JPH02285704A - Variable gain differential amplifier circuit - Google Patents

Abstract

PURPOSE:To operate the circuit with a low power supply voltage by constituting an emitter constant current bias source for a 1st and a 2nd differential amplifier circuit with a common emitter circuit and driving each base with a 3rd differential amplifier circuit whose input terminal receives a gain control voltage. CONSTITUTION:With a control voltage applied between terminals 5, 6, a ratio of collector currents of transistors(TRs) 21, 22 is changed. TRs 16, 18, resistors 37, 41 and TRs 16, 17, resistors 38, 40 constitute respectively a current mirror circuit, and a collector power supply comprising the TRs 21, 26 and TRs 22, 15 has a prescribed ratio depending on the ratio of the resistors 38, 40 and the resistors 37, 41 respectively. Thus, the resistance of the resistors 37, 38 and the resistors 40, 41 is selected respectively the same to make the sum of collector currents of the TRs 15, 16 to be a constant value having a prescribed ratio to the current of the constant current source 9. Collectors of the TRs 15, 16 are connected to two sets of differential TRs 11, 12 and 13, 14 connecting to same load resistors 31, 32 via emitter resistors 33-36, the control voltages 5, 6 are varied to vary the gain of the amplifier circuit comprising the TRs 11-14 and the resistors 31-36.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplifier circuit capable of gain control, and particularly to a variable gain differential amplifier circuit suitable for integrated circuits and capable of low voltage operation.

[Conventional technology] FIG. 5 shows an example of a conventional current summation n-type differential amplifier circuit.

In FIG. 5, each collector current of a differential amplifier circuit composed of transistors 15 and 16 is controlled by gain control signals applied to input terminals 5 and 6. transistor 1
9 operates as a constant current circuit used in the differential amplifier circuit. The collector currents of the 1-run listers 15 and 16 are input to the emitters of transistors 11 and 12 and 13 and 14, which constitute two differential circuits, through resistors 33 to 36, respectively. The bases of the transistors 11 and 14 and 12 and 13 are commonly connected to each other, and an input signal voltage is applied between them. Further, the collectors of the transistors 11 and 13, and the collectors of the transistors 12 and 14 are also connected in common, and the signal voltage at the end of the resistor 31 or 32 is taken out as an output voltage from the terminal 3 or 4. Since the magnitude of this output voltage can be controlled by the above-mentioned control voltage, this circuit operates as a differential amplifier circuit with variable gain.

[Problems to be Solved by the Invention] In the conventional circuit explained using FIG. 5, it is necessary to connect two differential circuits, their respective emitter resistors, collector resistors, etc. in series between the power supply terminal 8 and the ground potential. top, at least 3
(2) It requires a power supply voltage higher than 1, and furthermore, there is a problem that the maximum output voltage that can be obtained is low even though a relatively high power supply voltage is used.

In particular, recent integrated circuits are becoming increasingly finer and their withstand voltages are decreasing, and there is a demand for circuit configurations that can obtain a large output voltage with a low power supply voltage and high gain at the same time. is inconvenient.

SUMMARY OF THE INVENTION An object of the present invention is to provide a variable gain differential amplifier circuit that eliminates the drawbacks of the conventional circuit and provides a large output voltage and high gain with a low power supply voltage.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for each of a pair of base input terminals of a first differential amplifier circuit and a pair of base input terminals of a second differential amplifier circuit. are connected in common and an input signal is applied to the collector, which outputs an output signal in phase with the input signal of the first differential amplifier circuit, and an output signal of the opposite phase of the second differential amplifier circuit. The collectors are connected in common, and similarly, the collector that outputs the opposite phase output signal of the first differential amplifier circuit and the collector that outputs the in-phase output signal of the second differential amplifier circuit are connected in common. In the current addition type differential amplifier circuit, each of the emitter constant current bias sources of the first and second differential amplifier circuits is configured with an emitter grounded circuit, and the base of each of the two emitter grounded circuits is connected to a diode. A series connection circuit of resistive elements is used as a collector load,
It is driven by a third differential amplifier circuit to which a gain control voltage is applied to its input terminal.

[Operation] The variable gain differential amplifier circuit configured as described above can reduce the number of transistors inserted between the power supply and the ground potential by one, and therefore operates at a lower power supply voltage than the conventional circuit.

[Example] Hereinafter, the configuration of an example of the present invention will be described using FIGS. 1 to 4. In FIG. 1, a diode-connected transistor 17.18 and a resistor 39.4 are connected to the collectors of a PNP transistor pair 21.22 operated by a constant current source 9.
0 series connected circuits are each connected as a load. By applying a control m+rFi pressure across terminals 5.6, the ratio of the rector current values of transistor 21.22 can be varied. Transistor 15.18, resistor 37°41, transistor 16.17, and resistor 38.40 constitute a current mirror circuit, and transistor 2
The collector currents of transistor 1 and transistor 16 and transistor 22 and transistor 15 have a constant ratio determined by the ratio of resistor 38 to resistor 40 and resistor 37 to resistor 41, respectively. Therefore, by making the resistance values of the resistors 37.38 and 40.41 the same, the transistor 15.1
The sum of the collector currents 6 and 6 can be set to a constant value having a constant ratio to the current value of the constant current source 9. The collectors of the transistors 15.16 are then connected to the respective emitter resistors 33 to two differential transistor pairs 11.12 and 13.14, the respective collectors of which are connected to the same load resistor 31.32.
~36, and by changing the control 11m pressure 5.6, the 'Fi current ratio flowing through the resistors 31 and 32 can be changed while keeping the sum of the differential currents of these two transistor pairs constant. can be done. As a result, transistor 11
14, the gain of the amplifier circuit constituted by the resistors 31 to 36 can be made variable.

Comparing the circuit according to the embodiment of the present invention shown in FIG. 1 and the conventional circuit shown in FIG. 5, in the case of FIG. 5 three transistors are inserted in series between the power supply terminal 8 and the ground point. on the other hand,
In the case of Fig. 1, it can be seen that two pieces are inserted in series. Therefore, the present invention has the advantage that the power supply voltage can be set low because the number of transistors is small.

The above-mentioned advantages can be similarly applied to other embodiments of the present invention described below with reference to FIGS. 2 to 4.

FIG. 2 shows another embodiment of the present invention constructed by transistors 23 to 25, resistors 42 to 44, and current setting voltage 7. Transistor 23 supplies the current of the constant current source, and a series circuit including transistors 24 and 25 and resistors 42 and 44 generates a bias voltage to be applied to the base of transistor 23.

FIG. 3 shows another embodiment of the present invention in which the pair of pace terminals of transistors 11 to 14 of FIG. 1 are separated and independent input signals are applied to each pair. By inputting two signals to the input terminals 1, 2, 51 and 52 as a pair, it can be used for switching between two signals, analog addition/subtraction calculations, etc. At this time, the emitter resistances 33 to 3 of the differential transistor pair
6 may all have the same value.

Figure 4 shows transistors 15 to 18 in Figures 1 to 3.
Another embodiment of the present invention in which transistors 26, 27 are added to the current mirror circuit portion constituted by resistors 37, 38, 40, 41, etc., and each of them is made into a 3-transistor type current mirror circuit to increase the mirror coefficient. This is an example circuit. This is particularly effective when the current amplification factor hFE of the transistors 15 to 18 is relatively small or when controlling a plurality of current source circuits.

[Effect of the invention 1 As detailed above, when the present invention is applied, the number of transistors inserted between the power supply and the ground potential in the conventional current addition type variable gain differential amplifier circuit can be reduced by one. Therefore, it is possible to provide a current addition type variable gain differential amplifier circuit in which the power supply voltage is lowered by about 1V.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a current addition type variable gain differential amplifier circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific configuration example of the embodiment of the present invention, FIGS. This figure shows the configuration of another embodiment of the present invention, and FIG. 5 is a diagram showing an example of the configuration of a conventional Ti current addition type variable gain differential amplifier circuit. 1, 2. 51. 52 3.4 5.6 11~18.25~27 21~24 31~38: Differential signal input terminal, : Differential signal output terminal, : Gain control signal input terminal, : Reference voltage input terminal for constant current source , positive Ti source terminal, constant current source circuit, NPN transistor, PNP transistor, resistor. Children's country light shield

Claims (1)

[Claims] 1. A pair of base input terminals of the first differential amplifier circuit and a pair of base input terminals of the second differential amplifier circuit are each connected in common and an input signal is applied to the first differential amplifier. A collector that outputs an output signal in phase with the input signal of the circuit and a collector that outputs an output signal of the opposite phase of the second differential amplifier circuit are connected in common, and similarly, a collector that outputs an output signal in phase with the input signal of the circuit is connected in common, In the current addition type differential amplifier circuit in which a collector that outputs a phase output signal and a collector that outputs an in-phase output signal of the second differential amplifier circuit are connected in common, the first and second differential amplifiers Each of the emitter constant current bias sources of the circuit is configured with a grounded emitter circuit, a series-connected circuit of diode resistance elements for driving the bases of each of the two grounded emitter circuits is used as the collector load, and a gain is connected to the input terminal of the circuit. A variable gain amplifier circuit comprising a third differential amplifier circuit that applies a control voltage.