JPS58202613A - Differential amplifying circuit - Google Patents

Abstract

PURPOSE:To improve the high frequency characteristics of a differential amplifying circuit, by using two base-earthed amplifying circuits consisting of a transistor TR and a load resistance respectively. CONSTITUTION:Two base-earthed amplifying circuits are formed with TR1 and TR2 and load resistances 5 and 6 respectively. The base terminals of these two amplifying circuits are used in common with each other, and the current flowing through the common base terminal is set at a constant level. Therefore the sum is constant for the collector currents of the TR1 and TR2. Thus it is possible to amplify the difference between input voltages applied to input terminals 3 and 4. This increases the band width with high gain for a differential amplifying circuit. This circuit contains a constant current circuit A' and plus and minus power supply terminals B and C respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high gain, particularly wide bandwidth, differential amplifier circuit in a grounded-to-ground configuration.

A conventional differential amplifier circuit uses two common emitter amplifier circuits as shown in Figure 1, and connects the common emitter terminal to a constant current circuit A to keep the current flowing through the common emitter terminal constant.
The operation was such that the sum of the collector currents of transistors 1 and 2 was kept constant, and the difference between the input voltages applied to input terminals 3 and 4 was amplified. However, due to the common emitter configuration, the high frequency characteristics of the transistors used are limited by the β-cutoff wave number fβ, and the differential amplifier circuit with this configuration has the disadvantage of a narrow bandwidth.

In order to eliminate such drawbacks of the conventional differential amplifier circuit, the present invention is characterized in that the high frequency characteristics of the differential amplifier circuit are improved by using a common base configuration.

Details will be explained below using the drawings. Since the high frequency characteristic of the common base amplifier circuit is dominated by the α-cutting simple wave number fα, the bandwidth is wider than that of the common-emitter amplifier circuit in which the β-cutting simple wave number fβ is dominant.

If this is applied to a differential amplifier circuit, a differential amplifier circuit with high gain and wide bandwidth can be created.

FIG. 2 is a basic circuit of the present invention. If the base terminals of the two base-grounded amplifier circuits are made common and the current flowing through the common base terminal is kept constant, the sum of the collector currents of transistor 1 and transistor 2 will be constant, and input terminal 3,
It is possible to amplify the difference between the input voltages applied to each of the four input voltages, resulting in a wide-bandwidth, high-gain differential amplifier circuit.

FIG. 3 shows an embodiment of the present invention in which two common base amplifier circuits each consisting of a transistor and a load resistor 5, and a transistor 2 and a load resistor 6 have a common base terminal, and the common base terminal is connected to an FE' It is connected to a minute constant current circuit A' composed of l'9 and transistor 0. Since the base is common, the current flowing through the common terminal is minute, and the first
The optical circuit A cannot use the conventional settings as shown in the figure. Therefore, as shown in A' in FIG. 3, a transistor 10 is connected to the FET 9 to form a minute constant current circuit.

A constant current circuit consisting of FET9, transistor 10
The collector current of the transistor 1 is constant, and the base current is the collector current divided by the current amplification degree.
00 base current becomes constant, and the common base terminal current can be kept constant.

In addition, in Figure 3, an emitter follower circuit is connected before the common base circuit, and the input input logic of the circuit is established.

Prevents dance from deteriorating.

With the above circuit configuration, it is possible to realize a differential amplifier circuit with a common base configuration and widen the bandwidth of the differential amplifier circuit.

[Brief explanation of the drawing]

FIG. 1 shows a conventional differential amplifier circuit, FIG. 2 shows a basic circuit according to the present invention, and FIG. 3 shows a circuit according to an embodiment of the present invention. In the figure, 1, 2... differential amplification transistor, 3, 4... input terminal, 5, 6...
...Load resistance, 7, 8...Emitter follower transistor, 9...PET for constant current, 10.
・・Transistor for large current/small current conversion, A, A
'... Constant current circuit, B, C... Power terminals (positive, negative). Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A differential amplifier circuit characterized by a configuration in which two base-grounded amplifier circuits have a common base terminal, and the common pace terminal is connected to a minute constant current circuit.