JPS6145612A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To increase a transmission conductance without increasing power consumption of the titled circuit by feeding back an output current of one of transistors (TR) to a common emitter via a current mirror circuit. CONSTITUTION:One collector current of a couple of TRs 1, 2 constituting a differential pair is fed to a current feedback circuit 6 by the current mirror circuit 5 so that the current is fed back to the common emitter of the couple of TRs 1, 2. The current being the same value as that fed back to the common emitter is extracted as an output current of the current mirror circuit 5. Then, the current in the common emitter of the TRs 1, 2 is doubled in comparison with the current without any feedback and then the transmission conductance is doubled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a differential amplifier circuit suitable for a low power consumption circuit.

[Technical background of the invention]

FIG. 3 is a circuit diagram showing an example of a conventional differential amplifier, and is described in Kenaroda ``C Basic Circuit'', written by Hideo Tsunoda, published by Tokyo Denki University Press. That is, the common emitters of the transistors 1.2 forming the differential pair receive a current I. It is grounded via a current source 3 that supplies . Torera transistor 1
．． When input signal n from signal source 4 is applied to the base of transistor 1.2, Iotrr 1 is applied from the collector of transistor 1.2.
, l0UT2d force current can be taken out.

In the above circuit, if the potential difference between the two differential inputs formed by the base of transistor 1.2 is Δ■, and the ground current amplification factor of transistor 1.20 is gS, the base of the natural logarithm is e. Iotrrl and IoorIoUTl-□
10 eav-・・・・・・・・・・・・(1) ΔT Here, Boltzmann constant 't'' k The charge of s electron is q1
When the absolute temperature is T, the above vT is expressed by the following formula.

Next, assuming that the transfer conductances of the transistors 71 and 2 are gml and β, respectively, the following equation holds true.

From equations (4) and (5), in order to increase gml and 帥2, the current I of current source 3 must be increased. I had no choice but to make it bigger.

[Problems with background technology]

In recent years, the power consumption of various circuits has been reduced, and the only way to increase the transfer conductance of a differential amplifier like the one described above is to increase the emitter current, which leads to an increase in power consumption. This is a drawback. In particular, since the transfer conductance of a differential amplifier is the most important factor in determining the performance of the amplifier, the above-mentioned drawbacks must be resolved as soon as possible.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above drawbacks, an object of the present invention is to provide a differential amplifier circuit that can obtain a large transfer conductance without significantly increasing power consumption.

[Summary of the invention]

In the present invention, the emitters of a pair of transistors constituting a differential pair are connected to a current source, and an input signal is applied to the bases of these transistors to extract an output current from each collector. In the differential amplifier circuit, a current mirror circuit supplies collector current of one of the pair of transistors, and a current of this current mirror circuit is input, and a corresponding output current is applied to the common emitter of the pair of transistors. The above object is achieved by having a current feedback circuit for feeding back, and having a configuration in which a current having the same magnitude as the current fed back to the common emitter of the pair of transistors is taken out from the current mirror circuit as an output current. It is something to do.

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, in which the same parts as those of the conventional example are denoted by the same reference numerals. FIG. 1 is a schematic circuit diagram showing an embodiment of the differential amplifier circuit of the present invention. The common emitters of the transistors 1.2 forming the differential pair are grounded via a current source 3 which supplies a current T. The input signal Vin of the signal source 4 is applied to the base of these transistors 1.2, and the output current 10Tf is applied to each collector.
r 1 and button stone 2 are output. Furthermore, transistor 2
The collector of is connected to a current feedback circuit 6 through a current mirror circuit 5'f, and the output side of this current feedback circuit 6 is:
Connected to the common emitter of transistor 1.2.

Note that the output current Iotrr from the current mirror circuit 5
3 is drawn out.

Here, assuming that the potential difference between the differential inputs formed at the base of transistor 1.2 is the current drawn from the common emitter, and the common base current amplification factor α of the transistor is 1, the above output current Iotrr 1, l0UT2 is expressed by the following formula.

Next, if the feedback rate of the current feedback circuit is 100%, then By substituting equation (9) into equation (7), the following equation is obtained.

Therefore, the transconductance gm21 of transistor 2
is expressed by the following formula.

By the way, the output current Iotrt3 is the output current l0UT2
Since the force of V is applied to the mirror, Iotrr2 and Ioor3 become equal. Therefore, in the circuit shown in FIG. 1, if the potential difference between the two differential inputs is zero, the current
According to equation (9), it becomes as follows.

xx17v-o ++m2・4 ・・・・・・・・・
(12) By the way, in the conventional circuit shown in FIG. 1, the common emitter current of transistors 1.2 is circular.

Therefore, when the common emitter current of the conventional circuit of FIG. 3 and the embodiment circuit of FIG. 1 are the same, the transfer conductance of transistor 2 in FIG.
From equation 1), this gm22 is expressed by the following equation.

gm21-mu -0-------0(x3)gm2
2-1-IW Therefore, in this embodiment, as is clear from comparing equation (13) with equation (5) (however α-1) described in the conventional example, the transfer conductance of transistor 2 is Compared to the above, the common emitter current can be doubled with the same common emitter current. In other words, this can be achieved with the same transfer conductance 'fc' of the conventional example with a common emitter current of 172, and as a result, a large transfer conductance can be obtained without significantly increasing the power consumption of the circuit.

Therefore, since the amplifier circuit of this embodiment can increase the transfer conductance, it can achieve a large gain for the same load impedance as the conventional amplifier circuit. Furthermore, since the output current can be expressed as an exponential function of the differential input according to equation (10), it can be used as a highly accurate r (gamma) correction circuit.

FIG. 2 is a circuit diagram showing a detailed example of the current mirror circuit 5 and current feedback circuit 6 shown in FIG. 1. The current mirror circuit is a PNP type transistor, and is made up of 9.
A voltage source 10 is applied to the emitter of each transistor, and the base collector of transistor 7 is connected to the base of transistor 8.9. Furthermore, the base and collector of transistor 7 are connected to the collector of transistor 2 forming a differential pair. The older voltage of the voltage source 10 is applied to the collector of the transistor 1 constituting the differential pair. The current feedback circuit 6 is composed of NPN transistors 11 and 12, and the base of the transistor 11 is connected to the base and collector of the transistor 12. The emitter of transistor 11 is grounded and the collector connected to the common emitter of transistors 1.2. The emitter of transistor 12 is grounded, and the base and collector are connected to the collector of transistor 8.

Note that an output current Iotr3 is taken out from the collector of the transistor 9 constituting the current mirror circuit. This output current Iour3 has a transfer conductance expressed by the above equation (13).

Note that the transistor 9 is omitted in FIG. 2, and instead, the base of the NPN transistor 130 shown by the broken line in the figure is connected to the base of the transistor 12, its emitter is grounded, and the output current l0UT3 is taken out from its collector. However, it has the same effect. Note that although the emitter resistors of the transistors 7.8.9 and 11.12 are omitted in FIG. 2, a configuration in which emitter resistors are inserted may be adopted.

〔Effect of the invention〕

As described above, according to the differential amplifier circuit of the present invention, the output current of one of the transistors forming the differential pair is input to the current feedback circuit via the current mirror circuit, and the output of the current feedback circuit is input to the current feedback circuit. By returning the transistors forming the differential pair to a common emitter, a large transfer conductance can be obtained without increasing the power consumption of the circuit.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the differential amplifier circuit of the present invention, Fig. 2 is a circuit diagram showing a detailed example of Fig. 1, and Fig. 3 is an example of a conventional differential amplifier. It is a circuit diagram. 1.2...Transistor 3...Current source 4...Signal source 5...Current mirror circuit 6...Current feedback circuit

Claims (1)

[Claims] A differential amplifier circuit that connects the emitters of a pair of transistors that make up a differential pair to a current source, applies an input signal to the bases of these transistors, and extracts an output current from each collector. a current mirror circuit that supplies the collector current of either one of the pair of transistors; and a current feedback circuit that receives the current of the current mirror circuit and returns the corresponding output current to the common emitter of the pair of transistors. 1.
A differential amplifier circuit characterized in that a current having the same magnitude as a current fed back to a common emitter of a pair of transistors is taken out from the current mirror circuit as an output current.