2 readout the averaged voltages from each of capacitors C1-1 to C1-4 for each branch4002-1 to4002-4, the branch clear signals CLR1 to CLR16 are asserted so as to actuate clear switches S3-1 to S3-46 and S4-1 to S4-4 for each branch4002-1 to4002-4 to discharge capacitors C1-1 to C1-4 and C2-1 to C2-4 for each branch4002-1 to4002-4.
• Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims (18)

1. A method comprising:

transmitting a pulse of terahertz radiation through a touch panel formed of a dielectric material such that the pulse generates a evanescent field in a region adjacent to a touch surface of the touch panel;

generating a reflected pulse from an object located within the region adjacent to the touch surface of the touch panel; and

triangulating a position of the object on the touch surface of the touch panel at least in part from the reflected pulse.

2. The method ofclaim 1, wherein the step of triangulating further comprises:

receiving the reflected pulse by a first receiver and a second receiver that are separated from one another by a distance; and

calculating the position of the object based at least in part on a first elapsed time between transmission and reception at the first receiver, a second elapsed time between transmission and reception at the second receiver, and the distance.

3. The method ofclaim 1, wherein the reflected pulse further comprises a first reflected pulse, and wherein the step of triangulating further comprises:

generating a second reflected pulse from a reflector included in the touch panel;

receiving the first and second reflected pulses by a receiver; and

calculating the position of the objected from the first and second reflected pulses.

4. The method ofclaim 3, wherein the reflector is located along the periphery of the touch panel.

5. The method ofclaim 1, wherein the pulse further comprises a first pulse, and wherein the reflected pulse further comprises a first reflected pulse, and wherein the first pulse is transmitted by a first transceiver, and wherein the method further comprises:

transmitting a second pulse of terahertz radiation through a touch panel by a second transceiver; and

generating a second reflected pulse from an object located within the region adjacent to the touch surface of the touch panel.

6. The method ofclaim 5, wherein the step of triangulating further comprises triangulating the location of the object on the touch surface of the touch panel from the first and second reflected pulses.

7. An apparatus comprising:

a touch panel formed of a dielectric material that is configured to carry terahertz radiation and having a touch surface; and

a touch controller that is optically coupled to touch panel, wherein the touch controller is configured to transmit a pulse of terahertz radiation through the touch panel so as to generate a evanescent field in a region adjacent to the touch surface, and wherein the touch controller is configured to receive a reflected pulse that is generated by an object located within the region, and wherein the touch controller is configured to triangulate a position of the object on the touch surface at least in part from the reflected pulse.

8. The apparatus ofclaim 7, wherein the touch controller further comprises:

a signaling circuit that is configured to generate and receive terahertz radiation; and

a control circuit that is coupled to the signal circuit.

9. The apparatus ofclaim 8, wherein the signaling circuit further comprises:

a transceiver;

a local oscillator that is coupled to the transceiver; and

a receiver circuitry that is coupled to the transceiver.

10. The apparatus ofclaim 9, wherein the receiver circuitry further comprises an analog baseband circuit that averages the combined signal for a plurality of sampling periods within a digitization window to generate a plurality of averaged signals and that converts the plurality of averaged signals to a digital signal.

11. The apparatus ofclaim 10, wherein the analog baseband circuit further comprises:

a clock circuit;

a low noise amplifier (LNA) that is coupled to the summing circuit;

an averager that is coupled to the LNA and the clock circuit;

an analog-to-digital converter (ADC) that is coupled to the LNA and the clock circuit; and

an output circuit that is coupled to the ADC.

12. The apparatus ofclaim 11, wherein the transmitter further comprises:

a transmitter that is coupled to the local oscillator; and

a plurality of receivers that are spaced apart from one another and that are each coupled to the receiver circuitry.

13. The apparatus ofclaim 12, wherein the touch panel further comprises a reflector.

14. A method comprising:

transmitting a pulse of terahertz radiation through a touch panel formed of a dielectric material such that the pulse generates a evanescent field in a region adjacent to a touch surface of the touch panel;

generating a plurality of reflected pulses, wherein a first reflected pulse is generated by a object located within the region adjacent to the touch surface of the touch panel; and

triangulating a position of the object on the touch surface of the touch panel at least in part from the plurality of reflected pulses.

15. The method ofclaim 14, wherein the object further comprises a first object, and wherein the position further comprises a first position, and wherein a second reflected pulse of the plurality of reflected pulses is generated by a object located within the region adjacent to the touch surface of the touch panel and at a second location.

16. The method ofclaim 15, wherein the step of triangulating further comprises:

receiving the plurality of reflected pulses by a first receiver and a second receiver that are separated from one another by a distance; and

calculating the position of the object based at least in part on the plurality of reflected pulses.

17. The method ofclaim 16, wherein a third reflected pulse of the plurality of reflected pulses is generated by a reflector.

18. The method ofclaim 17, wherein the reflector is located along the periphery of the touch panel.

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