CN210091007U - Exponential function signal generating circuit - Google Patents

Abstract

The utility model provides an exponential function signal generating circuit, include: the device comprises a triangular wave adjusting circuit, a conversion circuit and a DAC chip for generating a triangular wave signal; the triangular wave adjusting circuit is used for adjusting the triangular wave signals generated by the DAC chip to be symmetrical about the X axis and outputting the triangular wave signals to the conversion circuit; and the conversion circuit is used for converting the triangular wave adjusted by the triangular wave adjusting circuit into an exponential function waveform and outputting the exponential function waveform. The low-cost DAC chip is used for generating the triangular wave, the general operational amplifier is used, the triode input/output characteristic curve is used for forming the amplifying circuit, the triangular wave is finally converted into an exponential function waveform to be output, the precision is high, the speed is high, and the technical barrier which cannot be achieved by direct digital synthesis is solved; the cost is low, and the problems of high cost and poor universality caused by using a special logarithmic operational amplifier are solved.

Description

Exponential function signal generating circuit

Technical Field

The utility model belongs to the technical field of signal generator, especially, relate to an exponential function signal generation circuit.

Background

Exponential and logarithmic function waveforms are widely used in the fields of acoustics and physics, where exponential functions, i.e., exponential anti-logarithmic functions, and logarithmic functions are inversely related to each other. There are two main methods for generating exponential or logarithmic curves: 1) the direct digital synthesis is generated through a direct digital frequency synthesizer; 2) converted by a special logarithmic operation amplifier chip.

Because the front end of the exponential curve changes slowly and the back end changes rapidly, the performance of the DAC chip dynamic and speed can not meet the requirements, the resolution of the DAC of the first half section of the direct digital synthesis exponential waveform is insufficient, and the conversion speed of the DAC of the second half section cannot follow. The Sigma-Delt type DAC has high precision but low speed, and the R-2R type DAC has high speed but low precision, so that a proper DAC cannot be found to realize direct digital synthesis exponential function waveform.

The special logarithmic operational amplifier is high in price, belongs to an extremely cold product, is high in price, is difficult to purchase, is not high in universality, and is fixed in shape of a function waveform and not adjustable in parameter.

Disclosure of Invention

In order to solve the above technical problem, the utility model provides an exponential function signal generating circuit. The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosed embodiments. This summary is not an extensive overview and is intended to neither identify key/critical elements nor delineate the scope of such embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

The utility model adopts the following technical scheme:

in some alternative embodiments, there is provided an exponential function signal generating circuit comprising: the device comprises a triangular wave adjusting circuit, a conversion circuit and a DAC chip for generating a triangular wave signal;

the triangular wave adjusting circuit is configured to adjust a triangular wave signal generated by the DAC chip to be symmetrical about an X axis and output the triangular wave signal to the conversion circuit, and the triangular wave adjusting circuit includes: the operational amplifier U2 is characterized in that a triangular wave signal output by the DAC chip VOUT pin is input from the non-inverting input end of the operational amplifier U2, and a reference voltage output by the DAC chip VREF pin is input from the inverting input end of the operational amplifier U2;

the conversion circuit is configured to convert the triangular wave adjusted by the triangular wave adjusting circuit into an exponential function waveform and output the exponential function waveform, and includes: the operational amplifier U3, a triode Q1, an operational amplifier U4 and a triode Q2, wherein the base of the triode Q1 is connected with the output end of the operational amplifier U2, the collector of the triode Q1 is connected with the inverting input end of the operational amplifier U3, the base of the triode Q2 is connected with the output end of the operational amplifier U4, the collector of the triode Q2 is connected with the inverting input end of the operational amplifier U4 and is connected with the output end of the operational amplifier U4 through a resistor R7, and the output end of the operational amplifier U3 is connected with the emitters of the triode Q1 and the triode Q2.

In some optional embodiments, the triangle wave adjusting circuit further comprises: resistance R1, resistance R2, resistance R3 and resistance R4, the VOUT pin of DAC chip is connected with operational amplifier U2's noninverting input end through resistance R1, and operational amplifier U2's noninverting input end is through resistance R2 ground connection, the VREF pin of DAC chip is connected with operational amplifier U2's inverting input end through resistance R3, and resistance R4 one end is connected with operational amplifier U2's inverting input end, and the other end is connected with operational amplifier U2's output.

In some optional embodiments, the triangle wave adjusting circuit further comprises: resistance R5 and resistance R6, the triangle wave adjusting circuit passes through resistance R5 and resistance R6 partial pressure, attenuates the certain multiple of amplitude attenuation of triangle wave, resistance R5 one end is connected with operational amplifier U2's output, and the other end is connected with triode Q1's base, and resistance R6 one end is connected with triode Q1's base, and the other end ground connection.

The utility model discloses the beneficial effect who brings: the low-cost DAC chip is used for generating the triangular wave, the general operational amplifier is used, the triode input/output characteristic curve is used for forming the amplifying circuit, the triangular wave is finally converted into an exponential function waveform to be output, the precision is high, the speed is high, and the technical barrier which cannot be achieved by direct digital synthesis is solved; the cost is low, and the problems of high cost and poor universality caused by using a special logarithmic operational amplifier are solved.

Drawings

Fig. 1 is a schematic circuit diagram of an exponential function signal generating circuit according to the present invention;

fig. 2 is a waveform diagram of the triangular wave converted into the exponential waveform by the exponential function signal generating circuit of the present invention.

Detailed Description

The following description and the drawings sufficiently illustrate specific embodiments of the invention to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. The examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others.

As shown in fig. 1-2, in some illustrative embodiments, there is provided an exponential function signal generating circuit comprising: a triangularwave adjusting circuit 1, aconversion circuit 2 and a DAC chip U1.

And the DAC chip 3 is used for generating a triangular wave signal. Since the slope of the triangular wave is fixed, the performance requirement of the DAC used for generating the triangular wave is low, and the chip model is DAC 8551. The digital signals 0-65535-0 are sequentially input, namely, the signals with gradually increased digital quantity and gradually decreased digital quantity are input to the SPI bus input end of the DAC chip, and a triangular wave which gradually rises and then gradually falls and has a fixed slope is generated at the output end of the DAC chip.

The digital input of the 16-bit DAC chip U1 corresponds to the output voltage VOUT, which is as follows:

VOUT＝VREF×DAC Code/65536；

VREF is a reference voltage of 4.1V, and the DAC Code value range is 0-65535. For example, a digital value is input to be 0, and the corresponding output voltage is 0V; the digital input is 65535 and the corresponding output voltage is 4.1V. The digital signals 0-65535-0 are sequentially and continuously input, the digital quantity gradually becomes larger and then gradually becomes smaller, the pin VOUT can generate triangular waves, the valley value of the triangular waves is 0V, the peak value of the triangular waves is 4.1V, and the triangular waves are located above an X axis.

And the triangular wave adjusting circuit is used for adjusting the triangular wave signal generated by the DAC chip U1 to be symmetrical about the X axis and outputting the triangular wave signal to the conversion circuit, and the triangular wave signal is in a triangular wave form required by amplitude and filling level exponent operation.

The triangular wave adjusting circuit includes: operational amplifier U2, resistance R1, resistance R2, resistance R3, resistance R4, resistance R5 and resistance R6. The VOUT pin of the DAC chip U1 is connected with the non-inverting input end of the operational amplifier U2 through a resistor R1, the non-inverting input end of the operational amplifier U2 is grounded through a resistor R2, the VREF pin of the DAC chip U1 is connected with the inverting input end of the operational amplifier U2 through a resistor R3, one end of the resistor R4 is connected with the inverting input end of the operational amplifier U2, and the other end of the resistor R2 is connected with the output end of the operational amplifier U2. One end of the resistor R5 is connected with the output end of the operational amplifier U2, the other end of the resistor R5 is connected with the base electrode of the triode Q1, one end of the resistor R6 is connected with the base electrode of the triode Q1, and the other end of the resistor R6 is grounded.

The triangular wave adjusting circuit shifts the triangular wave downward by 2.05V. The operational amplifier U2 is used to form a subtractor circuit, a triangular wave signal output from the VOUT pin of the DAC chip U1 is input from the non-inverting input terminal of the operational amplifier U2, and a reference voltage output from the VREF pin of the DAC chip U1 is input from the inverting input terminal of the operational amplifier U2.

The operational amplifier U2 output voltage equals:

VOUT×R1/(R1+R2)×(1+R4/R3)-Vref×(R4/R3)；

the triangular wave adjusting circuit divides the voltage through a resistor R5 and a resistor R6 to attenuate the amplitude of the triangular wave by a certain multiple.

And the conversion circuit is used for converting the triangular wave adjusted by the triangular wave adjusting circuit into an exponential function waveform and outputting the exponential function waveform. The conversion circuit includes: the operational amplifier U3, a triode Q1, an operational amplifier U4 and a triode Q2, wherein the base of the triode Q1 is connected with the output end of the operational amplifier U2, the collector of the triode Q1 is connected with the inverting input end of the operational amplifier U3, the base of the triode Q2 is connected with the output end of the operational amplifier U4, the collector of the triode Q2 is connected with the inverting input end of the operational amplifier U4 and is connected with the output end of the operational amplifier U4 through a resistor R7, and the output end of the operational amplifier U3 is connected with the emitters of the triode Q1 and the triode Q2.

The conversion circuit is an operational amplification circuit consisting of an operational amplifier U3 and a triode Q1, and the voltage at the point e is about 0.5V lower than that at thepoint b 1. The operational amplifier circuit composed of the operational amplifier U4 and the triode Q2 utilizes the inherent input characteristic curve of the triode Q2 to lead the current of the current i3 flowing through the resistor R7 to be changed exponentially under the control of the triangular wave voltage between b2 and e. Thus, the output voltage of the operational amplifier U4 is equal to: i3 xr 7, also varying exponentially.

The above embodiment is the preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above embodiment, and any other changes, modifications, replacements, combinations, simplifications, equivalent replacement modes, which are not departed from the spirit and principle of the present invention, should be included in the protection scope of the present invention.

Claims (3)

1. An exponential-function signal generating circuit, comprising: the device comprises a triangular wave adjusting circuit, a conversion circuit and a DAC chip for generating a triangular wave signal;

the triangular wave adjusting circuit is configured to adjust a triangular wave signal generated by the DAC chip to be symmetrical about an X axis and output the triangular wave signal to the conversion circuit, and the triangular wave adjusting circuit includes: the operational amplifier U2 is characterized in that a triangular wave signal output by the DAC chip VOUT pin is input from the non-inverting input end of the operational amplifier U2, and a reference voltage output by the DAC chip VREF pin is input from the inverting input end of the operational amplifier U2;

the conversion circuit is configured to convert the triangular wave adjusted by the triangular wave adjusting circuit into an exponential function waveform and output the exponential function waveform, and includes: the operational amplifier U3, a triode Q1, an operational amplifier U4 and a triode Q2, wherein the base of the triode Q1 is connected with the output end of the operational amplifier U2, the collector of the triode Q1 is connected with the inverting input end of the operational amplifier U3, the base of the triode Q2 is connected with the output end of the operational amplifier U4, the collector of the triode Q2 is connected with the inverting input end of the operational amplifier U4 and is connected with the output end of the operational amplifier U4 through a resistor R7, and the output end of the operational amplifier U3 is connected with the emitters of the triode Q1 and the triode Q2.

2. The exponential-function signal generating circuit of claim 1, wherein the triangular wave adjustment circuit further comprises: resistance R1, resistance R2, resistance R3 and resistance R4, the VOUT pin of DAC chip is connected with operational amplifier U2's noninverting input end through resistance R1, and operational amplifier U2's noninverting input end is through resistance R2 ground connection, the VREF pin of DAC chip is connected with operational amplifier U2's inverting input end through resistance R3, and resistance R4 one end is connected with operational amplifier U2's inverting input end, and the other end is connected with operational amplifier U2's output.

3. The exponential-function signal generating circuit of claim 2, wherein the triangular wave adjustment circuit further comprises: resistance R5 and resistance R6, the triangle wave adjusting circuit passes through resistance R5 and resistance R6 partial pressure, attenuates the certain multiple of amplitude attenuation of triangle wave, resistance R5 one end is connected with operational amplifier U2's output, and the other end is connected with triode Q1's base, and resistance R6 one end is connected with triode Q1's base, and the other end ground connection.

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