SU754441A1 - Logarithmic analogue -digital converter - Google Patents

Description

The invention relates to electrical signal converters with a logarithmic characteristic and can be used in computers.

One of the well-known logarithmic converters contains an exponential voltage generator, a comparator, a square wave generator Γι].

and Ι *

This device is characterized by low speed.

Of the known devices, the logarithmic analog-to-digital converter is the closest to the proposed one ₍ the comparator contains a comparison unit whose output is connected to the first input of the And element, to the second input of which the output of the clock generator is connected, the output of the And element is connected to _{2 (} summing input of the output the counter, the first input of the comparison unit is the input of a logarithmic analog-digital converter, the second input of the unit

2

comparison is connected to the output of the exponential voltage generator [2}.

A disadvantage of this device is the low speed, due to the principle of operation, according to which the conversion time of the input signal is determined by the time of generation of the exponential voltage and. recovery time of the original state.

The aim of the invention is to increase the speed of the device.

This goal is achieved by introducing the first and second key elements, the inverter and the additional element I, and the output of the exponential voltage generator through the first key element. the element is connected to the input of the inverter, and through the second key element to the input of the inverter, the output of the inverter is connected to the input of the exponential voltage generator, the first output of the comparison unit is connected to the control input of the first key element, the second output of the comparison unit is connected to

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the control input of the second key element and the first input of the additional element And, the first input of which is connected to the output of the clock, the output of the additional element And is connected to the subtractive input of the output counter.

Functional diagram of the proposed logarithmic analog-to-digital Converter shown in the drawing.

The converter contains a comparison unit 1, element 2. And, a clock pulse generator 3, an additional element 4 I, output counter 5, exponential voltage generator 6, first and second key elements 7 and 8, inverter 9, input 10 of a logarithmic analog-to-digital converter.

The operation of the device is based on a logarithmic transformation of the input signal increments at time intervals, followed by summation or subtraction (depending on the sign of the input signal increment) of the number of pulses during these intervals.

At a certain value of signal L at output 10, comparison block 1 is activated, the first key element 7 closes and element 2 I turns on. The time for which the specified elements are turned on is determined by the time constant of the exponential voltage generator 6, its output voltage and the value of the signal at input 10. This time is

1) B) H

and, ’(1)

15

20

where C is the time constant of the exponential voltage generator;

- the value of the input signal

YU;

- the output voltage of the generator 6 of the exponential voltage corresponding to the value of the signal at the input 10.

The code of the output counter 5 through time ,, determined from equality (1) will be equal to

N - - Yo T A T U

(2)

where t

- the repetition period of the signals from the generator output 3 clock pulses.

After the output voltage of the generator is 6 exponential

will become equal to the input one, the first key element 7 and the element 2 both turn off and the code of the output counter 5 remains equal to the relation (2).

If the signal at input 10 has changed / and adopted a new, larger value, then with the aid of the power of the comparison unit 1, the first key element 7 and element 2 I are included. The time during which these elements are turned on is

(h)

25

thirty

35

40

45

50

Where

- the magnitude of the signal at the input Yu;

0 ^ 2 - the output voltage of the generator 6 of the exponential voltage corresponding to the new value of the signal at output 10.

The number of pulses, which for the time determined from equality (3) will pass to the output counter · ’5, is proportional to this time. The code of the output counter 5 is equal to the sum of the codes before the change of the signal at input 10 and recorded over time (3) and is proportional to the logarithm of the input signal.

If the signal at input 10 has decreased, then using the comparison unit 1, the second key element 8 and the additional element I. are included.

The time during which these elements are open is determined similarly to expression (3) ..

The code of the output counter 5 will decrease by an amount proportional to the number of pulses transmitted to its subtracting input aa this time.

Thus, from the above ratios it can be seen that the code of the output counter 5 tracks changes in the input signal, and is proportional to the logarithm from it. Time - pulse conversion is carried out for the increments of the input signal, in contrast to the well-known conversion of the value of the input signal itself. Since the increments are smaller than the input signal, the conversion time to the code in the proposed device is less. In addition, the presence of a tracking mode for the input signal eliminates the need to set the initial state after each transformation. It also improves the speed of the device.

five

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6

Claims (1)

Claim A log-analog-to-digital converter containing a comparison unit, the output of which is connected to the first input of the element I, to the second input of which the output of the clock generator is connected, the output of the element AND is connected to the summing input of the output counter, the first input of the comparison unit is the input of the logarithmic analog-digital converter , the second input of the comparator is connected to the output of the exponential voltage generator, which differs in that, in order to improve performance, the first and Torah key elements, the inverter and the additional AND gate, the voltage exponential generator output through the first key element connected to the input of the inverter, and by a second key element - with inverter output, output. the inverter is connected to the generator input of the exponential voltage, the first output of the comparison unit is connected to the control input of the first key element, the second output of the comparison unit is connected to the control input of the second key element and the first input of the additional element I, the first input of which is connected to the output of the clock generator, output additionally The first element of the AND is connected to the subtracting input of the output counter.