RU2455756C1 - Cascode differential amplifier with increased amplification ratio - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: cascode differential amplifier with increased amplification ratio contains input differential cascade, output differential cascode, the first and the second auxiliary impedors, the first and the second auxiliary transistors, current-stabilising impedor.

EFFECT: higher limit values of amplification ratio by CDA voltage in case of low-voltage supply.

2 cl, 5 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 of various functional purposes (for example, SiGe-operational amplifiers, microwave amplifiers, comparators, continuous voltage stabilizers, etc.).

In modern microelectronics, classical cascode differential amplifiers (KDUs) with two resistors in the collector circuit of output transistors are used [1-10]. This architecture is the basis of a wide class of analog (analog-digital) devices and is the base for both traditional and new technologies.

The closest in technical essence to the claimed device is the cascode differential amplifier according to the patent of Texas Instruments US 5.461.342, fig.1.

A significant drawback of the well-known KDU, the architecture of which is also present in other amplification stages [1-10], is that under restrictions on the supply voltage (E _p ) characteristic of SiGe technological processes (E _p ≤2.0 ÷ 2.5 C), its voltage gain (K _y ) is small (K _ymax = 10 ÷ 20). This is primarily due to restrictions on the resistances of the collector load resistors, which, due to small E _p, cannot be selected as high resistance. Therefore, to increase K _{y, the} so-called "dynamic loads" (DN) are sometimes used, for example, on bipolar transistors, which require a "loss" of static voltage U _DN = 0.8 ÷ 1.6 V between the source bus to ensure their linear operation power and the output of the day. Moreover, the numerical values of U _ДН are equal to 0.8 V for the simplest dynamic loads, which, unfortunately, have a low output impedance:

where U _Earley - voltage Earley output pnp transistor DN;

I _e = I ₀ is the static current of the emitter pnp of the output transistor DN.

For integrated transistors U _Earley = 20 ÷ 30 V. Therefore, when I ₀ = 1 mA, the use of classical dynamic loads does not allow to obtain high values of K _y . Higher output resistances R _days are realized in Wilson current mirrors or cascode current mirror circuits. However, they only work if the static voltage U _bottom between the terminals of such a dynamic load is more than 2U _eb ≥1.6 V. With a low-voltage power supply this is not acceptable. In addition, not all technical processes (for example, SGB25VD, introduced in Russia) allow the use of pnp transistors. For others, for example, radiation-resistant technologies (NPO Integral, Minsk), the use of pnp transistors is not recommended in conditions of radiation exposure to a microelectronic product.

Thus, at low supply voltages, and especially in those cases where it is necessary to obtain more or less significant amplitudes of the output voltage, the well-known circuit solutions of the CDD are not effective.

The main objective of the invention is to increase the limit values of the gain in voltage KDU at low voltage.

The problem is solved in that in the cascode differential amplifier (Fig. 1), containing the input differential stage 1 with the first 2 and second 3 current outputs, the output differential cascode 4, the first 5 current input of which is connected to the first 2 current output of the input differential stage 1 through the first 6 auxiliary bipolar, and the second 7 current input of the output differential cascode 4 is connected to the second 3 current output of the input differential cascade 1 through the second 8 auxiliary bipolar, the first 9 auxiliary a positive transistor, the collector of which is connected to the second 7 current input of the output differential cascode 4, the second 10 auxiliary transistor, the collector of which is connected to the first 5 current input of the output differential cascode 4, the first 11 current-stabilizing two-terminal connected to the emitters of the first 9 and second 10 auxiliary transistors, new elements and communications are provided - the base of the first 9 auxiliary transistor is connected to the first 2 current output of the input differential stage 1, and the base of the second 10 auxiliary of the transistor is connected to the second 3 current output of the input differential stage 1.

The drawing of figure 1 shows a diagram of the CDA prototype.

A diagram of the inventive device corresponding to claim 1 of the claims is shown in the drawing of figure 2.

The drawing of figure 3 shows a diagram of the CDA in accordance with claim 2, in which the output differential cascode 4 is made on pnp transistors 24, 25 and the current mirror 27.

The drawing of figure 4 shows a diagram of a CDA with a paraphase output, in which the output differential cascode 4 is made on pnp transistors 33, 34 and collector load resistors 35, 36.

. Все транзисторы - TN15S.The graph of Fig. 5 characterizes the frequency dependences of the voltage gain (K _y ) of the CDD (Fig. 2 and Fig. 1) obtained in the computer simulation environment of RSpice on models of integrated transistors of FSUE NPP Pulsar at R ₁₇ = R ₁₈ = 1, 5 kOhm, E _c = 1.5 V, R ₈ = R ₉ = 500 Ohm, I ₁₄ = I ₁₁ = 2 mA,

. All transistors are TN15S.

The cascode differential amplifier with a higher gain (Fig. 2) contains an input differential stage 1 with a first 2 and a second 3 current outputs, an output differential cascode 4, the first 5 current input of which is connected to the first 2 current output of the input differential stage 1 through the first 6 auxiliary two-terminal, and the second 7 current input of the output differential cascode 4 is connected to the second 3 current output of the input differential cascade 1 through the second 8 auxiliary two-terminal, the first 9 auxiliary ny transistor, whose collector is connected to the second 7, current input the output of the differential cascode 4, the second 10 auxiliary transistor whose collector is connected to the first 5 current input the output of the differential cascode 4, the first 11 tokostabiliziruyuschy bipole connected to the emitters of the first 9 and second 10 auxiliary transistors. The base of the first 9 auxiliary transistor is connected to the first 2 current output of the input differential stage 1, and the base of the second 10 auxiliary transistor is connected to the second 3 current output of the input differential stage 1.

In the drawing of FIG. 2, the input differential stage 1 is implemented on transistors 12 and 13, the static mode of which is set by the current source 14. The output differential stage 4 is implemented on transistors 13 and 14, the static mode of which is set on the base circuit by the voltage source 19 (Ec). The collector load in cascode 4 is implemented on resistors 17 and 18 connected to the bus of the positive power supply 20. The emitter circuit of the transistors 12, 13, 9, 10 are connected to the bus 21 of the negative power supply source.

In the drawing of figure 3, the output differential cascode 4 is implemented based on the sources of the reference current 22 and 23, transistors 24 and 26, the static mode of which along the base circuit, is set by the voltage source 26 (Ec). The cascode load is a current mirror 27, the output of which is connected to a buffer amplifier 28.

In the drawing of figure 4, the output differential cascode 4 with a paraphase output is implemented on the basis of reference current sources 31 and 32, transistors 33 and 34, the static mode of which is set by the voltage source Ec along the base circuit. The load of cascode 4 are resistors 35 and 36.

In accordance with claim 2, in the circuit of FIG. 3, the first 29 and second 30 frequency correction elements, for example, capacitors, are included in parallel with the first 6 and second 8 auxiliary bipolar.

Consider the operation of the remote control (figure 2) on alternating current.

A positive change in the input voltage (u _I ) leads to a change in the emitter (i _e ) and collector (i _k ) currents of the transistors 12 and 13:

- сопротивление эмиттерного перехода 1-го транзистора при статическом эмиттерном токе I_эi=I₀;Where

- resistance of the emitter junction of the 1st transistor with a static emitter current I _ei = I ₀ ;

φ _t ≈25 mV - temperature potential.

Therefore, the voltage U ₂₃ between the bases of transistors 9 and 10:

where R ₈ = R ₆ - the resistance of the two-terminal 6 and 8.

Voltage u ₂₃ causes a change in the collector currents of transistors 9 and 10:

.where for the case in question

.

As a result, the emitter and collector currents of transistors 15 and 16:

For current i _k16 and output voltage u output ₂ , the following equations can be written:

Thus, the voltage gain of the proposed remote control (figure 2) is N-times greater than the remote control prototype:

These theoretical conclusions are confirmed by the results of computer simulation (Fig. 5), which show that the proposed amplifier has more than 10 times the best gain with relatively low resistance resistors R17 = R18 = 1.5 kOhm, R6 = R8 = 500 Ohm.

Thus, in the proposed KDU (figure 3) with low-impedance collector load resistors 17 and 18, higher values of the voltage gain are realized.

The inventive scheme is particularly promising for use in microelectronic SiGe products of microwave devices.

Information sources

1. US patent No. 5.461.342, fig. 1.

2. US Patent No. 7.236.011, fig. 4.

3. UK patent No. 1,520.085, cl. NRT, fig. 2.

4. US Patent No. 3,482,177.

5. Patent DE No. 2.418.455.

6. Patent RU No. 2.282.303, fig.2.

7. US Patent No. 5.568.092, fig. 1.

8. US Patent No. 5,440.271, fig. 1.

9. Yu.S. Ezhkov. Handbook of amplifier circuitry. Ed. 2nd. M .: Radiosoft, 2002. - P.142, Fig.6.64.

10. Yu.S. Ezhkov. Handbook of amplifier circuitry. Ed. 2nd. M .: Radiosoft, 2002.- P.227, Fig. 8.51.

Claims (2)

1. A cascode differential amplifier with an increased gain, comprising an input differential stage (1) with first (2) and second (3) current outputs, an output differential cascode (4), the first (5) current input of which is connected to the first (2) the current output of the input differential cascade (1) through the first (6) auxiliary two-terminal, and the second (7) current input of the output differential cascade (4) is connected to the second (3) current output of the input differential cascade (1) through the second (8) auxiliary two-pole , the first (9) an auxiliary transistor whose collector is connected to the second (7) current input of the output differential cascode (4), the second (10) auxiliary transistor whose collector is connected to the first (5) current input of the output differential cascode (4), the first (11 ) a current-stabilizing two-terminal connected to the emitters of the first (9) and second (10) auxiliary transistors, characterized in that the base of the first (9) auxiliary transistor is connected to the first (2) current output of the input differential stage (1), and the base of the second (10) ) pop the auxiliary transistor is connected to the second (3) current output of the input differential stage (1). 2. A cascode differential amplifier with a high gain according to claim 1, characterized in that the first (29) and second (30) frequency correction elements are included in parallel with the first (6) and second (8) auxiliary bipolar.

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