RU2444116C1 - Differential amplifier with low supply voltage - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: differential amplifier with low supply voltage comprises the first and second input transistors, an additional transistor, the first and second current-stabilising dipoles, a load dipole, the first and additional current mirrors.

EFFECT: increased coefficient of DA input cophased signals suppression at relatively low internal resistance of the current-stabilising dipole.

4 cl, 6 dwg

Description

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

There are known schemes of differential amplifiers (DE) with a current-stabilizing two-terminal in the emitter circuit of the input transistors and with an output stage made on a current repeater (current mirror). Remote controls with this architecture have become the basis for the construction of many modern operational amplifiers [1-12], including Op-amps with a rail-to-rail option having a maximum output voltage amplitude close to the supply voltage. However, such remote controls do not have a sufficiently high attenuation of the input common-mode signals (coefficient K _os.sf ) when passive elements (resistors) are used in the common emitter circuit as a current stabilizing two-terminal network, which negatively affects the accuracy of analog interfaces with their use. This is due to the fact that in order to obtain large values of K _OS, it is necessary to choose the resistance of the current-stabilizing resistor at the level of hundreds of kilo-ohms, which creates problems with the static mode at low-voltage power supply (E _p = 1.5 ÷ 5 V). On the other hand, at low supply voltages (E _p = ± 1 V, the use of current-stabilizing resistors is

the only option for constructing a differential cascade, since other schemes for constructing it using bipolar technologies require a supply voltage of at least 1.5 V).

The closest prototype (figure 1) of the inventive device is a differential amplifier described in US patent No. 4264873, fig. 3, containing the first 1 and second 2 input transistors, the emitters of which are combined and connected through the first 3 current-stabilizing two-terminal devices to the first 4 bus of the power supply, the collector of the second 2 input transistor is connected to the input of the first 5 current mirror, matched with the second 6 bus of the power supply, output the first 5 current mirror is connected to the output 7 of the device and through a two-terminal load 8 is connected to the first 4 bus of the power source, and the collector of the first 1 input transistor is connected to the second 6 bus of the power source.

A significant drawback of the known remote control is that it has a low attenuation of the input common-mode signals. First of all, this drawback manifests itself when using 3 resistors or the simplest current sources on Erly low voltage transistors as current-stabilizing two-terminal devices, which have a small output resistance (about 30-60 kOhm) at milliamp currents.

The main objective of the invention is to increase the attenuation coefficient of the input common-mode signals of the remote control (K _OSF ) with relatively small internal resistances of the current-stabilizing two-terminal 3. In this case, the relatively low-resistance resistors (kilo-ohms) can be used as the current-stabilizing two-terminal in low voltage power supply. Nevertheless, this does not significantly affect the numerical values of K _os.sf.

The problem is solved in that in the differential amplifier of Fig. 1, containing the first 1 and second 2 input transistors, the emitters of which are combined and connected through the first 3 current-stabilizing two-terminal devices to the first 4 bus of the power supply, the collector of the second 2 input transistor is connected to the input of the first 5 current the mirror, matched with the second 6 bus power source, the output of the first 5 current mirror is connected to the output 7 of the device and through a two-pole load 8 is connected to the first 4 bus power source, and the collector of the first input transistor is connected to the second 6 bus of the power source, new elements and connections are provided - the combined emitters of the first 1 and second 2 input transistors are connected to the base of the additional transistor 9, the collector of the additional transistor 9 is connected to the first 4 bus of the power source, the emitter of the additional transistor 9 connected to the input of the additional current mirror 10 through the second 11 current-stabilizing bipolar, and the output of the additional current mirror 10 is connected to the output 7 of the device.

In Fig.1 shows a diagram of the remote control prototype. A diagram of the inventive device is shown in figure 2.

In Fig.3 presents a diagram of Fig.1 in a computer simulation Cadance on SiGe models of integrated transistors, and in Fig.4 - of the claimed remote control.

Figure 5 shows the frequency dependence of its gain in voltage of the compared schemes of the remote control of figure 3 and figure 4.

In Fig.6 shows the results of computer modeling of the frequency dependence of K _OSF compared schemes of _{Fig.3 and Fig.4} .

The differential amplifier of figure 2 contains the first 1 and second 2 input transistors, the emitters of which are combined and connected through the first 3 current-stabilizing two-terminal devices to the first 4 bus of the power supply, the collector of the second 2 input transistor is connected to the input of the first 5 current mirror, matched with the second 6 bus of the source power supply, the output of the first 5 current mirror is connected to the output 7 of the device and is connected via the bipolar load 8 to the first 4 bus of the power source, and the collector of the first 1 input transistor is connected to the second 6 th power bus. The combined emitters of the first 1 and second 2 input transistors are connected to the base of the additional transistor 9, the collector of the additional transistor 9 is connected to the first 4 bus of the power supply, the emitter of the additional transistor 9 is connected to the input of the additional current mirror 10 through a second 11 current-stabilizing two-terminal device, and the output of the additional current mirror 10 is connected to the output 7 of the device.

In Fig. 2, in accordance with claim 2, the first 3 and second 11 current-stabilizing two-terminal devices are made in the form of resistors with approximately the same resistances, and the current transfer coefficient of the first 5 current mirror is close to unity, and the additional current mirror 10 is in two times less.

In addition, in Fig. 2, in accordance with claim 3 of the claims, the first 3 and second 11 current-stabilizing two-terminal devices are made in the form of resistors, the resistance of the first 3 current-stabilizing resistor can be half the resistance of the second 11 current-stabilizing two-terminal network, and the transmission coefficient the current of the first 5 and an additional 11 current mirrors are the same. Current mirrors 5 and 10 are made on p-n junctions 13, 14, 16 and transistors 15 and 17. In this case, the current transfer coefficient of the current mirror 10 is 2 times smaller than that of the current mirror 5.

In accordance with paragraph 4 of the claims, the collector of the first 1 input transistor of FIG. 2 is connected to the second 6 bus of the power supply through an additional pn junction 12. This ensures symmetry of the static mode of transistors 1 and 2 in terms of collector-base voltage, which reduces it inaccuracies.

As a bipolar 8, reference current sources on bipolar transistors or resistors can be used.

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

The static control mode of FIG. 2 for u _c1 = u _c2 = 0 is provided by bipolar 3 and 11. Given that the voltage between the input of the current mirror 16 and the second 6 bus power supply is close to the voltage of the emitter-base of transistors 1, 2, 9 (U _e = 0.7 V), it can be found that the static voltage drop at the two-terminal (resistors) 11 and 3 is the same and with the same resistances R11 = R3, the same static currents flow through them.

If the outputs of the remote control of FIG. 2 are supplied with a common-mode voltage u _с1 = u _с2 = u _с , then this causes a change in the currents i _R3 and i _R11 through the two-terminal circuits 3 and 11

where R ₃ , R ₁₁ - the resistance of the two-terminal 3 and 11;

u _Σ is the voltage increment at the emitters of the input transistors 1 and 2, caused by a change in u _c ;

u ₉ ≈u _e9 ≈u _c is the voltage increment at the emitter of transistor 9.

The current i _R3 is divided along the channels between the emitters of transistors 1 and 2, then it is transmitted to the output of the current mirror 5 (i _pt5 ) and creates in the bipolar terminal of load 8 the first component of the output current due to the influence of the in-phase signal u _c

where α ₂ is the current transfer coefficient of the emitter of the second 2 input transistor;

To _i5 - current transfer coefficient of the first current mirror 5 (i _pt10 ).

The second component of the output current (i _pt10 ), due to the influence of u _c and directed in the bipolar load 8 out of phase with the first component i _pt5 , is created by the current mirror 10

where K _i10 is the current transfer coefficient of the current mirror 10.

Therefore, the resulting load current 8 (i ₈ ) and the voltage at the bipolar load 8 (i ₈ R ₈ ), as well as the common-mode signal transfer coefficient K _sf

where R ₃ , R ₁₁ , R ₈ - the resistance of the two-terminal 3, 11, 8.

To _sf - the transfer coefficient of the in-phase signal of the remote control of figure 2,

- коэффициент передачи синфазного сигнала ДУ u_с=u_с1=u_c2 фиг.2 при К_i10=0 (т.е. ДУ-прототипа фиг.1),

- the transfer coefficient of the in-phase signal of the remote control u _c = u _c1 = u _{c2 of figure} 2 at K _i10 = 0 (i.e., the remote control prototype of figure 1),

N _c - coefficient characterizing the effectiveness of compensation

common mode error in the remote control of figure 2.

Moreover

Thus, when choosing R3 = R11, K _i10 = 0.5α ₂ K _i5 = 0.5 in the circuit of FIG. 2, the transmission of the in-phase signal u _c to the output of the remote control decreases by N _s >> 1 time. However, for this it is necessary that the current transfer coefficients of the current mirrors 5 and 6 satisfy the following conditions: K _i10 = 0.5 and K _i5 = 1. These theoretical conclusions are confirmed by the results of modeling the attenuation coefficient of the input common-mode signals of the remote control of Fig. 7:

where K _y is the gain of the differential signal u _in = u _c1 -u _c2 .

Temperature stabilization of the static mode of the claimed remote control can be performed in accordance with patent RU 2386205.

A feature of the circuit of FIG. 2 is a two-channel differential signal transmission u _in = u _c1 -u _c2 through transistors 1, 2 and a current mirror 5, as well as through transistors 1, 9 and a current mirror 10. Moreover, the second transmission channel u _{bx is} characterized by a wide range active operation, close to the voltage drop across the resistor 11, and the range of active operation of the parallel channel on the transistor 1, 2 is close to ± 50 mV. The presence in the architecture of operational amplifiers of such remote controls with a wide range of active operation significantly increases its performance in large signal mode. In addition, the parallel channel increases the voltage gain of the remote control (figure 5).

The above findings are confirmed by the simulation results of the proposed remote control in the Cadance environment using SiGe models of integrated transistors (Fig. 5, Fig. 6). The claimed remote control has higher values of the attenuation coefficient of the input common-mode signals (K _os.sf ) at a relatively low-resistance bipolar 3. However, this circuit is also effective for other options for constructing stabilization circuits of the static mode.

BIBLIOGRAPHIC LIST

1. Patent US 4264873, fig. 3.

2. Patent RU 1748611.

3. Patent WO / 2002/047257.

4. U.S. Patent 7,782,139, fig. 5.

5. Patent JP 154-10221, H03F 3/45.

6. Patent application US 2006/0012432, fig.6.

7. US patent 43664426, fig.2.

8. US patent 4262261.

9. Germany patent 2928841, fig. 3.

10. Patent US 4433302.

11. Patent JP 54-102949 / 98 (5) A21.

12. Patent US 7605658, fig. 4.

Claims (4)

1. A low-voltage differential amplifier containing the first (1) and second (2) input transistors, the emitters of which are combined and connected through the first (3) current-stabilizing two-terminal device to the first (4) bus of the power supply, the collector of the second (2) input transistor connected to the input of the first (5) current mirror, matched with the second (6) bus of the power source, the output of the first (5) current mirror is connected to the output (7) of the device and connected via the load double-pole (8) to the first (4) bus of the power source , and the collector first o (1) the input transistor is connected to the second (6) bus of the power source, characterized in that the combined emitters of the first (1) and second (2) input transistors are connected to the base of the additional transistor (9), the collector of the additional transistor (9) is connected to the first (4) bus of the power source, the emitter of the additional transistor (9) is connected to the input of the additional current mirror (10) through the second (11) current-stabilizing two-terminal device, and the output of the additional current mirror (10) is connected to the output (7) of the device. 2. The low-voltage differential amplifier according to claim 1, characterized in that the first (3) and second (11) current-stabilizing two-terminal devices are made in the form of resistors with approximately the same resistances, and the current transfer coefficient of the first (5) current mirror is close to unit, and an additional current mirror (10) is two times less. 3. The low-voltage differential amplifier according to claim 1, characterized in that the first (3) and second (11) current-stabilizing two-terminal devices are made in the form of resistors, and the resistance of the first (3) current-stabilizing resistor is two times less than the resistance of the second (11) current-stabilizing two-terminal, and the current transfer coefficients of the first (5) and additional (11) current mirrors are the same. 4. The low-voltage differential amplifier according to claim 1, characterized in that the collector of the first (1) input transistor is connected to the second (6) bus of the power source through an additional p-n junction (12).

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