JPS58195309A - Voltage gain controlling amplifier - Google Patents

Abstract

PURPOSE:To reduce noise generated due to a DC current with a simple constitution, by connecting a common emitter of a couple of transistors (TR) to a constant current source so as to flow a constant current to the common emitter and reducing the DC current flowing to the couple of TRs by the amount in response to the constant current. CONSTITUTION:When a sinusoidal input signal voltage of a maximum amplitude is impressed to an input terminal IN, since a current IO flows to the common emitter of the TRs Q1, Q2 from the constant current source IO, a collector current as shown in figure flows to the TRQ2. Although a DC current more than the required minimum current flows to an amplifier of conventional systems superimposingly, the amplifier of this invention calls for the required minimum DC current. Then, noise due to current is lower in the amplifier of this invention in comparison with the conventional system. Further, the amplitude of the constant current from the constant current source IO should be set to a value so that a current in response to the input signal voltage of the maximum amplitude can be given to the TRQ2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage gain controlled amplifier whose gain is controlled by voltage.

Conventionally, such an amplifier includes a pair of transistors Q1 and Q2 of the same conductivity type whose emitters are interconnected to form a differential amplifier, as shown in FIG. A constant voltage ■c is given to The output signal corresponding to the amplified input signal is connected to the collector of the transistor Q2 and the resistor R.
There is something that is obtained from the connection point with 2.
.

Further, the input circuit of this amplifier is provided with a voltage-current conversion circuit composed of transistors Q4 to Q6 including transistor Q3. This consists of constant current source ■, differential pair transistors Q4 and Q5, and current mirror Q6*Q?
It consists of a differential amplifier and other active loads.

However, the voltage-current 1f as the input circuit described above
Due to the limitations of the E-conversion circuit, a bias current larger than that required by the voltage gain control amplifier flows through the transistor Q3, which has the drawback of increasing the noise component.

The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to provide a voltage gain control amplifier that reduces noise by preventing more current than necessary from flowing through the transistors. be.

The present invention will be explained below with reference to FIG. 2 and subsequent figures.

As shown in FIG. 2, the voltage gain control amplifier according to the present invention has a constant current source io connected to the common emitters of transistors Ql and C2 so that a constant current flows into the common emitter. It has the same configuration as the circuit.

If a constant current flows through transistor Q3 and the base voltages of transistors Q1 and C2 are equal, then the first
In the circuit shown in the figure, both transistors Q1 and C2 each have 1/
A current of 21 + flows.

On the other hand, in the circuit of FIG. 2, if the current flowing into the common emitter by the constant current Io is Io, then the transistor Ql-
A current of 1+, io>/2 flows through Q2, which decreases compared to the case shown in FIG. Assuming that a sinusoidal input signal voltage is applied, a collector current as shown in FIG. 3(a) flows through transistor Q2 in the conventional amplifier of FIG. Now, since the constant current source 1o causes the current 1o as shown in FIG. 3 (bl) to flow into the common emitter of the transistors Q+ and C2,
A collector current as shown in will now flow. As can be seen by comparing the collector currents of ia+ and peaks in Figure 3, in the conventional amplifier, a DC current exceeding the necessary amount flows in a superimposed manner, whereas in the amplifier according to the present invention, the minimum necessary DC current flows. only are superimposed. Therefore, in the amplifier of the present invention, noise caused by current is reduced compared to conventional amplifiers.

Note that the thickness of the constant current that the constant current H1o flows into is such that the current corresponding to the input signal voltage of the maximum amplitude is passed through the transistor Q2.
It must be set to a value that allows it to flow. 11 In addition, although a voltage-to-current conversion circuit consisting of a differential amplifier is used as an input circuit, other voltage-to-current conversion circuits may be used.1 As described above, the present invention
Since a constant current source is connected to the common emitters of the pair of transistors forming the same structure, and a constant current is allowed to flow into the common emitters, the direct current flowing through the pair of transistors decreases in response to this constant current. As a result, an extremely excellent effect can be obtained in that noise generated due to direct current can be reduced with a simple configuration.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a conventional voltage gain control amplifier.
FIG. 2 is a circuit diagram showing an embodiment of the pressure gain control amplifier according to the present invention, and FIG. 3 is a graph for explaining the difference in operation between the conventional example and the amplifier according to the present invention. Q+, C2, C3...transistor, Io...
Constant current source. Patent applicant Pioneer Corporation

Claims (1)

[Claims] A current source that flows a signal current that varies depending on the input signal voltage is connected to the common emitters of a pair of differential transistors of the same conductivity type, and a constant current source that flows a constant current is connected to the common emitters. A voltage gain control amplifier whose gain is controlled by the voltage applied between the bases of the transistors.