RU2509406C1 - Input stage of high-speed operational amplifier - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: input stage of the operational amplifier comprises first (1) and second (2) input transistors, first (3) and second (4) output transistors, first (5) and second (6) auxiliary transistors, first (7) and second (8) device inputs, first (9) and second (10) forward-biased p-n junctions, a first (11) current-stabilising two-terminal device, current outputs of the device (12), (13), (14), (15), first (16) power supply bus, where between the second (10) p-n junction, connected to the emitter of the second (6) transistor, and a second (17) power supply bus, there is a first (11) two-terminal device connected, between the first (9) p-n junction, connected to the emitter of the first (5) transistor, and the second (17) power supply bus, there is a second (18) two-terminal device connected, between the common node (19) of the first (9) p-n junction and the second (18) two-terminal device, as well as the common node (20) of the second (12) p-n junction and the first (11) two-terminal device, there are series-connected third (21) and fourth (22) resistors, the common node (23) of which is connected to the bases of the first (3) and second (4) input transistors.

EFFECT: wider range of active operation of the input stage of the operational amplifier for a differential signal.

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Description

The invention relates to the field of radio engineering and communications and can be used as a device for amplifying analog signals with a wide dynamic range, in the structure of analog microcircuits for various functional purposes (for example, high-speed operational amplifiers (OA)).

Known circuits of the input stages of the op-amp, made in the form of differential amplifiers (DE) on n-p-n- and p-n-p-transistors with the so-called "architecture of the input stage of the operational amplifier µA741" [1-30]. Over 50 patents have been issued for their modifications for leading microelectronic companies in the world. Differential amplifiers of this class, along with a typical parallel-balanced cascade

[29-30], have become the main amplifier element of many analog interfaces. This is due to the fact that in such remote control the input capacitance is minimized due to the absence of the Miller effect. The present invention relates to this subclass of devices.

The closest prototype (figure 1) of the claimed device is the input stage of a high-speed operational amplifier according to the patent US 4.901.031, containing the first 1 and second 2 input transistors, the emitters of which are connected to the emitters of the corresponding first 3 and second 4 output transistors with integrated bases, the first 5 and second 6 auxiliary transistors, the bases of which are connected to the corresponding bases of the first 1 and second 2 input transistors and are connected to the corresponding first 7 and second 8 inputs of the device, the first 9 and second 10 self-biased pn junctions included in the emitters of the corresponding first 5 and second 6 auxiliary transistors, the first 11 current-stabilizing two-terminal devices, the current outputs of the device 12, 13, 14, 15 associated with the collectors of the first 1 and second 2 input transistors, as well as the collectors of the first 3 and the second 4 output transistors, and the collectors of the first 5 and second 6 auxiliary transistors are connected to the first 16 bus power source.

A significant drawback of the known remote control is that it has a relatively narrow dynamic range (U _gr ) of linear amplification of differential signals (U _vx.max <U _gr ≈100 ÷ 150 mV). As shown in [31], this circumstance is the main reason for the low performance of modern operational amplifiers, due to the nonlinear operation mode of the input stage of the op amp. Moreover, for most opamps with a high-impedance node and one correcting capacitor, the maximum slew rate of the output voltage

$${\upsilon }_{\mathrm{at}sx}=2\pi f_{\mathrm{from}R}{U}_{gR},\left(\mathrm{one}\right)$$

where f _cf is the unit gain frequency (cutoff frequency) of the adjusted op-amp;

U _gr is the voltage limiting the pass-through characteristic i _out = f (u _in ) of the input stage (for classical remote control U _gr = 50 ÷ 100 mV). From (1) it follows that the increase u _out can be achieved in two qualitatively different ways:

1. An increase in the range of active operation of the input remote control (U _gr ) without changing the slope of the conversion of the input voltage to the output currents of the remote control;

2. An increase in f _cf due to an improvement in the frequency properties of transistors, which is associated primarily with the use of higher-frequency manufacturing processes (SG25VD, SG25H1, SG25RH, etc.). The inventive input stage of the op-amp solves the problem of increasing speed by increasing (without changing the slope) more than an order of magnitude of the linear range U _gr = 1 ÷ 2B.

Thus, the main objective of the invention is to expand the range of active operation of the input stage of the op-amp for a differential signal - obtaining U _gr >> 100 mV.

The problem is achieved in that the input stage of a high-speed operational amplifier containing the first 1 and second 2 input transistors, the emitters of which are connected to the emitters of the corresponding first 3 and second 4 output transistors with integrated bases, the first 5 and second 6 auxiliary transistors, the bases of which are connected to the corresponding bases of the first 1 and second 2 input transistors and connected to the corresponding first 7 and second 8 inputs of the device, the first 9 and second 10 forward biased pn junctions included emitters of the corresponding first 5 and second 6 auxiliary transistors, the first 11 current-stabilizing two-terminal, current outputs of the device 12, 13, 14, 15 connected to the collectors of the first 1 and second 2 input transistors, as well as the collectors of the first 3 and second 4 output transistors, and collectors the first 5 and second 6 auxiliary transistors are connected to the first 16 power supply bus, characterized in that between the second 10 forward biased pn junction included in the emitter of the second 6 auxiliary transistor and the second 17 bus the power source includes the first 11 current-stabilizing two-terminal, between the first 9 forward biased pn junction included in the emitter of the first 5 auxiliary transistor, and the second 17 bus power supply includes a second 18 current-stabilizing two-terminal, between the common node 19 of the first 9 forward biased pn junction and the second 18 current-stabilizing the two-terminal network, as well as the common node 20 of the second 12 forward biased pn junction and the first 11 current-stabilizing two-terminal network, the third 21 and fourth 22 additional res Storey, common node 23 which is connected to the bases of the first 3 and second 4 input transistors.

The amplifier circuit of the prototype is presented in figure 1. Figure 2 shows the inventive device in accordance with the claims.

Figure 3 shows a possible architecture of a high-speed operational amplifier with the proposed input stage.

In Fig.4 shows a diagram of the remote control prototype of Fig.1 in a computer simulation environment PSpise on models of integrated transistors of FSUE NPP Pulsar.

5 shows dependence of the difference output currents (I (out1) -I (out2 )) and (I (out3) -I (out4 ))- 4 prototype control of the input voltage u _Rin.

Figure 6 shows the dependence of the absolute values of the output currents I (out1) and I (out2)-4 prototype control of the input voltage u _Rin. The dependence of the output currents I (out3) and I (out4) of the remote control prototype of FIG. 4 on the input voltage u _in is shown in FIG. 7.

On Fig shows a diagram of the claimed remote control of figure 2 in the environment of computer simulation PSpise on the models of integrated transistors FSUE NPP Pulsar, and figure 9 - figure 12 - dependence of the differences of the output currents (I (out1) -I (out2) ) and (I (out3) -I (out4)) from the input voltage u _{in the} remote control of Fig. 8 for different values of the resistances of the additional resistors 21, 22 (R _var ).

In Fig.13 shows the dependence of the absolute values of the output currents I (out1) and I (out2) of the claimed control of Fig.8 from the input voltage u _in with the resistances of the additional resistors 21, 22 R _var = 200 Ohms, and Fig.14 - dependence of the output currents I (out3) and I (out4) of the claimed remote control of Fig. 8 from the input voltage u _in with the resistances of additional resistors 21, 22 R _var = 200 Ohms.

Figure 15 shows the absolute values of the output currents I (out1) and I (out2) of the claimed controller 8 of the input voltage u at _Rin additional resistances of resistors 21, 22 R _var = 1 kohm, and 16 - the dependence of output currents I (out1) and I (out2) of the claimed remote control of Fig. 8 from the input voltage u _in with the resistances of additional resistors 21, 22 R _var = 1 kOhm on an enlarged scale.

On Fig presents the dependence of the absolute values of the output currents I (out3) and I (out4) of the claimed remote control from the input voltage u _in at R _var = 1 kOhm, and on Fig - dependence of the output currents I (out3) and I (out4 ) of the claimed remote control from the input voltage u _in at R _var = 1 kOhm on an enlarged scale.

The input stage (DU) of the high-speed operational amplifier of figure 2 contains the first 1 and second 2 input transistors, the emitters of which are connected to the emitters of the corresponding first 3 and second 4 output transistors with integrated bases, the first 5 and second 6 auxiliary transistors, the bases of which are connected to the corresponding bases of the first 1 and second 2 input transistors and connected to the corresponding first 7 and second 8 inputs of the device, the first 9 and second 10 forward biased pn junctions included in the emitters corresponding to the first 5 and the second 6 auxiliary transistors, the first 11 current-stabilizing bipolar, the current outputs of the device 12, 13, 14, 15 associated with the collectors of the first 1 and second 2 input transistors, as well as the collectors of the first 3 and second 4 output transistors, and the collectors of the first 5 and second 6 auxiliary transistors are connected to the first 16 bus power source. Between the second 10 forward biased pn junction included in the emitter of the second 6 auxiliary transistor and the second 17 bus of the power supply, the first 11 current-stabilizing bipolar is connected, between the first 9 forward biased pn junction included in the emitter of the first 5 auxiliary transistor and the second 17 bus of the power source the second 18 current-stabilizing two-terminal network is connected, between the common node 19 of the first 9 forward biased pn junction and the second 18 current-stabilizing two-terminal network, as well as the general node 20 of the second 12 forward biased pn-junction the course and the first 11 of the current-stabilizing two-terminal are sequentially connected to the third 21 and fourth 22 additional resistors, a common node 23 of which is connected to the bases of the first 3 and second 4 input transistors.

In Fig. 3, the claimed input stage of Fig. 2 (24) is included in the structure of a high-speed op-amp, which contains additional current mirrors 25, 26, an output buffer 27, and a correction capacitor 28. In this case, the op-amp is covered by 100% negative feedback.

Consider the operation of the inventive device of figure 2.

Due to the fact that the voltage drop across the resistors 21, 22, created by the base currents of transistors 3 and 4, is small, the static currents of all transistors of the circuit are determined by the currents of the stabilizing two-terminal circuits 18 and 11. Moreover, due to the increase in the area of emitter junctions of transistors 1, 2 3, 4 it is possible at zero input voltage of the remote control to ensure the equality of all emitter currents of the circuit:

$$I_{\mathrm{uh}\mathrm{one}}=I_{\mathrm{<figure-callout\; id="2"\; label="uh"\; filenames="00000009.png,00000010.png"\; state="\{\{state\}\}">uh</figure-callout>}2}=I_{\mathrm{<figure-callout\; id="3"\; label="uh"\; filenames="00000009.png,00000010.png"\; state="\{\{state\}\}">uh</figure-callout>}3}=I_{\mathrm{uh}\mathrm{four}}=I_{\mathrm{<figure-callout\; id="5"\; label="uh"\; filenames="00000009.png,00000010.png"\; state="\{\{state\}\}">uh</figure-callout>}5}=I_{\mathrm{<figure-callout\; id="6"\; label="uh"\; filenames="00000009.png,00000010.png"\; state="\{\{state\}\}">uh</figure-callout>}6}\approx {\mathrm{<figure-callout\; id="0"\; label="I\; uh"\; filenames="00000011.png,00000012.png"\; state="\{\{state\}\}">I\; </figure-callout>}}_{\mathrm{uh}},\left(\mathrm{one}\right)$$

where I ₀ = I ₁₈ = I ₁₁ .

If the voltage at the first 7 input (In1) of the remote control becomes greater than the voltage at the second 8 input of the remote control, then the collector currents of the transistor 1 and 3 increase, and the transistors 2 and 4 decrease. In this case, the input differential voltage u _I "stands out" on the resistors 21 and 22, which leads to an increase in the "opening" voltage between the base of transistor 1 and the base of transistor 3:

$$u_{b\mathrm{one}-3}\approx \frac{{\mathrm{<figure-callout\; id="2"\; label="u\; at\; x"\; filenames="00000009.png,00000010.png"\; state="\{\{state\}\}">u\; </figure-callout>}}_{\mathrm{at}x}}{2}.\left(2\right)$$

Thus collector (output) currents of the transistors 1 and 3 are proportional to the input voltage u in a wide range _Rin:

$${\mathrm{<figure-callout\; id="12"\; label="i"\; filenames="00000009.png,00000015.png"\; state="\{\{state\}\}">i</figure-callout>}}_{12}=i_{\mathrm{fourteen}}\approx \frac{u_{\mathrm{at}x}}{r_{\mathrm{uh}\mathrm{one}}+{\mathrm{<figure-callout\; id="2"\; label="r\; uh"\; filenames="00000009.png,00000010.png"\; state="\{\{state\}\}">r\; </figure-callout>}}_{\mathrm{uh}}+R_{\mathrm{uh}}+\frac{R_{21}}{2{\mathrm{<figure-callout\; id="3"\; label="\beta "\; filenames="00000009.png,00000010.png"\; state="\{\{state\}\}">\beta </figure-callout>}}_3}},\left(3\right)$$

where r _e1 , r _e2 - resistance of the emitter junctions of transistors 1 and 3;

R ₂₁ = R ₂₂ - resistance of the resistors 21 and 22;

β ₃ - current gain of the base of the transistor 3;

Re is the resistance of a low-volume resistor emitter resistor or additional resistor R _d = 10 ÷ 20 Ohm, which is included in some cases in the emitter circuit of transistors 1 and 3 (Fig. 8).

Given that with increasing I _{ei, the} resistances r _e1 and r _e2 significantly decrease, from (3) we can find that for large u _in

$${\mathrm{<figure-callout\; id="12"\; label="i"\; filenames="00000009.png,00000015.png"\; state="\{\{state\}\}">i</figure-callout>}}_{12}=i_{\mathrm{fourteen}}\approx \frac{u_{\mathrm{at}x}}{2\left(R_{\mathrm{uh}}+\frac{R_{21}}{2{\beta }_3}\right)}=u_{\mathrm{at}x}S,\left(\mathrm{four}\right)$$

- крутизна ДУ.Where $$S=\frac{\mathrm{one}}{2\left(R_{\mathrm{uh}}+\frac{{\mathrm{<figure-callout\; id="21"\; label="R"\; filenames="00000010.png"\; state="\{\{state\}\}">R</figure-callout>}}_{21}}{2{\beta }_3}\right)}$$

- the steepness of the remote control.

Equation (4) is valid for the following amplitudes of the input voltages

$$U_{\mathrm{at}x.m\mathrm{but}x}\le U_{gR}=I_0{\mathrm{<figure-callout\; id="21"\; label="R"\; filenames="00000010.png"\; state="\{\{state\}\}">R</figure-callout>}}_{21}=I_0{R}_{22}.\left(5\right)$$

Thus, the range of active operation of the remote control of FIG. 2 is determined by the product (5) and can be selected in accordance with the required values to υ _{out of the} operational amplifier (1). These findings are confirmed by graphs (Fig.9-17), from which it follows that the range of active work of the proposed remote control increases by an order of magnitude in comparison with U _gr remote control prototype.

Thus, the pass-through characteristic i _out = f (u _in ) of the claimed remote control "extends" to the region of high currents (Fig.9-17), significantly exceeding the static currents of the transistors of the remote control. This is typical for transistor cascades of class "AB".

With a negative u _{in the} remote control of _figure 2 works similarly.

The results of computer simulation of the remote control (Fig. 8), presented on the graphs (Figs. 9-17), confirm the theoretical conclusions obtained above.

The proposed remote control can be used in the structure of high-speed operational amplifiers for various functional purposes, as well as in analog microcircuits with a wide range of linear operation.

BIBLIOGRAPHIC LIST

1. US patent No. 3.786.362.

2. US patent No. 4.030.044.

3. US patent No. 4.059.808, Fig.5.

4. US patent No. 4.286.227.

5. Autosvid. USSR No. 375754, H03f 3/38.

6. Autosvid. USSR No. 843164, H03f 3/30.

7. US Patent No. 3,660,773.

8. US Patent No. 4,560,948.

9. RF patent No. 2930041, H03f 1/32.

10. Japanese Patent No. 57-5364, H03f 3/343.

11. Patent of Czechoslovakia No. 134845, cl. 21a ² 18/08.

12. Patent of Czechoslovakia No. 134849, cl. 21a ² 18/08.

13. Czechoslovak Patent No. 135326, cl. 21a ² 18/08.

14. US patent No. 4.389.579.

15. Patent of England No. 1543361, NZT.

16. US patent No. 5.521.552 (figa).

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19. US Patent No. 4,453.134.

20. US patent No. 4.760.286.

21. Autosvid. USSR No. 1283946.

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23. US patent No. 4.389.579.

24. US patent No. 4,453.092.

25. US Patent No. 3,566.289.

26. US patent No. 4.059.808 (figure 2).

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28. US patent No. 4.714.894 (figure 1).

29. Matavkin V.V. High-speed operational amplifiers. - M.: Radio and Communications, 1989.

30. M. Herpy. Analog integrated circuits. - M.: Radio and Communications, 1983, p. 174, Fig. 5.52.

31. Operational amplifiers with direct connection of cascades [Text] / V.I. Anisimov, M.V. Kapitonov, N.N. Prokopenko, Yu.M. Sokolov. - L., 1979. - 148 p.

Claims (1)

The input stage of a high-speed operational amplifier containing the first (1) and second (2) input transistors whose emitters are connected to the emitters of the corresponding first (3) and second (4) output transistors with integrated bases, the first (5) and second (6) auxiliary transistors whose bases are connected to the corresponding bases of the first (1) and second (2) input transistors and are connected to the corresponding first (7) and second (8) inputs of the device, the first (9) and second (10) forward biased pn junctions included to emitters of relevant n the first (5) and second (6) auxiliary transistors, the first (11) current-stabilizing two-terminal device, the current outputs of the device (12), (13), (14), (15) associated with the collectors of the first (1) and second (2) input transistors, as well as collectors of the first (3) and second (4) output transistors, and the collectors of the first (5) and second (6) auxiliary transistors are connected to the first (16) power supply bus, characterized in that between the second (10) direct biased pn junction included in the emitter of the second (6) auxiliary transistor and the second (17) source bus The first (11) current-stabilizing two-terminal device is switched on, between the first (9) forward-biased pn junction included in the emitter of the first (5) auxiliary transistor, and the second (17) current-stabilizing two-terminal device, between the common node ( 19) the first (9) forward biased pn junction and the second (18) current stabilizing bipolar, as well as the common node (20) of the second (12) forward biased pn junction and the first (11) current stabilizing bipolar, the third (21) and fourth (22 ) additional resistors, the common node (23) of which is connected to the bases of the first (3) and second (4) input transistors.

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