JPS5951165B2 - power amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a two-stage directly connected differential amplifier composed of two sets of differential pair transistors of opposite conductivity types, and a bush-pull output amplifier driven by the output of the differential amplifier. The present invention relates to a power amplifier, and particularly to a power amplifier that prevents the generation of pop sounds when the power is turned on.

The preamplifier stage that makes up the power amplifier settles to a predetermined bias condition after a certain period of time after the operating power is turned on to the power amplifier. The bias conditions of the pair of amplifying elements constituting the bush-pull output amplifying stage become unbalanced with each other, resulting in the generation of pop sounds that are undesirable to the ear.

It is an object of the present invention to prevent the generation of pop noise in a power amplifier, particularly when a two-stage directly connected amplifier is used as a preamplification stage for a bush-pull output amplification stage.

According to the present invention, a first differential amplifier including a differential pair transistor of a first conductivity type constituting a preamplification section (preamplification stage) of a power amplifier; By inserting a resistance means of a non-linear resistance in the power supply line between the second differential amplifier consisting of a differential pair transistor of the second conductivity type connected to the It is characterized by adjusting the bias current of the differential pair of transistors of the differential amplifier, thereby balancing the transient bias current of the bush-pull pair of transistors of the next-stage bush-pull output amplifier.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 shows a two-power supply OCL system (OutptCondens
er Less method) This shows a circuit diagram of a bush-pull power amplifier, in which the numbers in circles are the terminal numbers of the integrated circuit, and all the circuit elements within the broken lines are constructed within a single semiconductor chip by a well-known manufacturing method. There is.

First, a positive operating voltage B1 is supplied to the first positive voltage supply terminal ■, and a negative operating voltage -B is supplied to the negative voltage supply terminal [phase].
1 is supplied, this negative voltage supply terminal [phase] is electrically connected to the P-type substrate of the integrated circuit, and the differential pair transistors Q1. Q2. Q3. Q4 (NPN) transistor) Collector load resistance R1°R2, common emitter resistance R3
, and a constant current circuit 308, the first differential amplifier 11 responds to signals from the input terminal (■) and the negative feedback terminal (■).The first differential amplifier 11 includes a transistor Q5, a resistor R4, A constant current circuit 30 configured by
A bias current is provided by 8.

Next, a transistor Q6 of a conductivity type opposite to that of the differential pair transistors of the first differential amplifier. Q7 (PNP) transistor)
and resistors R5, R6, R7 are connected to each other to form a second differential amplifier 12, and a diode-connected transistor Q8 and a transistor Q9 form a differential pair of transistors Q6.
These differential transistors Q6.Q7 constitute a constant current load circuit. Connected to Q7.

Next, transistor Qll, Q121 Q13° diode D1. D2. D3 and resistor R1 constitute an emitter follower circuit 13.

Furthermore, the resistor R6, the diode-connected transistor QIO1, and the resistor R9 constitute a bias voltage 15, and the transistor QIO1 resistor R9 constitutes a bias voltage 15.
The bias voltage generated at the base electrode of transistors Q5 and Q13 biases the base electrodes of transistors Q5 and Q13, causing a constant current to flow through the collector-emitter paths of these transistors Qs and Q13.

Further, the first amplification section 303 and the second amplification section 304 respond to the firing signal of the emitter-emitter follower circuit 13, constitute a push-pull amplification stage 14, and constitute a push-pull output amplifier together with the emitter follower circuit 18.

The first amplification section 303 includes Darlington-connected transistors Q14. Q15, and is connected between the first positive voltage supply terminal ■ and the output terminal ■, and the second
The amplifying section 304 includes complementary connected transistors Q16. Q17, and is connected between the output terminal (2) and the negative voltage supply terminal [phase].

Furthermore, by connecting a negative feedback network 305 composed of a resistor R1□ and an R13 capacitor C3 between the output terminal ■ and the negative feedback terminal ■, DC-AC negative feedback is applied to the entire push-pull power amplifier. , the DC level of the output signal is maintained stably, and the distortion rate and frequency characteristics of the output signal are improved.

Furthermore, an oscillation prevention capacitor C is installed between terminal ■ and terminal ■.
6 is connected, AC negative feedback is applied between the base and collector of the differential transistor Q7 [phase] of the drive amplification stage 302, and phase compensation is performed.

In addition, the first positive voltage supply terminal ■ and the second positive voltage supply terminal ■
A power supply ripple removal filter circuit 306 constituted by a resistor R14 and a capacitor C5 is connected between the power supply ripple voltage at the first positive voltage supply terminal (2) and the first stage differential amplifier 11 and the second differential amplifier 12. and is configured to be attenuated and transmitted to the emitter follower circuit 13.

Furthermore, the constant current circuit 308 of the first stage differential amplifier 11 and the resistor R
A contact point J1 with 3 is connected to a ground terminal (2) via a low AC impedance means 309 constituted by a Zener diode ZD, and this ground terminal (2) is connected to a ground point.

Since the breakdown voltage Vz of this Zener diode ZD is set to a value sufficiently smaller than the absolute value of the negative operating voltage -B supplied to the negative voltage supply terminal [phase], this Zener diode ZD is in the breakdown region. Biased.

As a result, the ripple contained in the negative operating voltage source -B is reduced by the high AC impedance exhibited by the constant current circuit 308 and the low AC impedance exhibited by the Zener diode ZD, and the ripple is reduced in the differential pair transistors Q1 to Q4. Prevent it from being applied.

Furthermore, the distortion characteristic of the first differential amplifier 11 is improved by the action of the resistor R3 and the Zener diode ZD, which has a low AC impedance.

Further, according to the present invention, a resistor means 16 is inserted in the power supply line between the first differential amplifier (initial differential amplifier) 11 and the second differential amplifier 12.

This resistance means 16 is constituted by a forward biased PN junction diode formed by connecting the collector and base of an NPN transistor Q18.

According to the circuit configuration of the present invention, the object of the present invention is achieved for the following reasons.

That is, since the resistance means consisting of a PN junction diode is inserted between the power supply lines between the two-stage directly connected differential amplifiers 11 and 12, the power supply switches SW1. Because voltage is generated in the resistance means in the transient state when SW2 is turned on,
The voltage is the differential pair transistor Q of the second differential amplifier 12.
6. The fact that a bias voltage is applied between the base and emitter of Q7 means that the second differential amplifier 12
The output DC current flowing out from the output connection point J3 ■.

becomes large.

As a result, the collector current I flows through the emitter follower transistor Q1□ in the transient state when the power is turned on.

, 1° is the collector current ■ flowing through the constant current load transistor Q13.

Ql3, and as a result, the transient currents flowing through the output amplifiers 303 and 304 directly connected thereto are balanced, and the generation of pop noise can be prevented.

Also, if the resistance means 16 is removed, the power switch SW
1. In the transient state after SW2 is turned on, a current IQIO first flows through the bias circuit 15, and this current immediately becomes the collector current I of the load transistor Q13 of the emitter follower circuit 13.

The drive transistor Q1□ of the emitter follower circuit is connected to the first differential amplifier 11 and the second differential amplifier 12 in the preceding stage from the bias circuit 15.
4, its collector current I CQI□ increases more slowly after power-on, as shown in curve 2 of FIG. 4, than the increase in collector current I CQ13 shown in curve 1.

Therefore, as shown in FIG. 4, the collector currents of the two cause a difference of ΔIc in the transient state t1 when the power is turned on, and this difference current is amplified by the bush-pull output amplification stage 14, which is the cause of the popping noise. becomes.

According to the present invention, the generation of such popping sounds is prevented by inserting the resistance means 16, as described above.

As mentioned above, the insertion of the resistor means 16 results in the collector current of the transistor Q1□ in the transient state.

Both transistors Q1□ shown in FIG. 4 act in the direction of increasing Ql2.

The difference ΔIc in collector current of Ql3 can be made small.

If the rising voltage (forward voltage of the PN junction) of the PN junction diode Q18 used in the resistance means 16 is too large, the current flowing to the first differential amplifier during a transient period will cause the voltage to rise from the PN junction diode Q18 to the second differential amplifier. The applied bias voltage becomes large, and as a result, the current I CQI□ of transistor Q12
3. Current■.

Ql3 becomes overcompensated.

The collector current I is appropriate to prevent such an overcompensation condition.

Ql. 3, a resistor R16 can be connected in parallel with the PN junction diode Q18, as shown in FIG.

As a result, as shown in FIG.
can be varied to a characteristic as shown in characteristic curve 2.

Therefore, if the current applied to the resistance means 16 in a transient state is 11, the voltage generated in the resistance means 16 at that time can be changed from the diode-only voltage 1 to a lower voltage V2.

As a result, the differential pair transistor Q6 of the second differential amplifier.
Since the current flowing through Q7 can be adjusted to a small value,
Current I flowing through transistor Q12.

, 1□ is the current I of the transistor Q13.

It can be made small to balance Q-factor 3.

In the present invention, another effect when using a PN junction diode as the resistance means 16 is that the PN junction diode QI8 is used as the differential pair transistor Q of the second differential amplifier 12.
6. The advantage is that it can also be used as a temperature compensation element for Q7.

By using this PN junction diode, the differential pair transistor Q6. The bias current of Q7 is stabilized over temperature.

Furthermore, the use of this PN junction diode can reduce the voltage loss of the power supply voltage in a steady state.

As described above, the present invention is applied to prevent pop noises when the power is turned on when one of the amplifying elements constituting the bush-pull output stage is biased by the DC output of the preceding stage amplifier. The invention can be modified in various ways without departing from its spirit.

[Brief explanation of the drawing]

FIGS. 1 and 3 show an OCL constructed according to the present invention.
FIG. 2 is a characteristic diagram of the resistance means used in the power amplifier of the present invention, and FIG.
The figures each show characteristic diagrams used to explain the operation of the power amplifier of the present invention. 11: 1st differential amplifier, 12: 1 second differential amplifier, 13
: emitter follower circuit, 14: push-pull output amplification means, 15: bias circuit, 16: resistance means.

Claims (1)

[Claims] 1. A first differential amplifier including a first differential pair of transistors of a first conductivity type, and a first differential amplifier of a second conductivity type connected in direct current and alternating current to the output of the first differential amplifier. A push-pull output amplifier having a second differential amplifier including a second differential pair of transistors, and a pair of amplifying sections connected in a push-pull format connected to the output of the second differential amplifier in a direct current and an alternating current manner. In the power amplifier, the first amplifying section of the pair of amplifying sections of the push-pull output amplifier is provided with a DC bias current by the DC output current of the second differential amplifier, By inserting resistance means in the power supply path between the differential amplifier and the second differential amplifier,
A power amplifier characterized by preventing pop noises from occurring when the power is turned on. 2. In the power amplifier according to claim 1,
A power amplifier according to claim 1, wherein the resistor means includes a PN junction diode inserted so as to be biased in a forward direction with respect to the power supply path. 3. In the power amplifier according to claim 2,
A power amplifier characterized in that the resistance means includes the PN junction diode and a resistor connected in parallel with the PN junction diode. 4 In the power amplifier according to claim 1, 1
, a power amplifier characterized in that a speaker load is connected to the output of the push-pull output amplifier. 5. In the power amplifier according to claim 4,
A power amplifier characterized in that a negative feedback circuit network is connected between the output terminal of the push-pull output amplifier and the negative feedback terminal of the first differential amplifier.