RU2394360C1 - Cascode differential amplifier with increased input resistance - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: cascode differential amplifier (CDA) includes input parallel-balance cascade (PBC) (1) having the first (2) and the second (3) inputs, the first (4) and the second (5) current outputs connected to emitters of first (6) and second (7) output transistors (T) the bases of which are combined and connected to offset voltage source (OVS) (8), and collectors are connected to load circuit (9), additional current divider (CD) (10) having the main input (11), as well as first (12) and second (13) outputs connected to the appropriate first (2) and second (3) PBC (1) inputs. PBC (1) includes the first (12) additional current output cophasal with current output (4), second (13) additional current output cophasal with current output (5); at that, current outputs (12) and (13) are connected to emitter of the first additional T (14) the base of which is connected to OVS (8), and collector is connected to emitter of second (15) additional T; base of T (15) is connected to input (16) of auxiliary current mirror (17) the output of which is connected to input (11) of CD (10).

EFFECT: increasing input resistance.

5 cl, 11 dwg

Description

The invention relates to the field of radio engineering and communications and can be used as a device for amplifying analog signals of sensors with high internal resistance, in the structure of analog microcircuits for various functional purposes (for example, operational amplifiers, broadband and selective amplifiers, filters, etc.).

In modern electronics, cascode differential amplifiers (CDA) based on parallel-balanced cascades are used. Such CDFs are the basis of many broadband amplifiers, phase splitters, analog voltage multipliers, frequency doublers, etc. [1-16].

The closest prototype of the claimed device of figure 1 is the CDA, presented in US patent No. 4.843.342 fig. 1. It contains an input parallel-balanced stage 1 having first 2 and second 3 inputs, first 4 and second 5 current outputs connected to emitters of the first 6 and second 7 output transistors, the bases of which are combined and connected to a bias voltage source of 8, and the collectors are connected to the load circuit 9, an auxiliary current divider 10, having a main input 11, as well as the first 12 and second 13 outputs associated with the corresponding first 2 and second 3 inputs of the input parallel-balanced stage 1.

A significant drawback of the known device (Fig. 1) is that it has a relatively small input impedance for an alternating signal, which substantially depends on the current gain of the base (β) of the input transistors (VT1, VT2) and their static mode (I ₀ ) common emitter circuit:

- сопротивления эмиттерных переходов входных транзисторов VT1 и VT2 каскада 1;Where

- resistance of the emitter junctions of the input transistors VT1 and VT2 of cascade 1;

φ _t ≈26 mV - temperature potential;

I _er = 0.5I ₀ is the emitter current of the input transistors.

To increase R _BX, you have to choose a micro mode for the input transistors of the CDU. However, in this case, the voltage gain of the KDU degrades:

where R _n.Eq - equivalent load resistance KDU.

в известных КДУ может также применяться местная отрицательная обратная связь (в эмиттеры VT1, VT2 вводятся резисторы). Однако при этом ухудшаются другие параметры КДУ -коэффициент усиления по напряжению, напряжение смещения нуля, коэффициент подавления помехи по питанию, ослабление синфазных сигналов и др.For increase

In well-known CDDs, local negative feedback can also be used (resistors are introduced into the emitters VT1, VT2). However, at the same time, other KDU parameters deteriorate - voltage gain, zero bias voltage, power supply noise reduction coefficient, common mode signal attenuation, etc.

Thus, the generalized indicator of the quality of remote control - the product K _y R _BX = Q does not depend on the static mode and can be improved in known devices only at the cost of increasing β transistors and R _n.equiv :

The main objective of the invention is to increase the input impedance R _BX without impairing K _y and current consumption of the CDU. In general, this allows to improve the generalized indicator of quality Q. An additional goal is to reduce the static input currents of the CDU.

This goal is achieved in that in the cascode differential amplifier of Fig. 1, containing an input parallel-balanced stage 1 having first 2 and second 3 inputs, first 4 and second 5 current outputs associated with emitters of the first 6 and second 7 output transistors, base which are combined and connected to a bias voltage source 8, and the collectors are connected to the load circuit 9, an auxiliary current divider 10 having a main input 11, as well as the first 12 and second 13 outputs associated with the corresponding first 2 and second 3 inputs of the input pair the power-balanced stage 1, new elements and connections are provided - the input parallel-balanced stage 1 contains the first 12 additional current output, in phase with the first 4 main current output, the second 13 additional current output, in-phase with the second 5 main current output, the first 12 and the second 13 additional current outputs are connected to the emitter of the first additional transistor 14, the base of which is connected to a bias voltage source 8, and the collector is connected to the emitter of the second 15 additional transistor, the base is W cerned additional transistor 15 is connected to the input 16 of the auxiliary current mirror 17, whose output is connected to the auxiliary input current divider 10 November.

Figure 2 presents a diagram of the inventive device in accordance with claim 1 and claim 2 of the claims.

In the circuit of FIG. 3, FIG. 4, FIG. 5, and FIG. 6, examples of an auxiliary current divider 10 are shown.

Figure 7 shows a particular diagram of the inventive device of figure 2 in accordance with claim 1, claim 2 and claim 5 of the claims.

On Fig presents a diagram of the KDU of Fig.7 without compensation circuits (which corresponds to the KDU prototype) in the computer simulation environment PSpice on models of integrated transistors of FSUE NPP Pulsar, and Fig.9 shows a diagram of the inventive device.

The graphs of Fig. 10 characterize the temperature dependences of the input currents of the KDU of Fig. 8 and the KDU of Fig. 9, from which it follows that the proposed device has more than an order of magnitude smaller static input current.

In Fig.11 shows the frequency dependence of the input resistances of the claimed Fig.9 and the known Fig.8 differential amplifiers, from which it follows that the input impedance of the proposed circuit is almost an order of magnitude greater than the KDU prototype.

The cascode differential amplifier with increased input impedance of FIG. 2 comprises an input parallel-balanced stage 1 having first 2 and second 3 inputs, first 4 and second 5 current outputs connected to emitters of the first 6 and second 7 output transistors, the bases of which are combined and connected with a bias voltage source 8, and the collectors are connected to the load circuit 9, an auxiliary current divider 10 having a main input 11, as well as the first 12 and second 13 outputs connected with the corresponding first 2 and second 3 inputs of the parallel input balanced stage 1. The input parallel-balanced stage 1 contains the first 12 additional current output, common mode with the first 4 main current output, second 13 additional current output, common mode with the second 5 main current output, and the first 12 and second 13 additional current outputs are connected with the emitter of the first additional transistor 14, the base of which is connected to a bias voltage source 8, and the collector is connected to the emitter of the second 15 additional transistor, the base of the second 15 additional transistor is connected on to the input 16 of the auxiliary current mirror 17, the output of which is connected to the input 11 of the auxiliary current divider 10.

In the circuit of FIG. 2, in accordance with claim 2, the current transfer coefficient of the auxiliary current mirror 17 is close to two units.

In the circuit of FIG. 3, in accordance with claim 3, the auxiliary current divider 10 contains first 25 and second 26 resistors, the common node of which is connected to its main input 11, and the second terminals of the resistors are connected to the first 12 and second 13 additional current outputs of the auxiliary current divider 10.

In the circuit of FIG. 4, in accordance with claim 4, the auxiliary current divider 10 contains first 27 and second 28 pn junctions, the common node of which is connected to its main input 11, and the second conclusions pn junctions are connected to the first 12 and second 13 additional current outputs of the auxiliary current divider 10.

In the circuit of FIG. 5, in accordance with claim 5, the auxiliary current divider 10 contains first 29 and second 30 transistors whose emitters are connected to its main input 11, the collector of the second transistor 30 is connected to the first 12, and the collector of the second 29 to the second 13 an additional current output of the auxiliary current divider 10, the base of the first 29 transistor connected to the collector of the second 30 transistor, and the base of the second 30 transistor connected to the collector of the first 29 transistor.

Consider the operation of the remote control of Fig.7.

In static mode, the static input current KDU I _BX.1 is determined by the difference between the base current I _b18.19 and the collector current of the transistor 30:

where β _18.19 ⁼ β ₁₈ ⁼ β ₁₉ are the current gain of the base of transistors 18 and 19.

In its turn

where K _il2 . ₁₀ = 2 - current transfer coefficient of the current mirror 10;

β ₁₅ - current gain of the base of the transistor 15;

I ₂₂ ⁼ 4I ₀ - the total current of the total emitter circuit of the transistors 18, 19, 20 and 21.

Thus, the static input current of the remote control, Fig.7

Since the transistors 18, 19 and 15 are identical and have the same type of conductivity, they have β ₁₅ = β _18.19 , therefore, the input current of the CDD significantly decreases.

This is the first advantage of the proposed scheme.

The second advantage of the proposed device is that in the circuit of Fig. 7, compensation is provided not only for the static input currents I input ₁ and I _{input 2} , but also their increments i _{input 1} and i _{input 2} . As a consequence, the input resistance of the KDU of Fig. 7 for alternating current is significantly increased. Indeed, with an increase in the voltage u _I at the input Bx.1 relative to the input Bx.2, the base current i _{b18.19 increases} :

Where

r _e18 , r _e20 - resistance of the emitter transition of the input transistors 18 and 19 of cascade 1;

φ _t = 25 mV - temperature potential;

- эмиттерный ток транзисторов 18 и 20.

- emitter current of transistors 18 and 20.

therefore

On the other hand, the collector current increments of transistors 29 and 30

where r _e29 = r _e30 - resistance of the emitter junctions of transistors 29 and 30.

Moreover

where I ₁₁ = K _i12.10 I _b.15 = 2I _b.15 - the output current of the current mirror 10;

To _i12.1 ≈2 is the current gain of the current mirror 10;

I _b.15 - base current of the transistor 15.

In this way,

where β ₁₅ - current gain of the base of the transistor 15.

Therefore, the total input current of the KDU and its input differential conductivity

In the KDU prototype of figure 1, the input conductivity

Therefore, in the claimed remote control input resistance increases in N _y times, where

The theoretical conclusions obtained above are confirmed by the simulation results of the known and proposed circuits in the PSpice environment on models of integrated transistors of the Federal State Unitary Enterprise NPP Pulsar (Fig. 10, Fig. 11). Moreover, the claimed KDU has almost two orders of magnitude higher input impedance. This result is provided without deterioration of other parameters of the CDD. In addition, the static input currents of the claimed KDU and their drift are significantly less than in the circuit of the KDU prototype (figure 10).

To ensure a high degree of compensation of the input currents of the KDU of Fig. 2 and its input conductivity, it is necessary for transistors 15 and 18, 19 to have β ₁₅ = β _18.19 . Since β depends on the collector-base voltage of transistors 15 and 18, 19 (20, 21) , then due to the special construction of the current mirror 17, it is possible to create U _kb.15 ≈U _kb.18.19 , which further increases the efficiency of the claimed circuit in terms of the received R _BX and I _{input 1} .

BIBLIOGRAPHIC LIST

1. US patent application No. 2002/0053935.

2. US Patent No. 5,767.741.

3. US Patent No. 5.55.512.

4. US patent No. 6.111.463.

5. US Patent No. 4,498.053 fig.6.

6. US patent No. 4.288.707 fig.2.

7. US Patent No. 5,065.112 fig. 3.

8. US patent No. 4.721.920.

9. US patent No. 5.521.544 fig.6.

10. US patent No. 5.256.984.

11. US patent No. 5.389.893 fig. 5.

12. US Patent No. 4,439,696 fig. 2.

13. A. St. USSR No. 600545.

14. US patent No. 5.914.639.

15. US patent application No. 2004/0251965.

16. US Patent No. 5,774,020.

Claims (5)

1. A cascode differential amplifier with increased input impedance, comprising an input parallel-balanced cascade (1) having first (2) and second (3) inputs, first (4) and second (5) current outputs connected to emitters of the first (6 ) and the second (7) output transistors, the bases of which are combined and connected to a bias voltage source (8), and the collectors are connected to the load circuit (9), an auxiliary current divider (10) having a main input (11), as well as the first ( 12) and second (13) outputs associated with the corresponding first (2) and second (3) inputs go parallel-balanced cascade (1), characterized in that the input parallel-balanced cascade (1) contains the first (12) additional current output, in phase with the first (4) main current output, the second (13) additional current output, in-phase a second (5) main current output, the first (12) and second (13) additional current outputs connected to the emitter of the first additional transistor (14), the base of which is connected to a bias voltage source (8), and the collector is connected to the emitter of the second (15) ) additional transistor, bases and the second (15) additional transistor is connected to the input (16) of the auxiliary current mirror (17), the output of which is connected to the input (11) of the auxiliary current divider (10). 2. A cascode differential amplifier according to claim 1, characterized in that the current transfer coefficient of the auxiliary current mirror (17) is close to two units. 3. The cascode differential amplifier according to claim 1, characterized in that the auxiliary current divider (10) contains the first (25) and second (26) resistors, the common node of which is connected to its main input (11), and the second terminals of the resistors are connected to the first (12) and second (13) additional current outputs of the auxiliary current divider (10). 4. The cascode differential amplifier according to claim 1, characterized in that the auxiliary current divider (10) contains the first (27) and second (28) pn junctions, the common node of which is connected to its main input (11), and the second conclusions pn junctions are connected to the first (12) and second (13) additional current outputs of the auxiliary current divider (10). 5. The cascode differential amplifier according to claim 1, characterized in that the auxiliary current divider (10) contains the first (29) and second (30) transistors, the emitters of which are connected to its main input (11), the collector of the second transistor (30) is connected to the first (12), and the collector of the second (29) to the second (13) additional current output of the auxiliary current divider (10), and the base of the first (29) transistor is connected to the collector of the second (30) transistor, and the base of the second (30) the transistor is connected to the collector of the first (29) transistor.

Images