SU1181147A1 - Voltage-to-frequency converter - Google Patents

Abstract

A FREQUENCY VOLTAGE CONVERTER containing a comparator, a single-vibration device, a resistor, a capacitor and an operational amplifier, the inverting input of which is connected to the device input through a resistor, one capacitor plate is connected to the inverting input of the operational amplifier and the other to the input of the comparator whose output is connected to the input of a single-vibration characterized in that, in order to increase the accuracy of the conversion, a reference voltage source, a second operational amplifier and a two-position switch are introduced into it, and the output of the reference voltage source is connected to the non-inverting input of the second operational amplifier, the inverting input of which 9 is connected to the inverting input of the first operational amplifier, the inputs of the two-position switch are connected to the outputs of the operational amplifiers, its output is connected to the input; do the comparator, and the control input key is connected to the output of the one-shot. Vtijf -H} - Hf 1 H

Description

I

The invention relates to an information-measuring technique and can be used in analog-digital converters.

The purpose of the invention is to improve the accuracy of conversion.

FIG. 1 is a functional diagram of the deviceJ in FIG. 2 is a time chart illustrating the operation of the device.

The voltage to frequency converter contains an operation amplifier 1, a resistor 2, a capacitor 3, a comparator 4, a one-shot 5, a source 6 of the reference voltage, onepauHoihibM amplifier 7, a two-position switch 8.

The inverting input of the operational amplifier 1 is connected via a resistor 2 to the device input, one capacitor plate 3 is connected to the inverting input of the operational amplifier 1, and the other to the input of a comparator 4, the output of which is connected to the input of a single vibrator 5, as well as a source of reference voltage 6, the second operating voltage the amplifier 7 and the on-off switch 8, the output of the source 6 of the reference voltage is connected to the non-inverting input of the second operational amplifier 7, the inverting input of which is connected to the inverting input of the primary The first operational amplifier 1, the inputs of the on-off key are connected to the outputs of the operational amplifiers, its output is connected to the input of the comparator 4, and the control input of the key is connected to the output of the one-oscillator 5.

The device works as follows.

in a way. I

At time t, the potential at

the plate of the capacitor 3, facing the comparator 4, is zero. The comparator is triggered (the comparison level is equal to zero) and through the one-shot 5 sets the switch 8 to the upper position. In this case, the capacitor 3 is included in the negative feedback circuit of amplifier 7. As a result, at time t, the potential at the inverting input of the amplifier (l jumps to a value equal to P, where UQ is the voltage at the output of the reference voltage source 6. There is a similar jump at the input comparator 4 (Fig. 2).

472

After this, the charge of the capacitor 3 with current begins.

Uo-Ux (il

i (t)

where R is the resistance of resistor 2. In the time from t to tg, the voltage across the capacitor is incremented by

. , S; -uxit) ,, ..

at time t, switch 8 switches to the lower position (capacitor 3 is included in the negative feedback circuit of amplifier 1). The potential of the inverting input of amplifier 1 changes abruptly from the value of Up to 0. Exactly at the same level, the voltage decreases abruptly.

at the input of the comparator (Fig. 2).

0x, to After this, the voltage at the input of the comparator 4 begins to decrease. At time t, it reaches zero level, the comparator 4 is triggered, and then the processes in the circuit are repeated.

Over time from t to t, the negative voltage increment on the capacitor will be

ii

II 11 I

(2)

It's obvious that

whether; + & Uc

0

Substituting equalities (1) and (2) into the last equation and solving it with respect to f 1 / T, we obtain (teach that tg - t, t,

t - to).

H

where U, is the average value of the input voltage Uj over time from t to tj, (t). The output frequency of the preloaded device does not depend on the resistance of resistor 2 (the conversion function according to formula (3)), the instability of which is the source of the corresponding error. Another advantage of the proposed converter is the use of 3

a reference voltage source instead of a reference current source, which eliminates the conversion of the reference voltage into a reference current.

In the proposed device, the error introduced by the imperfect key 8 (for example, the final R-5 values of the closed key and Rp of the open key, as well as residual currents and voltages) is almost completely eliminated due to the fact that in any key condition direct conversion circuit of a closed control loop. For the same reason, the effect of the resistance Rp is not affected. If key 8 is in the position shown in FIG. 1, then the presence of the resistance RP 7 co between the output of the operational amplifier 7 and the output of the switch 8 leads to an effect on the output of switch 8 of some additive equivalent voltage equal to

H7

, 1 o

R

1811474

where and „7“ is the voltage of the naxcemium amplifier 7 (caused by the action at its input of the voltage Uj,) J

5 Riow siB is equivalent (taking into account negative feedback through capacitor 3) the output resistance of the closed system, including) 0 amplifier 1 and resistance R- in the direct circuit and capacitor 3 in the feedback circuit. R because of the presence of a deep negative feedback, the effect at the output of the specified closed system leads i to a slight change in the statistical error, the value 2Q transmitted to the input of the amplifier 1, which is obviously equal to

I)

ay) s.ekb

eq RP-K,

k,

where K is the gain of the operational amplifier 1. Since RP Rgy and K, 1, the presence of such a small change in the static error can be neglected.

yy

Sx.K

Ifo

A

Vn

Claims (1)

A FREQUENCY VOLTAGE CONVERTER containing a comparator, one-shot, resistor, capacitor and an operational amplifier, the inverting input of which is connected through the resistor to the input of the device, one capacitor plate is connected to the inverting input of the operational amplifier, and the other is connected to the input of the comparator, the output of which is connected to the input of the single-shot , characterized in that, in order to increase the accuracy of the conversion, a reference voltage source, a second operational amplifier and a two-position switch are introduced into it, and the output The reference voltage source is connected to the non-inverting input of the second operational amplifier, the inverting input of which is connected to the inverting input of the first operational amplifier, the inputs of the on-off switch are connected to the outputs of the operational amplifiers * *, its output is connected to the comparator input, and the control input of the key is connected to the output of the one-shot. φυι. 1