JPS5840370B2 - Zoufuku Cairo - Google Patents

Description

[Detailed description of the invention] The present invention relates to a direct coupled multi-stage amplitude limiting amplifier circuit.

When a direct-coupled multistage amplifier circuit is used for FM intermediate frequency amplification, one of the input waveforms may be underdriven when a large signal is input, resulting in an output waveform that lacks symmetry.

First, the cause of this will be explained using a conventional circuit example.

FIG. 1 is a diagram showing a conventional example of an amplitude limiting amplifier circuit.

This circuit operates as follows. An input signal applied from the input terminal 17 to the base of the amplifying transistor 10 is taken out from the collector of the transistor 2 whose emitter is coupled to the transistor 1.

This signal is then applied to the base of emitter follower transistor 30, from the emitter via resistor 22 to the base of transistor 50, and taken out from the collector of transistor 6 which is emitter-coupled with transistor 5.

The bias circuit connects resistor 2 from the emitter of transistor 3.
Bias is supplied to the transistors 1 and 2 and the base of the transistor 60 through the transistor 3.

In such a gain control circuit, the resistor 22 cannot have a large resistance value because of the loss of gain, and similarly, the resistor 23 is usually selected to have a resistance of several hundred ohms.

Therefore, the AC impedance at the emitter of the emitter-follower transistor is several hundred ohms at most, and when a large signal is input, the lower side of the signal waveform at the emitter of transistor 3 is underdriven, resulting in an output waveform with no symmetry. It happens.

Furthermore, as is well known, when the bias resistors 22 and 23 are made of diffused resistors in a semiconductor integrated circuit, there is a manufacturing limit to increase the absolute accuracy of the resistance value, and the variation in the resistance value is This causes a potential difference between the voltages and the voltage, which causes the amplitude limiting effect to deteriorate.

The purpose of the present invention is to obtain an output waveform that does not lose its symmetry even when the power supply voltage changes, and to obtain a sufficient amplitude limiting effect with a small number of external terminals, which is advantageous for semiconductor integrated circuits. The object of the present invention is to provide a limiting amplification circuit.

In order to achieve the above object distantly, an amplifier circuit according to the present invention is provided.
, a first differential amplifier including a second transistor, and a second differential amplifier including third and fourth transistors directly connected to the first amplifier via an emitter follower amplifier. In the amplifier, the third and fourth
a fifth transistor, each having its base connected to a transistor of
The sixth transistor is connected in a differential manner, and the base of the seventh transistor is connected to the collector of the sixth transistor, and negative feedback is provided to the base of the sixth transistor through the emitter circuit using only a DC component. , and is further configured to apply a base bias to the first and second transistors using the DC component of the emitter circuit of the seventh transistor.

According to the above configuration, the above-mentioned drawbacks are completely eliminated and the object of the present invention is achieved.

The present invention will be explained in more detail below with reference to FIG. 2 showing an embodiment according to the present invention.

In the circuit according to the present invention, the base of the transistor 40 is connected to the base of the transistor 50, and the base of the transistor 7 is connected to the base of the transistor 60.
The collector of transistor 7 is connected to the base of emitter follower transistor 80, with the collector of transistor 7 and the emitter of emitter follower transistor 80 connected as a load, and the emitter of transistor 7 is connected to the base of emitter follower transistor 80.
6, it is configured to have low AC impedance and to be supplied as a bias to the bases of transistors 1, 2, and transistor 70.

The other configurations are the same as the circuit shown in FIG. 1 described above.

First, when the power supply voltage fluctuates, the transistor 1°2.4
, 5, 6, and 7 will be explained.

It is connected from the collector of transistor 2 through emitter follower transistor 3 to the base of transistor 4, and from the collector of transistor 7 through emitter follower transistor 8 to the base of transistors 1, 2, 6, and 70.
It constitutes a DC closed bias circuit.

Therefore, fluctuations in the base voltages of transistors 1 and 20 are compressed by the closed circuit gain, and for example, the closed circuit gain is 10
If it is 0 times, it becomes 1/101, which is 0.99% of the variation in the base voltage of transistors 1 and 2.
It will be about.

That is, by adding the transistors 4, 7, and 8, the closed circuit gain becomes higher, and the bias fluctuation is reduced accordingly.

Next, consider the emitter impedance of the emitter follower transistor 3.

As can be seen from FIG. 2, the AC impedance at the emitter is a composite value of the emitter resistance 12 of the emitter follower, the input impedance of the transistor 4, and the input impedance of the transistor 5.

Compared to the conventional example, since the impedance is sufficiently high, there is less possibility that the symmetry of the output signal waveform will be lost even when a large signal is input, and an improvement in the AM suppression ratio can be expected.

As explained above, the amplitude limiting circuit according to the present invention is
Even when the power supply voltage fluctuates, there is little bias fluctuation.
Moreover, it becomes possible to amplify the output waveform without loss of symmetry.

Furthermore, since it is suitable for semiconductor integrated circuits, it can be said that the practical effects are extremely large.

Various modifications can be made to the embodiments described in detail above within the scope of the claims.

In short, the scope of the present invention extends to all of the claims.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram for explaining the configuration of a conventional circuit;
The figure is a circuit diagram showing an embodiment of an amplifier circuit according to the present invention. 1.2, 4, 5, 6, 7...Transistor for differential amplification, 3...Transistor for emitter follower, 8...Emitter follower transistor for bias supply, 9 , 15...Load resistance, 17...
...Signal input terminal.

Claims (1)

[Claims] 1 first and second transistors connected in a differential manner, a third transistor whose base is connected to the base of the first transistor, and a third transistor whose base is connected to the base of the second transistor. 4 transistor, means for differentially connecting said third and fourth transistors, means for guiding an input signal to both said first and third transistors, and means for connecting said third and fourth transistors in a differential manner; An amplifier circuit comprising: a DC negative feedback circuit provided at the base of the third transistor; and means for obtaining an output from at least one of the first and second transistors.