JPS586408B2 - amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier in which the first stage is a differential amplification stage and a constant current circuit including a Zener diode supplies a constant current to a transistor in a voltage amplification stage. By passing a minute current from the constant current circuit to the transistor of the voltage amplification stage until the voltage reaches the Zener voltage of the Zener diode, it is possible to reliably prevent a shock noise from occurring when the power is turned on. .

Figure 1 shows a conventional amplifier, where 1 is the input terminal of the amplifier, R1 to R3 and C1 are resistors and capacitors that constitute the input circuit, and 2 is transistors Tr1 and Tr.
Tr3 and D1 are transistors and diodes for supplying current to the collectors of transistors Tr1 and Tr2, and Tr4 and R4 are D transistors for drawing current from the emitters of transistors Tr1 and Tr2. and resistors, 3 are transistors Tr5, Tr6, Tr7, resistors R, , R
6. Voltage level shift stage composed of diodes D5tD6, 4 is T? A constant current bias circuit that operates from a low voltage is composed of transistor Tr Tr diodes D2, D3, 829% D4, resistors R7, R8, R, and 5 is an emitter follower for impedance conversion, voltage amplification stage transistor Tr1, and resistor R1. The voltage amplification stage 6 includes a constant current source i and diodes D, D8, and the transistor Tr1 of the voltage amplification stage 5.

7 is a constant current circuit that supplies a current to
1 and R03, 8 is the output terminal of the amplifier, 9 is composed of resistors R14, R15, and capacitor C2, and the output voltage is negatively fed back to the base of the transistor Tr2 of the differential amplification stage. It is a negative feedback circuit.

Note that the constant current source i in FIG. 1 is specifically a transistor Tr constituting a current mirror circuit as shown in FIG.
18, 'rrllll and resistor R18 t R19,
and a Zener diode Ze1 and a resistor R2 (1
It is made up of.

In such a conventional amplifier, the current from the constant current source i does not flow through the voltage amplification stage transistor Tr11 until the power supply voltage +Vc becomes equal to or higher than the Zener voltage of the Zener diode Ze1 after the power is turned on.

Therefore, in the transistors Tr1 and Tr2 of the differential amplification stage 2, the transistor Tr1 is turned on and the transistor Tr2 is turned off due to the difference in the time constant of their respective base potentials.
As a result, the base potential of the transistor Tr5 decreases, and the voltage level shift stage 3 is cut off.

In this way, the differential amplifier stage 2 is completely in the unbalanced region in the time domain in which the loop gain of the amplifier is low and a complete loop is not formed.

In this state, the power supply voltage +Vc is connected to the Zener diode Ze1
When the Zener voltage exceeds , current flows from the constant current source i to the voltage amplification stage transistor Tr11, the differential amplification stage 2 is balanced, the voltage level shift stage also operates, a loop is formed in the amplifier, and the first stage is also stabilized. Become.

However, in this case, the moment the power supply voltage +Vc exceeds the Zener voltage of the Zener diode Ze1, the differential amplifier stage 2 suddenly shifts from an unbalanced state to a balanced state, and the voltage level shift stage 3 also becomes inoperable. The problem is that there is a sudden transition from the state to the operating state (C), a loop is formed in the amplifier, and it enters stable operation, causing a sudden DC fluctuation at the output terminal 8, and at this moment a shock sound is generated from the speaker. .

The present invention provides an amplifier that solves these problems.

An embodiment of the present invention will be described below with reference to FIG.

Components in FIG. 3 with the same symbols as in FIG. 1 have the same functions.

Tr15 is a current supply transistor having a polarity opposite to that of the voltage amplification stage transistor Tr11, and its collector is connected to the collector of the voltage amplification stage transistor Tr11, and its emitter is connected to the power supply +V through a resistor R21.
c, and its base is connected to the output terminal of the constant current bias circuit 4 via a resistor R22.

In other words, the current supply transistor Tr15 is
It is connected in parallel to the constant current source i connected between the power supply ±Vc and the voltage amplification stage transistor Trl1, and is driven by the output of the constant current bias circuit 4.

On the other hand, Tr14 is a muting transistor,
Its base is the voltage level shift stage 3 transistor Tr.
Its emitter is connected to the power supply voltage Vc, and its base is connected to the base of the current supply transistor Trl5.

Furthermore, R23? Collector of transistor Tr5 and power supply +
This is a resistor inserted between Vc.

In the above configuration, when the power is turned on, the constant current bias circuit 4 starts operating at the same time.

The output of the constant current bias circuit 4 drives the current supply transistor Trl5.

Therefore, from the time the power is turned on until the Zener diode Ze1 in the constant current source i operates, a minute current determined by the current supply transistor Tr15 and the resistor R2 flows to the collector of the voltage amplification stage transistor Tr11, and as a result, The loop gain of the amplifier increases and a small loop is formed in the amplifier, and the transistors Tr1 and Tr2 of the differential amplification stage 2
also transitions from a completely unbalanced state to a somewhat balanced state.

After that, when the power supply voltage +Vc exceeds the Zener voltage of the Zener diode Ze1, a current determined by the Zener diode Ze1 flows from the constant current source i, the amplifier has a normal loop gain, the differential amplifier stage 2 is completely balanced, and the voltage The level shift stage 3 enters normal operation, and then the voltage amplification stage 5 operates, and the entire amplifier enters the normal operation state.

At this time, the differential amplification stage 2 shifts from a somewhat balanced state to a completely balanced state, so there is no sudden change as in the conventional case, and therefore no shock noise is generated.

And is the voltage level shift stage 3 operating normally? enter,
When the collector voltage of the transistor Tr5 changes, this change is detected and the muting transistor Tr4 operates, and its collector output is connected to the current supply transistor T.
r15 to turn off this transistor Trl5, and the subsequent voltage amplification stage transistor Tr17
Blocks the supply of minute current to.

In this way, in the above embodiment, when the power is turned on, the power supply voltage +Vc
The loop gain of the amplifier is increased by supplying a minute current to the transistor Trll in the first voltage amplification stage until the voltage reaches the Zener voltage, and a small loop is formed in the amplifier to balance the differential amplification stage 2 to some extent. , when the power supply voltage +■o exceeds the Zener voltage and a constant current is supplied from the constant current circuit 6 to the voltage amplification stage transistor Tr11,
Since the differential amplifier stage 2 is perfectly balanced to give the entire amplifier a normal loop gain, it is possible to reliably prevent shock noise at the moment when the power supply voltage +Vc exceeds the Zener voltage.

Moreover, since this embodiment is configured to detect that the voltage level shift stage 3 has entered normal operation and block the supply of minute current, there is no possibility that the minute current will interfere with the normal operation of the amplifier. Nor.

Note that when such an amplifier is configured with an IC, sufficient current and voltage gains cannot be secured unless a cascode connection is used as the first differential amplifier stage 2 as shown in Figure 4. As a result, there is a problem that the frequency characteristics do not improve.

In this case, as shown in FIG. 4, the transistors Tr16 and Tr17, which are cascode-connected to the transistors Tr1 and Tr2K,
Since the differential amplifier stage 2 is biased at a constant voltage by 1o, it is difficult for the differential amplifier stage 2 to become unbalanced, especially in the time domain where the power supply voltage +Vc is lower than the Zener voltage, and the voltage level shift stage 3 is also turned off more precisely.

Therefore, when the present invention is applied to such an amplifier,
The effect of preventing shock noise when the power is turned on becomes extremely noticeable.

Note that in FIG. 4, i' and ``indicate constant current sources.

As described above, the present invention provides a first differential amplification stage, a voltage level shift stage that level-shifts the output voltage of the differential amplification stage, and a constant current bias that operates from a low voltage to the voltage level shift stage. a constant current bias circuit that supplies a constant current, a voltage amplification stage that amplifies the output voltage of the voltage amplification stage, a constant current circuit that supplies a constant current to the transistor of the voltage amplification stage, and a constant current circuit that amplifies the output of the voltage amplification stage. an output stage, the constant current circuit is connected in parallel with a constant current source including a Zener diode connected between a power source and a transistor of the voltage amplification stage, and the constant current source;
and a current supply transistor driven by the output of the constant current bias circuit, and the current supply transistor is driven by the output of the constant current bias circuit for a period until the power supply voltage exceeds the Zener voltage of the Zener diode when the power is turned on. is turned on, and a minute current is supplied to the transistor in the voltage amplification stage through this current supply transistor, so the loop gain of the amplifier is increased at low voltage immediately after power-on, and a small current is applied to the amplifier. A loop can be formed to balance the differential amplifier stage to some extent, and then when the current voltage exceeds the Zener voltage, the differential amplifier stage can be completely balanced and the whole amplifier can be in a stable operating state. .

Therefore, it is possible to reliably prevent shock noise at the moment when the power supply voltage exceeds the Zener voltage.

Furthermore, if it is possible to detect that the voltage level shift stage is operating normally, turn off the current supply transistor, and prevent the supply of minute current to the voltage amplification stage transistor.
The normal operation of the amplifier is not affected by minute currents.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional amplifier, Fig. 2 is a circuit diagram showing its constant current circuit, Fig. 3 is a circuit diagram showing one embodiment of the present invention, and Fig. 4 is a circuit diagram showing another embodiment of the present invention. FIG. 2 is a circuit diagram illustrating an example differential amplifier stage. 1...Input terminal, 2...Differential amplification stage,
3... Voltage level shift stage, 4... Constant current bias circuit, 5... Voltage amplification stage, 6...
... Constant current circuit, 7 ... Output stage, 8 ...
... Output end, 9... Negative feedback circuit, Tr14.
...muting transistor, Tr15.
... Current supply transistor, Tr16, Tr1
7...Transistor for curse code.

Claims (1)

[Claims] 1. A first differential amplification stage, a voltage level shift stage that level-shifts the output voltage of the differential amplification stage, and a constant current bias that operates from a low voltage and supplies a constant current bias to the voltage level shift stage. a constant current bias circuit that amplifies the output voltage of the voltage amplification stage, a constant current circuit that supplies a constant current to the transistor of the voltage amplification stage, and an output stage that amplifies the output of the voltage amplification stage. and a constant current source including a Zener diode connected between the power supply and the transistor of the voltage amplification stage, and an output of the constant current bias circuit connected in parallel with the constant current source. When the power is turned on, the current supply transistor is turned on by the output of the constant current bias circuit until the power supply voltage exceeds the Zener voltage of the Zener diode, and this current supply is An amplifier configured to supply a minute current to the transistor of the voltage amplification stage through the transistor for the voltage amplification stage. 2. The amplifier according to claim 1, wherein the current supply transistor is turned off by detecting that the voltage level shift stage is operating normally. 3. The amplifier according to claim 1 or 2, which uses a cascode-connected differential amplification stage as the differential amplification stage.