RU2642133C1 - Two-channel analogue-to-digital converter - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: proposed two-channel analogue-to-digital converter contains a key, a single-channel analogue-to-digital converter, a multiplexer with two registers on its outputs, and a shaper of the switching pulses whose output is connected to the control input of the key and multiplexer. The inputs of this two-channel analogue-to-digital converter are the inputs of the key channels, its outputs are the outputs of the registers, the output of the single-channel analogue-to-digital converter is connected to the input of the multiplexer. A short pulse shaper and an additional key, switched between the output of the first key and the input of a single-channel analogue-to-digital converter, are inputted to said converter. The second input of additional key is shorted and control input of this additional key is connected to the output of switching short pulse shaper, the input of which is connected to the output of the switching pulse shaper.

EFFECT: invention solves the problem of reducing the error.

2 cl, 2 dwg

Description

The invention relates to measuring equipment and electronic equipment and can be used to convert several analog signals to digital, which are used in various industries and in scientific research.

Precise conversion of analog signals to digital is required in all branches of technology: for measurement, for automatic or automated control, and for automated data collection and monitoring systems. These tasks are solved using analog-to-digital converters (ADCs). The input signals of such ADCs are analog electrical signals in the form of voltages that change relatively slowly over time. The output signals of the ADC are digital binary codes corresponding to the measurement results of the input signals. These codes are generated in the form of a sequence of pulses with levels of zeros and ones (sequential codes) or in the form of a parallel series of levels corresponding to zeros or ones issued to the corresponding buses. Since ADCs are often a relatively complex device, if you need to convert several slowly varying signals at the same time, they often use a switched ADC circuit. In this case, various signals are connected to the ADC input alternately with the keys, the ADC converts them, the received codes are interpreted as the result of converting the signal that was connected to the ADC input to receive these codes. In this case, the effective performance of the ADC is divided by the number of channels connected to it. The principle of the ADC can be considered on the example of a two-channel ADC, this principle can easily be extended to a larger number of channels.

A two-channel analog-to-digital converter is known, which contains a series-connected key, a sample-storage device, a single-channel ADC, a multiplexer, two registers at its outputs and a switching pulse shaper, one output of which is connected to the control inputs of the key and the multiplexer, the other output of which is connected to the control input sampling-storage devices, while the inputs of this two-channel analog-to-digital converter are the inputs of the key channels, its outputs are the outputs of the registers [V.A. Squeeze. On the use of ADC with sigma-delta modulation in switching mode. Automation and software engineering. 2016. No3 (17). S. 16-24. from. 17. Fig. 2, http://jurnal.nips.ru/sites/default/files/%D0%90%D0%90%D0%98%D0%9F%D0%98-3-2016-2.pdf].

This two-channel analog-to-digital Converter operates as follows.

The switching pulse generator generates pulses that control the key and the multiplexer. As a rule, the same time is allocated for converting each signal. For example, the output signal of the driver closes the first channel in the key and in the multiplexer at a low level of its output signal and closes the second channel in the key and multiplexer at a high level of this output signal. For example, in the initial state, the output signal of the shaper is low. The signal from the first key input enters through the key to the sampling-storage device (UVX), then to the single-channel ADC and is converted into a digital code. This digital code through the multiplexer enters the first register. At the end of the time allotted for the conversion, the output signal of the driver becomes a high-level signal, the key and the multiplexer close their second channels. Therefore, the signal from the second input of the key is received at the ADC through the key and the I / O, and the conversion result is transmitted to the second register through the multiplexer. For successful operation of the CVC, pulses are also needed that control its modes, which are also formed by the pulse shaper.

The disadvantage of such a multi-channel analog-to-digital converter is the large error. Each time, after switching the key, the sampling-storage device in this device starts a new transition process from its current state equal to the last value of the previous signal to the required state equal to the initial value of the subsequent signal. This gives rise to a large dynamic error, the value of which depends on the difference between the successively measured quantities. A large dynamic error also generates a static error and crosstalk, that is, the influence of the signal of each channel on the measurement result of signals in other channels.

Known for another two-channel analog-to-digital converter, adopted for the prototype, containing a key, a single-channel ADC, a multiplexer with two registers at its outputs, as well as a switching pulse shaper, the output of which is connected to the control inputs of the keys and the multiplexer, while the inputs of this two-channel analog-to-digital the converter is the key channel inputs, its outputs are the register outputs, the output of a single-channel ADC is connected to the input of the multiplexer [V.A. Squeeze. On the use of ADC with sigma-delta modulation in switching mode. Automation and software engineering. 2016. No3 (17). S. 16-24. from. 19. Fig. 4, http://jurnal.nips.ru/sites/default/files/%D0%90%D0%98%D0%9F%D0%98-3-2016-2.pdf].

This two-channel analog-to-digital Converter operates as follows.

As a single-channel ADC, an ADC is used that responds to the average value during its conversion, for example, an ADC with sigma-delta modulation. The principle of operation of such ADCs does not exclude the fact that the converted signal changes during its conversion, since the average value of the signal during its conversion is converted as a result. Such ADCs do not require high-frequency filtering of the input signal and do not require the use of I / O at their input. Otherwise, the operation of this multi-channel ADC is similar to the operation of the multi-channel ADC described above. The pulse from the output of the shaper sequentially takes on the value of high and low. With one value of this signal, the key and the multiplexer open their first channels. Therefore, a single-channel ADC is connected to the first input of the key, converts the signal at this input, and the result through the multiplexer enters the first register. With a different value of the control signal, the key and the multiplexer open their second channels, so a single-channel ADC is connected to the second input of the key, converts the signal at this input, and the result through the multiplexer enters the second register. Next, the cycle repeats.

The disadvantage of such a two-channel analog-to-digital converter is the large error. The single-channel ADC in this device each time after switching the key starts a new transient from its current state equal to the last value of the previous signal to the desired state equal to the initial value of the subsequent signal. This gives rise to a large dynamic error, the value of which depends on the difference between the successively measured quantities. A large dynamic error also generates a static error and crosstalk, that is, the influence of the signal of each channel on the measurement result of signals in other channels.

The objective (technical result) of the present invention is to reduce the error.

The problem is solved by the fact that a short-pulse shaper and an additional switch are inserted between the output of the first key and the input of the single-channel ADC in a two-channel analog-to-digital converter, while the second input of the additional key is shorted and the control input of this additional key is connected to the output of the switching pulse shaper , the input of which is connected to the output of the shaper pulses.

The proposed multi-channel ADC is shown in FIG. one.

A possible short pulse driver circuit is shown in FIG. 2.

The proposed multi-channel ADC (Fig. 1) contains:

1 key,

2 - single-channel ADC,

3 - multiplexer,

4, 5 - registers,

6 - shaper pulse switching

7 - an additional key,

8 - shaper of short pulses.

In this case, the second input of the additional key is shorted, and the control input of this key is connected to the output of the switching pulse shaper, the input of which is connected to the output of the short pulse shaper.

The short pulse shaper circuit, for example, may contain (Fig. 2):

9 is an exclusive OR diagram

10 - resistor

11 - capacitor.

In this case, the first input of the Exclusive OR circuit is the input of this shaper, the output of this circuit is the output of this shaper, the resistor leads are connected separately to the first and second inputs of this circuit, the capacitor leads are connected separately to the zero bus and the second input of this circuit .

In this case, a single-channel ADC is performed, for example, as an ADC with sigma-delta modulation, for example, the AD7714 microcircuit [http://www.analog.com/media/en/technical-documentation/data-sheets/AD7714.pdf].

Both keys and the multiplexer can be performed on chips, for example, the firm Analog Devices [http: // www. analog.com/en/products/switches-multiplexers/analog-switches-multiplexers.html].

Registers can be executed on the appropriate microcircuits, domestic (any series, for example, 555) or foreign [see, for example: Nefedov A.V., Savchenko A.M., Feoktistov Yu.F. / Ed. Shirokova Yu.F. Section 3. Digital integrated circuits and their electrical parameters // Foreign integrated circuits for industrial electronic equipment: Reference. - M .: Energoatomizdat, 1989 .-- 288 p. - ISBN 5-283-01540-8].

The switching pulse generator can be performed on microcircuits (generator, multivibrator), for example, on the K555GG1 microcircuit.

The short pulse shaper can be performed on microcircuits (multivibrator in standby mode), or on a timer, for example, K1006VI1.

The resistor can be, for example, type MLT-0.25-100 Ohm, the capacitor can be, for example, KM-5-1 nF.

The proposed two-channel analog-to-digital Converter operates as follows.

As a single-channel ADC 2, an ADC is used that responds to the average value during its conversion, for example, an ADC with sigma-delta modulation. The output signal of the pulse shaper switching 6 sequentially takes the values of high and low levels. This signal is fed to the control inputs of the key 1 and multiplexer 3 and controls the inclusion of the first or second channels. With one value of this signal, for example low, switch 1 and multiplexer 3 open their first channels. Therefore, the ADC 2 is connected with the key 1 to its first input, converts the signal on it, and the result through the multiplexer 3 goes to the first register 4. With a different value of the control signal, for example, high, the key 1 and multiplexer 3 open their second channels, therefore ADC 2 is connected via key 1 to its second input and converts the signal on it, and the result is transmitted via multiplexer 3 to second register 5. Next, the cycle repeats. In this case, each time a signal is changed at the output of the switching pulse shaper 6, the short pulse shaper 8 generates a short pulse that is supplied to the control input of the additional key 7. Under the control of this pulse, the key locks its first channel and opens the second channel, the input of which is shorted, i.e. it is connected to the device zero bus. Therefore, each time the input of the single-channel ADC 2 receives first a zero level from the shorted input of the additional key 7, and only then, after a short period of time corresponding to the pulse duration from the shaper of short pulses 8, the signal from the output of the key 1 comes to the input of this single-channel ADC, which should be converted. Therefore, every time at the beginning of the operation cycle, the input of the single-channel ADC 2 is shorted, and then connected to the corresponding input of the multi-channel ADC. Therefore, the operating conditions for each channel are identical and do not depend on the value of the signal level measured in the previous cycle. For this reason, the initial bias and crosstalk of the channels is eliminated, and, as a result, the error is reduced.

Thus, the present invention solves the problem of reducing the error.

Claims (2)

1. A two-channel analog-to-digital converter containing a key, a single-channel analog-to-digital converter, a multiplexer with two registers at its outputs, and a switching pulse generator, the output of which is connected to the control input of the key and the multiplexer, while the inputs of this two-channel analog-to-digital converter are the key channel inputs, its outputs are register outputs, the output of a single-channel analog-to-digital converter is connected to the input of the multiplexer, characterized in that in On the other hand, a short pulse shaper and an additional key are inserted between the output of the first key and the input of a single-channel analog-to-digital converter, while the second input of the additional key is shorted, and the control input of this additional key is connected to the output of the short pulse shaper, the input of which is connected to the output of the pulse shaper commutation. 2. The two-channel analog-to-digital converter according to claim 1, wherein the short-pulse shaper circuit contains an exclusive-OR circuit, a resistor, and a capacitor, the first input of the exclusive-OR circuit is the input of this former, the output of this circuit is the output of this former, the resistor leads are connected separately to the first and second inputs of this circuit, the capacitor leads are connected separately to the zero bus and the second input of this circuit.

Images