JPS6062713A - Amplifier - Google Patents

Abstract

PURPOSE:To obtain an output with excellent S/N at a small signal input and to obtain an output with excellent distortion factor at a large signal input by activating an amplifier circuit with excellent distortion factor and an amplifier circuit with less noise. CONSTITUTION:When a small signal to which the S/N is important is applied to an input terminal (a), an output signal at a terminal (b) is also small, an output (c) of a rectifier means B is also small, a transistor (TR) Q4 is not operated, TRs Q1, Q3 perform parallel amplification, the amplification factor is large and the S/N is improved. When the input signal is increased, the output (c) of the rectifier means B is increased, the TRQ4 is operated so as to decrease the current flowing to the TRQ2, the gain of the TRQ1 becomes dominant and the distortion factor is improved. Moreover, a gain control circuit comprising TRs Q11, Q8 and Q9 is provided in addition to a gain control circuit comprising the TRs Q2, Q3 and Q4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier, and more particularly to an amplifier whose gain is controlled by an automatic gain control signal.

First, the distortion rate and noise in an amplifier circuit will be explained using FIGS. 1 to 4. Note that FIGS. 3 and 4 are diagrams for explaining the operating points of the circuits shown in FIGS. 1 and 2, respectively.

In Figures 1 and 2, 几, , R, , R, and R4
is the resistance % Q1 and Q are the transistors, RL is the load,
a is a signal input terminal, b is a signal output terminal, 01 and C3 are bypass capacitors, 2 is a constant current source, A is an amplifier in the next stage and subsequent stages, and VCCt is a power supply whose voltage is vcct.

In the circuit shown in Figure 1, the emitter of transistor Q is grounded through resistor R4, so transistor Q
, the pace voltage versus collector current is shown in FIG. 3(a), and its slope is approximately equal to 1/R4. Also, it is given by the pace bias voltage of transistor Q1. If the input signal is a sine wave, the above bias voltage is applied to the center and it is expressed as shown in Figure 3 (a), and the collector current of transistor Q1 in response to that human input signal is as shown in Figure 3 (a).
). The waveform shown by the dotted line in FIG. It is given by equation (2), where Xe<q,> is the transistor Q1
The bias current is expressed in ml. The characteristic of the amplifier shown in FIG. 1 is that by providing a current feedback resistor R4, the nonlinearity of the diode between the base and the base of the transistor can be improved, and as a result, the distortion factor can be improved. Furthermore, it is possible to prevent the base potential of the transistor Q from entering the non-linear region of the VB short. However, by providing the resistor R1Ti', the disadvantage is that the gain decreases as can be seen from the equation (2).
The influence of the noise generated at the output terminal becomes large and the signal-to-noise ratio (signal-to-noise ratio) at the output terminal deteriorates, resulting in an amplifier with an extremely poor S/N ratio.

In Fig. 2, the gain of transistor Q2 is increased to improve the S/C ratio, and a bypass capacitor of 0.0. I have set it up.

Shita force is transistor Q! The base voltage versus output current waveform of FIG. 4 shows a curve as shown in FIG. 4, which approximates the emitter-based diode curve. Figure 4 (a)
is the base input signal waveform of transistor Q, and the third
Figure 4 (Corporate) showing the same sine wave signal as Figure (A) is its collector current waveform.

Figure 2 9 Gain A! is given by the following equation (3).

4- However, Ie(Q,) is the bias current flow of the transistor Q, and the unit is ml. Transistor Q in Figure 2,
In the amplifier configured by , if Ie in equation (3) is chosen large, the gain can be set several tens of times higher than in the circuit shown in Figure 1, which reduces the noise of the amplifier in the next and subsequent stages. It has the advantage of having a small influence and a good S/C ratio. however,
From a distortion point of view, as shown by the dotted line in Figure 4, when the input signal becomes a little large, the distortion of the collector current increases due to the nonlinearity between the base ray and the ray. I can't add it.

By the way, in radio receivers, etc., it is desirable to have a good S/N ratio when the input signal is small, and when the input signal is large, the signal level is large and the S/C ratio is sufficiently large, so it is necessary to use an amplifier that transmits the signal waveform without distortion. is requested.

An object of the present invention is to provide an amplifier that has a good S-R ratio when a small signal is input and an excellent distortion rate when a large signal is input. The object of the present invention is to provide an amplifier with further improved low noise and low distortion characteristics by expanding the gain control function.

The present invention provides a first amplifier circuit with a good distortion factor whose input end is connected to a signal input terminal, a first terminal connected to the output end of the first amplifier circuit, and a signal output terminal connected to the first amplifier circuit. a current supply circuit having a second terminal and in which a current flowing between the first and second terminals is controlled in response to a gain control signal; and a current supply circuit having an input terminal connected to the signal input terminal; a second amplifier circuit with low noise, the output terminal of which is connected to the first terminal or the second terminal; and a second amplifier circuit that controls the operating current of the second amplifier circuit in response to the gain control signal. The invention is characterized by comprising means for controlling gain.

In this manner, the present invention obtains an output with an excellent distortion rate when the first amplifier circuit with a good distortion rate and the second amplifier circuit with a low noise are inputted. moreover,
A current supply circuit whose current supply capability is controlled in response to a gain control signal is provided between at least the output terminal of the first amplifier circuit and the signal output terminal to expand the gain control range and further improve noise and distortion characteristics. are improving.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 5 shows an embodiment of the present invention, which includes resistors R1 to '', transistors Q to Q, capacitors 01 and 01, load voltage, power supply VCC%, and other amplifier A.
1 and a rectifier circuit (automatic gain control signal generation circuit) B.

Next, its operation will be explained. When the input signal is relatively small, the output signal applied to the terminal is also small, and as a result, the rectified output at the terminal C produced by the rectifying means B is small. Therefore, the transistor Q4 is in a non-operating state. 0 In other words, equation (3) becomes as follows.

A 6 = A 1 + A 2 Since it is expressed as the sum of the amplification degree of the circuit in Fig. 1 and the amplification degree of the circuit in Fig. 2, the amplification degree is sufficiently higher than that in Fig. The influence of noise generated in the S/N is small.
The ratio can be increased.

When the input signal increases, the rectified output of rectifying means B increases, the voltage at terminal 0 rises, and transistor Q4 operates,
The base potential of transistor Q3 is lowered, and transistor Q
, to reduce the current flowing through the . Therefore, the denominator of the second term A in equation (4) becomes large, and the p gain A0 decreases. A gain control circuit is constituted by the rectifying means A, the transistors Qt +Q, and Q4, and due to the function of this gain control circuit, As the input signal increases, the amplification degree of the transistor Q is reduced, and the gain of the transistor Qt becomes dominant. As a result, the influence of distortion caused by transistor Q2 on the output signal can be reduced. For even larger input signals, the transistor Q is cut off and no longer transmits multiple signals, and the distortion caused by the transistor Q no longer occurs in the output.

In this way, it has the characteristics of a large S-to-low input signal ratio and little distortion for large input signal levels, but since the next stage amplifier A further amplifies the signal, distortion is more likely to occur. A large amount of gain control is desired for the first stage amplifier, and to meet this requirement, transistor Q.

In addition to the gain control circuit formed by Qs=Q, a gain control circuit of transistors Qsi + Qtr + Qo is further provided. That is, when the input signal level is sufficiently low and the rectified output voltage at terminal 0 is small, the gain control transistor Q4 and the transistor Q.

When in a suspended state, transistors Q,,Q,. In the interrupt state, transistors Q, , Q, are in the active state. That is, the base potential of the transistor Q is higher than the base potential of the transistor Q by the potential drop of the diode DI, and the base potential of the transistor Q is higher than the base potential of the transistor Q. This is because they are each set higher than the base potential of R1 by the potential drop of R1. Therefore, transistor Q1 and transistor Q! operates as a parallel amplifier and is cascaded with transistor Q to transmit the signal current to the load. As the input signal increases, the rectified output at terminal C increases, and transistor Q4 and transistor Q
11 becomes operational, each transistor Q
, and lower the base potentials of Q. As the input signal increases, the base potential of transistor Q3 gradually approaches the base potential of transistor Q+o, and the base potential of transistor Q9 approaches the base potential of transistor Qs, so that the currents of transistor Q and transistor Q decrease. As a result, the gain of transistor Q decreases. The decrease in the current of transistor Q9 is due to the decrease in the current of transistor Q9.
1 and transistor 10, the base potential of transistor Q is
1°, the base potential of transistor Qll becomes lower than that of transistor Qs, and transistors Q and Q
At 9, the current becomes extremely low.

At this time, the value of R1 is set so that the voltage drop across resistor R1 is smaller than the voltage drop across diode D, so the current in transistor Q is made to decrease faster than transistor Q0. I can do it. Furthermore, the resistance R
, ,R, ,R, , ,R1, are selected so that the values have the following relationship, so the effect is remarkable! 0% By choosing the value on the right side of equation (5) to be sufficiently larger than the value on the left side, the current in transistor Q decreases.

Therefore, it is possible to realize a first stage amplification having a gain control circuit with extremely small distortion even when the input signal level fluctuates widely. Note that the diode D□D4 prevents the transistor Q4 from becoming saturated.

In FIG. 5, the collector of transistor Q is connected to the collector of transistor Q, but these are disconnected and the collector of transistor Q is connected to the collector of transistor Q! Even if the collector is connected, the same operation and effect as the circuit operation shown in FIG. 5 can be obtained.

Also, in semiconductor integrated circuits, transistor Q.

It is clear that the transistors Q*'ti and Q*'ti - multi-A with the same collector and the same base can have a similar structure and the operation will be exactly the same in this case as well.

As described above, according to the circuit configuration according to the present invention, it is possible to perform large gain control without impairing the S/N ratio even at a small input signal level, and it is an amplifier with extremely low distortion even at a large input signal, and has low noise. Furthermore, an amplifier with further improved low distortion is provided.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams for explaining the distortion factor and noise characteristics of the amplifier, and Figures 3 and 4 are circuit diagrams for explaining the operation of the circuits in Figures 1 and 2, respectively. figure,
FIG. 5 is a circuit diagram showing an embodiment of the present invention. R,, R,,..., R1, are resistances, Dl,..., D
4 is the diode% Ql + Ql +..., Qo,
is a transistor, 0. . 0, H is a bypass capacitor, ZD is a Zener diode,
VCC, is a power supply, engineering is a constant current source, a, b, and C are terminals, RL is a load, person is an amplifier in the next stage and subsequent stages, and B is a rectifier. 13- Me Z diagram Figure 4

Claims (1)

[Claims] A first amplifier circuit with a good distortion factor whose input terminal is connected to the signal input terminal, a first terminal connected to the output terminal of this first amplifier circuit, and a second terminal connected to the signal output terminal. a first gain control circuit having an input terminal connected to the signal input terminal, the impedance between the first and second terminals being controlled in response to a gain control signal; and the first gain control circuit having an input terminal connected to the signal input terminal. a second amplifier circuit having an output terminal connected to the first terminal or the second terminal of the amplifier circuit and having less noise; and a second amplifier circuit that controls the operating current of the second amplifier circuit in response to the gain control signal. An amplifier characterized by comprising a gain control circuit.