GB857862A - Improvements relating to signal processing systems - Google Patents

Abstract

857,862. Multiplexing and analogue-to-digital converters. GENERAL ELECTRIC CO. May 31, 1957, No. 17412/57. Class 40 (1). To transmit, in serial pulse form, digital representations of a number of analogue values, the analogue values are sampled in turn, each sample being converted into a digital representation and, at the same time a channel identifying signal is generated there being serialising means for transmitting each channel signal followed by the corresponding digital value signal. In Fig. 1, the analogue values are voltages on leads which are arranged in groups A1- An, B1-Bn, &c., one of these groups being selected by a push-button and connected via leads 3 to the programmer 4, The programmer connects each lead in turn via lead 5 to an analogue-to-digital converter 6 and generates on leads 12 a signal identifying the lead connected. The output from the converter appears as a combination of markings on eight leads 7 which are applied to a relay unit 8. The outputs on leads 9 pass together with the lead identifying number on leads 12 to the serialiser 10 which produces the serial pulse signal representing lead number and the input value. An indication of the group "A," say, to which these signals relate is passed on leads 17 to the relay unit 8 and is transmitted in a preliminary group-indicating cycle before the sequential sampling of the leads 3. It is preceded by a signal from lines 12 in this preliminary cycle indicating that what follows identifies the group. Other information in the form of a discrete message is entered into the relay unit 8 on leads 18. Detailed circuit, Fig. 3.-The transmitter is controlled by a 6-cycle per second multivibrator 19, the output of which passes via lead 20 and amplifier 21 to operate a stepping switch 22, forming the selector of programmer 4. Leads 29, 30, 31 and 32 are energized by four banks of switch 22 to provide an indication of the lead number 1-n identifying the channel being sampled. These signals are serialised on lead 11 by scanner 10 controlled by a flip-flop counter 34 counting in a scale of 13. The counter is driven by pulses at the rate of 100 per second from generator 37, and gated to the counter under the control of flip-flop 35. Relay 28 gives an output at the trailing edge of the short pulse from the multivibrator, this output setting flip-flop 35 to allow pulses to pass to the counter. The four stages are connected to count 13 by an initial entry of three. This is derived from circuit 39 which when made operative by a differentiated pulse from the relay 28, presets the first two stages. Analogue-to-digital converter.-At the same time as the lead number on lines 29-32 is read out by scanner 10, the analogue voltage on the selected lead, now appearing on lead 5, is converted to a digital representation. For this purpose it is compared in comparator 49 with the output of a linear time-base voltage generator 48 and a pulse is generated to indicate that equality has been reached. The time-base is started by a flip-flop 45 which at the same time gates pulses from a 16,000 c.p.s. generator into an eight-stage binary counter 41. The flipflop is reset by the equality pulse, the count in the counter 41 then being representative of the analogue signal on line 5. By the time the scanner has read out the four leads 29-32, the counter 41 is set and the value is made available on the parallel output leads. The scanner continues its operation without interruption and follows the lead number with the serialised digital equivalent of the analogue input. The next pulse from multivibrator 19 then steps the switch 22, the next channel and the process is repeated. In the last position of switch 22, a multivibrator 52 is energized and delivers a pulse to operate relay 8 which has a number of contacts controlling the input to the scanning circuit 10 ready for the group-indicating preliminary cycle. Group selection.-The " A " group of leads is selected by pressing the A button. This causes contacts to close to mark leads 57-59 with a binary signal " 110." Also contacts 55 and contacts 54 of relay 8 energize relay 61 to connect the " A " group of leads to the switch 22. When relay 8 operates, the leads 57-59 are connected to the scanner 10. The preliminary position of switch 22 applies a signal " 0001 " to leads 29-32 to indicate that the digits following define the group. When the scanner operates the signal " 0001 " is read out first, then the " A " group designation " 110 " and then five digits forming the addition information. After this " group " message has been sent, the multivibrator 52 returns to normal and the relay 8 relapses to connect the analogueto-digital converter output to the scanner 10 and the leads of the selected group are sampled in turn. The process is repeated with the leads of the same group until another button is pressed to select another group. The serialised output on lead 11 therefore consists of: a signal " 0001 " indicating that a group designation, e.g. " 110 " is to follow, the group designation, the additional message (5 digits), the first lead number of that group (4 digits), its sampled analogue value in 8 digits, the second lead number, its sampled analogue value and so on. Synchronizing.-A synchronizing signal sent out on lead 76 comprises a long negative pulse starting when flip-flop 73 is set by the setting of the first stage of counter 34 and reset by the output from the last stage. Instead of using transmission lines, wireless may be used, the data being sent as a frequency modulation of a carrier and the synchronizing signal as an amplitude modulation of the same carrier. Receiver, Fig. 6.-The synchronizing signal controls a timing circuit 79 which causes the serial data on line 11 to enter the stages of a shift register 81 from which it is transferred in parallel to an intermediate relay store 84. It is then distributed under control of the lead number to final stores 89, one for each lead, and converted back to an analogue representation by selecting certain ones of a series of resistor, weighted according to the binary scale. The outputs are distributed under the control of the group indication to appropriate ones of a series of leads A1-Xn corresponding to the input leads of Fig. 3. The group indication sets up a corresponding one of a number of relays in the first cycle to transfer the outputs from the seven digital to analogue converters to the appropriate seven of, say, 28 leads A1-Xn.