SU1631703A2 - Current amplifier - Google Patents

Abstract

This invention relates to a measurement technique. The purpose of the invention is to improve accuracy by reducing the shear current. The current amplifier contains transistors 1-4, 20-23, transistors 5 and 6 in the diode switching on, current reflectors on transistors 7-18, a bipolar current-supply el-t on resistor 19, a power supply with buses 24 and 25 and a common bus 26. In In this current amplifier, the goal is achieved by the fact that the shear current does not depend on the spread of the coefficients of transistors of different structures, but is determined only by the accuracy of the current reflectors. 1 il.

Description

The invention relates to measuring equipment and automation, can be used in devices of linear amplification of current, voltage, current-voltage converters and is additional to the circuit, St. Ns 1548841.

The purpose of the invention is to increase accuracy by reducing shear current.

The drawing shows a circuit diagram of a current amplifier.

The current amplifier contains the first, second, third, fourth transistors 1-4, the first and second transistors 5.6 in diode switching, the first, second, third, fourth current reflectors on transistors 7-18, a bipolar current-sensing element on the resistor 19, the first, second, third, fourth additional transistors 2023, buses 24, 25 of the power source, a common bus 26.

The current amplifier operates as follows.

To minimize the shear current of the current amplifier, the following groups of transistors must be identical: 4, 21 and 22, 3, 20 and 23; 8, 10, 12 and 14; 7, 9, 11 and 13; 15 and 17, 16 and 18; 1 and 5; 2 and 6.

When power is supplied through the resistor 19 and transistors 7 and 8 in the diode inclusion, a bias current flows (1 _C m), defined by the expression. _ UriMT + Tspit “'CBE.7 U6.3.8 where Opt, U ™ _T are the voltage on the 24, 25 busbars of the power supply, respectively;

ibe.7, U6.3.8 ~ voltage base - emitter of transistors 7 and 8;

R19 is the value of resistor 19.

The same current flows through transistors 10, 12, 14, 11, 9, and 1. Through transistors 20 and 21, current flows from transistors 10, 12, 9, and 11, i.e. 2 · 1 _C m. Through the current sensor of the transistor 1 on the transistor 5 flows the base current of the transistor 20, equal to

I__2 1cm —a--, pp - p - p where Is is the current through transistor 5;

β p - p - p - coefficient p-p-p transistor.

Similarly, a current 1b flows through transistor 6, equal to 2 1cm! B = -o ---------- p η - p - η

Averaged current flows through transistors 1 and 2, i.e.

'1cm | 2 1cm, = SZ1JP__yiggl =

- Icm ί ~ σ ~~ ---- Η -β— - \.

\ D ρ - η - ρ ρ η - ρ - π /

Through the transistor 17, a current flows almost equal to the current of the transistor 15 ·, which is equal to the base current of the transistor 22, i.e.:

1cm <17 = 75 ----------, rp - P - η

1cm) 118 = 7} ---------- · ·

Rp - η - p

The base current of the amplifier stage on transistor 3 is equal to the algebraic sum of the currents of transistors 1 and 17, i.e.

<63 = <17 - h.2 - ~ n ——- ρ η - p - η ^_ * ^cm (- * - ⁿ ~ in —'—) ⁼ \ ρ η - p - η ρ ρ - η - p / _ _ 1cm ____ βρ —η —p 'where the sign indicates that the current flows from the base of the transistor. Similarly, the base current of transistor 4 is equal to the algebraic sum of the currents of transistors 2 and 18, i.e.

<64 - 11.2 118 = ~ 1cm (-β ------ Г -β -------- \ ρ ρ - η - ρ ρ η - ρ - η __1cm _ 1cm βρ - η -. Ρ β η - ρ - η

We determine the quiescent currents through transistors 3 and 4, equal to the product of the base currents of these transistors by their coefficient, i.e.:

- 163 'β p - η - p ⁼ _ 1cm' βρ— η— ρ --75 - I CM:

Pp —n —p = 164 'β n - p - n ⁼ _ Icm ./2 --— pn - p - n - Icm · ρ Π - p - n

It can be seen from this that, despite the different values of the coefficients of the transistors of the p-p-p and p-p-p structures, the current through the transistors 3 and 4 is equal! _With m. Thus, in this device, the shear current does not depend on the coefficients of transistors of different structures. Therefore, with an input current of 1 _VX equal to zero, at the output of the proposed device, the current is almost zero.

The operation of the circuit when exposed to an input signal (Δ 1 _BX t 0) is similar to that described in the prototype. The gain of the flow with an open feedback loop of the device Κι as well as in the prototype is equal to _{K |} _ "1 · β3 + α ₂ · β4 where" 1, "2 - current gain of the transistors 1 and 2., respectively;

/? s. βύ, are the current gain of the transistors 3 and 4, respectively.

Compare the shear currents (1 _C d _V ) of the prototype and the proposed device. In the general case, the shear current is equal to the sum of two components due to the inequality of the coefficients transistors of different structures of the amplification stage (1sdv) and the error of the current reflectors of the bias stage at transistors 8, 10, 12, 14 and 7, 9, 11, 13, N of the input circuit (I _C dv), i.e.

Mr. G!

1spv ⁼ kdv + 1sdv.

In this device, the shear current (1 _C dv) does not depend on the spread of the coefficients of transistors of different structures, i.e. 1 _With dv = 0, and is determined only by the error of the current reflectors, which is the same as in the prototype.

In addition, the proposed device is characterized by better temperature stability, since the current compensation circuit compensates for the temperature component of 1sdv due to a change in the coefficients from the temperature of the amplifier stage, and improves the dynamic characteristics of the input stage. This is due to a 2-fold decrease in the dynamic input impedance of the circuit due to an increase in the quiescent current flowing through the transistors 1,2, 5,6,20 and 21, and a decrease in the input impedance of the circuit reduces the charge time of the parasitic capacitances of the summing point and, therefore, increases the speed of the described circuit operating in conjunction with the current DAC, characterized by a large value of the output capacitance.

Claims (1)

Claim Amplifier No. 1548841, characterized in that, in order to increase accuracy by reducing the shear current, the third and fourth additional transistors are introduced, having the structure of the fourth and third transistors, the third and fourth current reflectors, the outputs of which are connected to the bases of the third and fourth transistors, respectively, common conclusions - to the collectors of the third and fourth additional transistors, respectively, and the corresponding buses of the power supply, and the inputs - to the bases of the third and fourth additional, respectively transistors, while the first and second current reflectors are made with the first and second additional outputs, the first of which are connected to the outputs of the same current reflectors, and the second outputs are emitters of the fourth and third current reflectors, respectively.