SU1647428A1 - Linear ac root-mean-square voltage converter - Google Patents

Abstract

The invention relates to electrical measuring technology and can be used in the construction of analog and digital voltmeters of alternating voltage. The purpose of the invention is to improve the accuracy of conversion with small DC input signals. The device contains an unbalance amplifier 1, field-effect transistors 2 and 3, a low-pass filter 7, inverting amplifiers 9, 10 and 12. Introducing the full-wave rectifier 14, the switching element 15 and the pulse generator 18 ensures the elimination of additive errors due to the constant component voltage and bias voltages and input currents of the active elements of the circuit, while the additive errors of the inserted blocks do not affect the accuracy of the device. 1 il. (Ls

Description

The invention relates to electrical measuring technology and can be used in the construction of analog and digital voltmeters of alternating voltage.

The purpose of the invention is to improve the accuracy of conversion with small DC input signals.

The drawing shows a schematic diagram of the proposed Converter.

The linear converter contains unbalance amplifier 1, the first 2 and second 3 field-effect transistors, the gates of which are connected to each other, and the drain of the transistor 3 is connected to the input terminal 4 of the device, the first 5 and second 6 resistors,

The first terminals of which are connected and connected to the source of transistor 2, the second terminal of resistor 5 is connected to the drain of transistor 3, the low-pass filter 7, the output of which is connected to the output terminal 8 of the device, the drain of transistor 2 and through the first inverting amplifier 9 6, the second inverting amplifier 10 and the third resistor 11 connected in parallel between the source of the transistor 3 and the input of the filter 7, the third inverting amplifier 12, the input of which is connected to the drain of the transistor 3, and the output through the fourth resistor 13-k and 3. The transistor current converter also comprises a full-wave rectifier 14,

about

N

-h |

n3

with

switching element 15. Fifth 16 and sixth 17 resistors; 18 pulse generator. The information input, the control input, the first and second outputs of the switching element 15 are connected respectively to the source of the transistor 2, the output of the generator 18, the inverting and non-inverting inputs of the amplifier 1. The first terminals of the resistors 16 and 17 are connected to the common bus 19 of the device, and the second terminals - to the inverting and the non-inverting inputs of amplifier 1, respectively. The rectifier 14 is connected between the output of the amplifier 1 and the combined gates of transistors 2 and 3.

Linear Converter works as follows.

The cycle of the device consists of two cycles, equal to each other in duration. In one of the cycles, the switching element 15 connects to the inverting input of the unbalance amplifier 1 the source of transistor 2 and the first terminals of resistors 5 and 6. Then the inverting input of the amplifier 1 receives the input voltage UBx (t). On that. amplifier 1 through a resistor 6 is supplied with a constant voltage 11Vyh from the output of the filter 7 low frequencies. The output voltage of the amplifier 1 through the rectifier 14 causes the conduction channel of transistor 2 to change. The conductivity of the channel of the transistor 3 changes simultaneously. In this converter operation cycle, the rectifier 14 is a simple repeater of the output voltage of the unbalance amplifier 1. The relationship between the magnitudes of the conduction channel modulation of the transistor 2 and the values of the incoming input UBx (t) and voltage of the low-pass filter 7 can be determined from the equation

 UBX (t} - UCM} Gs + (Uab, x-UcM) -G2 - (iv.x + + iSm) -Sb O,

where UCM is the bias voltage at the invertibility of the input of amplifier 1, due to the temperature and time drift of the zero level;

Gs and Sat - conductivities of resistors 5 and 6;

Ga - conduction channel of the transistor 2.

From where

go - wih + ucm. UBX (t) -UCM. G

G2nGG- G6 -i i-trn 5

Willow UCMUBUX UCM

The output voltage of the amplifier is 10 U11o -U8Wx (t) (G3-Gi3) / Gii, where G3, Gn, Gi3 are the conductances of the transistor 3 channel and resistors 11 and 13. If the conductivities of the channels of transistors 2 and 3 placed on the same chip are the same, and the conductivities of resistors 6 and 13 are equal in magnitude, i.e. then

.1 and y -

 "W

Gn (and OUTPUT

X / {Uex (t) - UCM Gs -2 UCM Go I

In the second cycle, the switching element 15 connects the terminals of the resistors 5 and 6, the source of the transistor 2 to the non-inverting input of the unbalance amplifier 1. This changes the sign of the voltage of the UCM applied to the source of the transistor 2, and at the same time the polarity of its output voltage changes. The full-wave rectifier 14 in this cycle inverts the output voltage of amplifier 1, thereby ensuring that the feedback sign is preserved in the negative feedback circuit of amplifier 1.

Then, by analogy with the previous clock, given that the bias voltage of amplifier 1 has the opposite sign

1111 -UBX (O

U10 Gn (willow + UCM)

X I UBX (t) + UCM G5 - 2 UCM Go I

The average value of the output voltage of the amplifier 10 per cycle of the converter

UioCp 0.5 (U110 + uVo). After stating the values of u and U Vo in this formula. decomposition in Taylor series, reducing infinitely small quantities, we get

Uloco

USx (t). GS

 Wed Uewx Gn After averaging the voltage of the Uio filter 7 low frequencies over the period of the signal T:

U

out

-1

45 Designating K V Gs / Gn. will get

Willow ulx (t) dt

Thus, the output voltage of the device is proportional to the rms value of the input alternating voltage.

Claims (1)

Invention Formula The linear converter of the square root of the alternating voltage, containing the first and second field-effect transistors, the gates of which are combined, the first and second resistors, the first terminals of which are connected to the source the first field-effect transistor, the drain of the second field-effect transistor is connected to the input terminal of the device, and the source is connected to the output terminal of the device through a series-connected second inverting amplifier with a third resistor in the feedback circuit, and a low-pass filter whose output is connected to the second terminal of the second resistor through the first inverting amplifier, the input of the third inverting amplifier is connected to the input terminal of the device, and the output to the input of the second inverting amplifier through the fourth resistor, amplify Only the spread, fifth and sixth resistors, the first pin of the fifth resistor is connected to the common bus of the device, characterized in that in order to increase the conversion accuracy with small signals having a constant component, a full-wave rectifier is inserted into it, and a pulse generator, the output of which is connected to the control input of the switching element whose input is connected to the source of the first field-effect transistor, the first output to the inverting input of the unbalance amplifier and the second output of the fifth resistor, and the second output is to the non-inverting input of the unbalance amplifier and through the sixth resistor to the common bus of the device, the input of the half-wave rectifier is connected to the output of the unbalance amplifier, and the output to the field-effect transistor gates, the drain of the first field-effect transistor is connected to the output of the low-pass filter, the second terminal of the first resistor is connected to the input terminal of the device.