RU2292636C1 - Differential amplifier characterized in enhanced common-mode signal attenuation - Google Patents

Abstract

FIELD: radio engineering, analog signal amplifiers, various analog integrated circuits.

SUBSTANCE: proposed differential amplifier has input transistors 1, 2 with local feedback resistor 3 inserted between their emitters, first and second current mirrors 4 and 5 whose inputs 6,and 7 are coupled with collectors of input transistors 1 and 2 and outputs 8, 9 are connected to outputs 10, 11 of third and fourth current mirrors 12 and 13, respectively; emitters of input transistors 1, 2 are connected to first leads 14, 15 of current-regulating resistors 16, 17 whose second leads 18, 19 are connected to inputs 20, 21 of third and fourth current mirrors 12, 13, respectively; outputs of first and third current mirrors 4 and 12 are connected to first current input 22 of additional current adder 23; outputs 9 and 11 of second and fourth current mirrors 5 and 13 are connected to second current input 24 of current adder 23.

EFFECT: enhanced attenuation constant of input common-mode signal.

2 cl, 9 dwg

Description

The invention relates to the field of radio engineering and communications and can be used as a device for amplifying analog signals in the structure of analog microcircuits for various functional purposes (for example, operational amplifiers (op amps)).

Known schemes of classical differential amplifiers (DEs), implemented on the basis of two input transistors with current-stabilizing resistors in their emitter circuits and a local negative feedback resistor connected between the emitters of the input transistors [1-7]. Such remote controls have become one of the main elements of modern analog microcircuitry and are widely used in the structure of various precision voltage-current converters. A significant drawback of such remote controls is that they have low values of the attenuation coefficient of the input common-mode signal (K _os.sf ), which substantially depends on the resistances of the current-stabilizing resistors.

The closest prototype (figure 1) of the claimed device is a differential amplifier described in patent EP No. 1351381 A1 (aka US Pat. No. 6657465 B2) containing the first 1 and second 2 input transistors, between the emitters of which a local feedback resistor 3 is included , the first 4 and second 5 current mirrors, the inputs of which 6 and 7 are connected to the collectors of the input transistors 1 and 2, and the outputs 8 and 9 are connected to the outputs 10, 11 of the third 12 and fourth 13 current mirrors, the emitter of the first 1 and second 2 input transistors connected to the first conclusions 14 and 15 then costabilizing resistors 16 and 17.

A significant drawback of the known remote control is that it has a low attenuation of the input common-mode signals.

The main objective of the invention is to increase the attenuation coefficient of the input common-mode signals of the remote control when using relatively low-resistance current-stabilizing resistors 16 and 17.

This goal is achieved by the fact that in the differential amplifier of figure 1, containing the first 1 and second 2 input transistors between the emitters which include a local feedback resistor 3, the first 4 and second 5 current mirrors, the inputs of which 6 and 7 are connected to the collectors of the input transistors 1 and 2, and outputs 8 and 9 are connected to outputs 10, 11 of the third 12 and fourth 13 current mirrors, and the emitter of the first 1 and second 2 input transistors are connected to the first terminals 14 and 15 of the current-stabilizing resistors 16 and 17, new elements and connections are introduced - second the conclusions 18 and 19 of the current-stabilizing resistors 16 and 17 are connected to the inputs 20 and 21 of the third 12 and fourth 13 current mirrors, the outputs of the first 4 and third 12 current mirrors are connected to the first 22 current input of the additional current adder 23, and outputs 9 and 11 of the second 5 and the fourth 13 current mirrors are connected to the second current input 24 of the additional adder currents 23.

The diagram of the inventive device in accordance with claim 1 of the claims is shown in figure 2.

Figure 3 shows the claimed remote control in accordance with claim 2. The results of computer simulation of the remote control of FIG. 3 in a PSpice environment with an in-phase input signal on models of integrated transistors of the Federal State Unitary Enterprise NPP “Pulsar” and the parameters of the elements and modes indicated in FIG. 4 are shown in FIGS. 5 and 6. Moreover, the graphs of FIG. 5 are taken with the load resistance of the remote control R _n = 100 kOhm, and the graphs of Fig.6 with R _n = 1 kOhm.

Fig. 7 is a diagram of the remote control of Fig. 3 (Fig. 4) for the case when the inverting current follower 30 (F1) is an ideal amplifying element, i.e. has a current transfer coefficient equal to unity in a wide frequency range (K _i.30 = 1). This allows you to identify the ultimate capabilities of the claimed remote control to attenuate common-mode signals, which are represented by the characteristics of Fig. 8 (at R _n = 100 kOhm) and Fig. 9 (at R _n = 1 kOhm).

Figure 5-9 adopted the following designation of the parameters of the remote control:

K _beats is the transmission coefficient of the differential input voltage of the remote control u _in ;

To _us - the transfer coefficient of the common-mode input voltage u _c .

Moreover, between these parameters and the attenuation coefficient of the input common-mode signals K _OS.sf there is the following relationship:

where u _I - voltage between the inputs of the remote control;

u _c - common-mode input voltage at the inputs of the remote control;

u _o - remote control output voltage (u _o = i _o R _n );

R _n - load resistance connected to the output of the remote control;

S _ss - the steepness of the transmission of remote control by the differential input signal u _I ;

S _ds - the steepness of the transmission of remote control in common mode input signal u _c .

The differential amplifier of figure 2 contains the first 1 and second 2 input transistors between the emitters which include a local feedback resistor 3, the first 4 and second 5 current mirrors, the inputs of which 6 and 7 are connected to the collectors of the input transistors 1 and 2, and the outputs 8 and 9 are connected to the outputs 10, 11 of the third 12 and fourth 13 current mirrors, and the emitter of the first 1 and second 2 input transistors are connected to the first terminals 14 and 15 of the current-stabilizing resistors 16 and 17. The second terminals 18 and 19 of the current-stabilizing resistors 16 and 17 are connected to the inputs 20 and 21 t of the second 12 and fourth 13 current mirrors, the outputs of the first 4 and third 12 current mirrors are connected to the first 22 current input of the additional current adder 23, and the outputs 9 and 11 of the second 5 and fourth 13 current mirrors are connected to the second current input 24 of the additional current adder 23.

In accordance with claim 2 of the claims (FIG. 3), an additional current adder 23 comprises first 25 and second 26 output transistors with integrated bases that are connected to a bias source 27, emitters of the first 25 and second 26 output transistors, which are the first 22 and second 24 current inputs of the additional adder currents 23 are connected with auxiliary current-stabilizing two-terminal 28 and 29, and the collector of the first 25 output transistor is connected to the collector of the second output transistor 26 and the output of the differential amplifier through an inverting current follower 30.

Consider the work of the claimed remote control of figure 2.

If a common-mode voltage u _c = u _c1 = u _{c2 is} applied to the remote control inputs, then alternating current components will appear in resistors 16, 17

- проводимости токостабилизирующих резисторов 16 и 17 соответственно.Where

- conductivity of the current stabilizing resistors 16 and 17, respectively.

These increments of currents i ₁₆ , i ₁₇ , which are equal to the corresponding increments of the currents of the emitters of transistors 1, 2, are transmitted, on the one hand, to inputs 6 and 7 and outputs 8, 9 of current mirrors 4 and 5, and on the other, to inputs 20 and 11, and then the outputs 10, 21 of the current mirrors 12 and 13:

where α _i ≈1 is the current transfer coefficient of the emitter of the i-th transistor.

It should be noted that at nodes 22 and 24, the first subtraction of output mirrors of current mirrors close in magnitude

or

The differences of the output currents i _p1 , i _{p2 of the} current mirrors 12 and 4, 13 and 5, due to the difference in their current transfer coefficients K _i.12 and K _i.4 , as well as K _i.13 and K _i.5 are fed to the inputs of the additional the adder currents 23, in which they are subtracting systematic errors of amplification of the common mode signal. Remote control output current

Therefore, the output voltage of the remote control due to the presence of in-phase signal u _c

Therefore, the transfer coefficient of the common mode signal from the input of the remote control to its output

- коэффициент асимметрии, учитывающий неидентичность резисторов 17 и 16, а также усилений по току со входов 22 и 24 сумматора 23.Where

- the asymmetry coefficient, taking into account the non-identity of the resistors 17 and 16, as well as the current gain from the inputs 22 and 24 of the adder 23.

коэффициент асимметрии принимает единичное значение К_ac=1. Как следствие коэффициент передачи синфазного сигнала будет определяться только разностью близких по величине коэффициентов усиления К_i.12 и К_i.13, K_i.4 и К_i.5, α₁ и α₂. Так как токовые зеркала 12 и 13, 4 и 5 попарно идентичны, выполнены по одинаковым схемам, то поэтому передача синфазного сигнала на выходWith high identity y ₁₇ and y ₁₆ , K _i.23 and

the asymmetry coefficient takes a unit value of K _ac = 1. As a result, the common-mode signal transmission coefficient will be determined only by the difference of the _amplitudes K _i.12 and K _i.13 , K _i.4 and K _i.5 , α ₁ and α _{2 that are} close in magnitude. Since the current mirrors 12 and 13, 4 and 5 are pairwise identical, made according to the same schemes, therefore, the transfer of the common-mode signal to the output

K _sf = R _n y ₁₆ K _i.23 [K _i.12 -K _i.13 + α ₂ K _i.5 -α ₁ K _i.4 ] ≈0.

The difference in current transfer coefficients K _i.12 and K _i.13 , K _i.4 and K _i.5 is caused in real circuits by unequal values of β used by _pnp (12, 13) and npn (4, 5) transistors , as well as unequal values of their static mode in terms of collector-base voltage. It is these reasons that lead to the appearance of current errors i _p1 and i _p2 , which are fed to the inputs 22 and 24 of the additional adder 23. However, the input currents i _p1 = i _{p2 of the} additional amplifier 23 will have almost the same values, because current mirrors 4 and 5, as well as 12 and 13 are pairwise identical.

, α₁=α₂, при котором на выходе дополнительного сумматора 23 будут отсутствовать составляющие, обусловленные входным синфазным сигналом, то есть крутизна преобразования входного синфазного напряжения в выходной ток S_сс=i_вых/u_с будет близка к нулю, а К_ос.сф≫1.As noted above, it is quite simple to ensure equality

, α ₁ = α ₂ , in which at the output of the additional adder 23 there will be no components caused by the input common-mode signal, that is, the steepness of the conversion of the input common-mode voltage to the output current S _cs = i _out / u _s will be close to zero, and K _{os. sf} ≫1.

The transmission coefficient of the differential input voltage of the remote control of figure 2 is determined by the formula

(как это имеет место в ДУ фиг.3), тоIf

(as is the case in the remote control of FIG. 3), then

The above findings are confirmed by the simulation results of the proposed circuits in the PSpice environment using integrated transistor models of the Federal State Unitary Enterprise NPP Pulsar (Moscow). The attenuation coefficient of the in-phase input signal of the remote control of Fig. 4 exceeds the value of K _OS.sf > 10 ⁵ (100 dB) in a fairly wide frequency range - up to 5.6 MHz (Fig. 5), and at low impedance load (Fig. 6) it is greater at 10 ⁷ (140 dB) to a frequency of 1 MHz. It should be noted that these values of K _{os.sf are} much better than similar parameters of the best foreign operational amplifiers.

In addition, a high K _{os.sf was} obtained without using reference current sources in the input stage. This was achieved by ensuring complete symmetry of the remote control and creating additional conditions for the mutual compensation of systematic errors in signal amplification through two identical transmission channels from the remote control inputs to its output.

By improving the circuitry of the inverting current repeater 30 (Figs. 3 and 4) - approximating its current gain to unity in a wide frequency range, in the inventive device it is possible to obtain high K _OS.sf (100 dB) up to a frequency of 26 MHz.

In the considered remote control scheme, a high degree of parametric compensation of the influence of temperature and radiation on the emf is also provided. zero bias due to the bias of the input and output characteristics of the transistors.

Information sources

1. Polonnikov D.E. Operational amplifiers: principles of construction, theory, circuitry. - M., 1983. - 216 p. - p. 156 fig. 4.25.

2. US Patent No. 4,131,809, H 03 FK.

3. US patent No. 33323070, H 03 F 3/45.

4. EP patent No. 1351381, A1, H 03 F 3/30.

5. US patent No. 5365191, H 03 F 3/45.

6. US patent No. 4511852, H 03 F 3/45.

7. US patent No. 6657465, H 03 F 3/45.

Claims (2)

1. A differential amplifier containing the first (1) and second (2) input transistors between which emitters includes a local feedback resistor (3), the first (4) and second (5) current mirrors, the inputs of which (6) and (7) ) are connected to the collectors of the input transistors (1) and (2), and the outputs (8) and (9) are connected to the outputs (10), (11) of the third (12) and fourth (13) current mirrors, and the emitter of the first (1 ) and the second (2) input transistors are connected to the first terminals (14) and (15) of the current-stabilizing resistors (16) and (17), characterized in that the second terminals (18) and (19) are current-stabilizing their resistors (16) and (17) are connected to the inputs (20) and (21) of the third (12) and fourth (13) current mirrors, the outputs of the first (4) and third (12) current mirrors are connected to the first (22) current the input of the additional current adder (23), and the outputs (9) and (11) of the second (5) and fourth (13) current mirrors are connected to the second current input (24) of the additional current adder (23). 2. The device according to claim 1, characterized in that the additional current adder (23) contains the first (25) and second (26) output transistors with integrated bases that are connected to the bias source (27), emitters of the first (25) and second (26) output transistors, which are the first (22) and second (24) current inputs of the additional current adder (23), are connected with auxiliary current-stabilizing two-terminal devices (28) and (29), and the collector of the first (25) output transistor is connected to the collector of the second output transistor (26) and differential output preamplifier through an inverting current follower (30).

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