RU2321158C1 - Cascode differential amplifier - Google Patents

Abstract

FIELD: radio engineering and communications, possible use as device for amplification of analog signals, in the structure of analog microchips of various functional purposes (for example, in operational amplifiers, comparators).

SUBSTANCE: cascode differential amplifier contains input parallel-balanced cascade (1) with differential inputs (2,3), first, second, third and fourth output transistors (4-7), bases of which are combined. Combined emitters of output transistors (4,5) are connected to first output (8) of cascade (1) and through first current-stabilizing dipole (9) are connected to bus (10) of first power supply, combined emitters (6,7) are connected to second output (11) of cascade (1) and through first current-stabilizing dipole (12) are connected to bus (10). Load circuit (16) is coupled between collectors of transistors (5,6) and bus (15) of second power supply. Additional transistor (17) is added to the circuit, base of which is connected to bus (18) of shifting voltage supply, collector is connected to combined bases of transistors (4-7), and emitter is connected to combined collectors of transistors (4,7), and through additional current-stabilizing dipole (19) is connected to bus (15) of second power supply, while as first and second current-stabilizing dipoles (9,12) resistors are used.

EFFECT: increased coefficient of weakening of input cophased signal.

11 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, operational amplifiers (op amps), comparators).

Known circuits of the so-called “bent” cascode differential amplifiers (ДУ) on n-pn and pnp transistors [1-35], which became the basis of more than 20 serial operational amplifiers manufactured as foreign (NA2520, NA5190, AD797, AD8631, AD8632, OP90, etc.), as well as by Russian (154UD3, etc.) microelectronic companies. Due to the high popularity of such a remote control architecture, over 200 patents have been issued for their modification for leading manufacturers of microelectronic products. The present invention relates to this subclass of devices.

The closest prototype (figure 1) of the claimed device is the cascode differential amplifier (CDA) described in US patent No. 4390850, containing an input parallel-balanced cascade 1 with differential inputs 2 and 3, the first 4, second 5, third 6 and fourth 7 output transistors whose bases are combined, and the combined emitters of the first 4 and second 5 output transistors are connected to the first 8 output of the input parallel-balanced stage 1 and connected through the first current-stabilizing two-terminal 9 to the bus of the first power source 10, the combined emitters of the third 6 and fourth 7 output transistors are connected to the second output 11 of the input parallel-balanced stage 1 and through the second current-stabilizing two-terminal 12 are connected to the bus of the first 10 power supply, and between the collectors 13 and 14 of the second 5 and third 6 output transistors and the bus of the second the power source 15 is connected to the load circuit 16.

A significant drawback of the known KDU (Fig. 1) is that it has a relatively small attenuation coefficient of the input common-mode signal (K _os.sf ), which negatively affects the errors of non-inverting decision amplifiers and comparators based on it. To a large extent, this drawback is manifested when the static mode of the input parallel-balanced stage is established using the current-stabilizing resistor R ₀ (Fig. 1).

The main objective of the invention is to increase the attenuation coefficient of the input common-mode signal when performing current-stabilizing two-terminal devices 9 and 12 in the form of resistors. In this case, the circuit implements the limit values of the range of variation of the input common-mode signal, unattainable with other options for their construction. Moreover, the increase in K _{OSF is} provided with a fairly wide range of input parallel-balanced stages (both on bipolar and field effect transistors, with transistor current sources and without transistor current sources, according to the scheme of differential voltage-current converters, etc. .).

This goal is achieved in that in the cascode differential amplifier of figure 1, containing an input parallel-balanced stage 1 with differential inputs 2 and 3, the first 4, second 5, third 6 and fourth 7 output transistors, the bases of which are combined, and the combined emitters of the first 4 and the second 5 output transistors are connected to the first 8 output of the input parallel-balanced stage 1 and through the first current-stabilizing two-terminal 9 connected to the bus of the first power source 10, the combined emitters of the third 6 and fourth 7 output one transistor connected to the second output 11 of the input parallel-balanced stage 1 and through the second current-stabilizing two-terminal 12 connected to the bus of the first 10 power supply, and between the collectors 13 and 14 of the second 5 and third 6 output transistors and the bus of the second power source 15 is connected to the load circuit 16 new connections are provided - an additional transistor 17 is introduced into the circuit, the base of which is connected to the bias voltage source bus 18, the collector is connected to the combined bases of the first 4, second 5, third 6 and fourth 7 output transistors, and the emitter is connected to the combined collectors of the first 4 and fourth 7 output transistors and through an additional current-stabilizing two-terminal 19 connected to the bus of the second power source 15, and resistors are used as the first 9 and second 12 current-stabilizing two-terminals.

The amplifier circuit of the prototype is presented in figure 1. Figure 2 presents a diagram of the inventive device in accordance with the claims. Figure 3 shows the remote control corresponding to figure 2 for the case when a common bus is used as the bus of the bias voltage source 18.

Figure 4 shows an example of building a push-pull differential amplifier based on the CDA of figure 2.

In Fig.5 and Fig.6 shows a diagram of the known (Fig.5) and the claimed (Fig.6) devices in a computer simulation environment PSpice, and Fig.7 is the frequency dependence of the attenuation coefficient of the input common-mode signals K _os.sf compared _CDA .

The differential amplifier of figure 2 contains an input parallel-balanced stage 1 with differential inputs 2 and 3, the first 4, second 5, third 6 and fourth 7 output transistors, the bases of which are combined, and the combined emitters of the first 4 and second 5 output transistors are connected to the first 8 by the output of the input parallel-balanced stage 1 and through the first current-stabilizing two-terminal 9 connected to the bus of the first power source 10, the combined emitters of the third 6 and fourth 7 output transistors are connected to the second output 11 input parallel parallel-balanced stage 1 and through a second current-stabilizing two-terminal 12 connected to the bus of the first 10 power supply, and between the collectors 13 and 14 of the second 5 and third 6 output transistors and the bus of the second power source 15 is connected to the load circuit 16. An additional transistor 17 is introduced into the circuit , the base of which is connected to the bias voltage source bus 18, the collector is connected to the combined bases of the first 4, second 5, third 6 and fourth 7 output transistors, and the emitter is connected to the combined collectors of the first of the 4th and fourth 7th output transistors and through an additional current-stabilizing two-terminal device 19 is connected to the bus of the second power supply 15, and resistors are used as the first 9 and second 12 current-stabilizing two-terminal devices.

In the circuit of FIG. 3, the load circuit is based on a reference current source.

In the circuit of figure 4, two CDA are used, corresponding to the claims, but implemented on heterogeneous transistors. Therefore, the digital designations of the symmetric circuit of the CDD in FIG. 4 have the same numbering as in the circuit of FIG. 2.

Consider the operation of the inventive cascode differential amplifier as an example of the analysis of the circuit of figure 2.

In the inventive device of figure 2, in the presence of an in-phase component of the signals u _c2 = u _c3 = u _s , the current in the common emitter circuit of the output stage 1 and the currents in the output circuit 8 and 11 change:

where y ₀ = R ₀ ^-1 is the equivalent conductivity in the common emitter circuit of the input stage 1.

For the currents of the emitter, collector and base of transistors 4-7, the following relationships are true:

where β ₁ >> 1 is the static current gain of the base of the i-th transistor.

From formulas (3) ÷ (11), an important conclusion follows that all the currents of transistors 4-7 in the circuit of figure 2 are determined by the current through the two-terminal network 19 and are not dependent on the resistances of the resistors 9 and 12 and the output currents I ₈ , i ₈ , I ₁₁ , i _{11 of the} input stage 1, where I ₈ , I ₁₁ , i ₈ , i ₉ are the static values of the output currents of the input stage 1 and their increments. Moreover, for the circuit of figure 2, the current through the two-terminal network 19

where E _c is the voltage of the bias source 18;

U _eb = 0.7 V - voltage emitter-base of the transistor 17.

For the circuit of figure 3, the current I ₁₉ does not depend on E _c and U _eb .

In this case, the voltage drop across the resistors 9 and 12 is recommended to be selected within

The analysis shows that in the inventive scheme, the increments of the output currents i ₈ and i _{11 of the} input stage 1, due to the common-mode signal at the outputs 2 and 3 of the CDU, are not transmitted to its output. Moreover

From this it follows that the transfer coefficient of the common-mode signal from the input of the CDA to the output in the claimed circuit is significantly reduced

Since the gain by the differential signal of the compared KDUs is the same (K _y ), it follows that in the proposed scheme, K _OS.sf significantly improves, since

These theoretical conclusions confirm the results of computer modeling of the compared CDDs. In the proposed scheme, K _{os.sf is} increased by 70 dB, that is, more than a thousand times.

Literature

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Claims (1)

A cascode differential amplifier comprising an input parallel-balanced stage with differential inputs, first, second, third and fourth output transistors, the bases of which are combined, the combined emitters of the first and second output transistors connected to the first output of the input parallel-balanced stage and through the first current-stabilizing two-terminal device connected to the bus of the first power source, the combined emitters of the third and fourth output transistors are connected to the second output of the input parallel the flax-balanced cascade and through the second current-stabilizing two-terminal are connected to the bus of the first power source, and a load circuit is connected between the collectors of the second and third output transistors and the bus of the second power source, characterized in that an additional transistor is inserted into the circuit, the base of which is connected to the voltage source bus bias, the collector is connected to the combined bases of the first, second, third and fourth output transistors, and the emitter is connected to the combined collectors of the first and fourth and second output transistors via a further two-pole tokostabiliziruyuschy connected with the second power supply bus, wherein as the first and second tokostabiliziruyuschih two-terminal resistors used.

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