JPS6010106Y2 - cascade amplifier - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a cascade amplifier.

Conventionally, this type of amplifier has had a problem in that it lacks stability because the collector current of the amplifier circuit fluctuates due to changes in bias voltage.

The purpose of the present invention is to improve the above-mentioned drawbacks of the conventional technology, and to eliminate fluctuations in collector current and have stable characteristics by connecting a series stabilizing circuit to the bias circuit of the final stage amplifier circuit of a cascade amplifier. To provide a cascade amplifier.

Another object of the present invention is to provide a cascade amplifier that can supply stable power to other stage circuits by omitting bias resistors in stages other than the final stage amplifier circuit and reducing power consumption. There is something to do.

The cascade amplifier of the present invention uses a transistor and a constant voltage diode (Zener diode) in the bias circuit of the transistor in the final stage amplifier circuit. The present invention is characterized in that a series stabilizing circuit is connected which acts to lower the voltage and suppress fluctuations in the emitter voltage.

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

FIG. 1A shows an example of a conventional cascade amplifier in which feedback is provided from the rear stage to the front stage, and FIG. 1A shows an example in which feedback is performed separately for each stage.

First, to explain the conventional example shown in FIG. 1, C1 and C2 are coupling capacitors, C2, C3 and C3 are decoupling capacitors, T1. T2. T3 is a matching transformer, and all of these act for high frequency amplification and are not directly related to the bias circuit of the present invention, so their explanation will be omitted.

, R□, R2, and R3 are bias resistors that determine the collector current of transistor Q1, and R4 and R5 are bias resistors that determine the collector current of transistor Q1.
This is a bias resistor that determines the collector voltage of 2.

In the example of Figure 1a, the base voltage of transistor Q2 is
8□ is ■ if the power supply voltage is VCC.

. ×4 ゜, +.

It is determined by the ratio of R4 and R5 as shown in . Since the collector voltage ■c1 of the transistor Q□ is the same as the emitter voltage ■E2 of the transistor Q2, that is, VBE2 is the base-emitter voltage of Q2 and is sufficiently small.

On the other hand, transistor Q1. The collector NFE of Q2 is It is expressed as

Therefore, in FIG. 1a, V from equation (2).

■ for a change of 0. Therefore, in the circuit of FIG. 1, the change in I with respect to the change in VCC.

The change in equation (3) disappears, but IC changes.

As described above, in the conventional cascade amplifier, the collector current of each stage fluctuates due to a change in bias voltage, so the gain and distortion level of the amplifier change and become unstable.

In addition, the collector current changes due to changes in the power supply voltage caused by ripples, resulting in various drawbacks such as hum modulation.

FIG. 2 shows a circuit diagram of a cascade amplifier according to the present invention. The same reference numerals are used for the same components as in the conventional example shown in FIGS. 1a and 1b, and the explanation thereof will be omitted.

The difference from the conventional example is that a series stabilizing circuit constituted by a transistor Q3, a Zener diode (constant voltage diode) Dl, and bias resistors R6 and R6 is connected as a bias circuit to the final stage amplifier circuit.

That is, in the present invention, the transistor Q of the final stage amplifier circuit
A transistor Q3 and a Zener diode D1 are inserted in series in the base circuit of No. 2, and the base of this transistor Q3 is connected to the collector resistor R4 of the transistor Q□ in the previous stage to which the transistor Q2 is cascade-connected, and between it and ground. Connect the bias resistor island.

According to the cascade amplifier of the present invention, when the emitter voltage VE2 of the transistor Q2 increases, the base voltage VB3 of the transistor Q3 increases.

The emitter voltage of transistor Q is constant due to the action of Zener diode D1.

Therefore, the base-emitter voltage VBE of transistor Q
3 rises, the collector current of the transistor Q3 flows, the voltage drop across the bias resistor R5 becomes large, and the base voltage of the transistor Q2 is lowered by 8 degrees.

Therefore, the emitter voltage VE2 of the transistor Q2 becomes constant.

Note that R7 is a resistor for flowing current to the Zener diode D□.

That is, where V o 1 is the voltage across the Zener diode D.

Therefore, transistor Q1. Therefore, it can be seen that h of the collector current IC of Q2 does not change due to changes in the bias voltage and thus the power supply voltage Vcc.

Furthermore, since the collector voltage of transistor Q does not change, its bias circuit is simpler than the conventional one.

That is, the resistor R1 can be omitted. ■ In this case. is the following (6
) does not change depending on the bias voltage, as shown in the equation.

Here, β is the current amplification factor of the transistor Q0, that is, the base current of Q□ is ib, and the collector current is ic.Although the above embodiment is applied to a high frequency amplifier, it can be similarly applied to other amplifiers. Of course it can be done.

As described above, according to the bias circuit of the present invention, (1) there is no change in the gain or distortion level of the cascade amplifier, and an amplifier with stable characteristics can be obtained.

■ Hum modulation is reduced because the collector current of each stage amplifier circuit does not change due to the change in power supply voltage due to ripple.

■ Current consumption can be reduced because the bias resistor of each amplification stage other than the final stage can be omitted.

(2) By making the collector current of the final stage amplifier circuit larger than that of the price, it is possible to supply a current corresponding to the difference between the two currents from the final stage emitter circuit as a power source for other circuits.

It has the following effects.

[Brief explanation of the drawing]

1A and 1B are circuit diagrams of a conventional cascade amplifier, and FIG. 2 is a circuit diagram of a cascade amplifier according to the present invention. C1, C4...Coupling capacitor, C2
゜C3, C5...decoupling capacitor,
Ql. Q2. Q3...Transistor, VCC...
...Power supply voltage, Dl... Constant voltage diode, T
1. T2. T3... Matching transformer.

Claims (1)

[Scope of utility model registration request] In a cascade amplifier circuit having a plurality of amplifier stages, the collector of a bias transistor is connected to the base of the transistor of the final stage amplifier circuit, and a constant voltage diode is connected between the emitter of this bias transistor and the ground, A cascade amplifier, wherein the base voltage of the transistor is obtained from the emitter voltage of the transistor of the final stage amplifier circuit, and the collector and emitter of the bias transistor are respectively connected to the power supply of the cascade amplifier circuit via a resistor.