JPS58146108A - Power amplifier - Google Patents

Abstract

PURPOSE:To prevent the generation of spike noise at power supply switching, by avoiding a transistor (TR) for switching from being non-conductive in the switching of power supply voltage in response to the amplitude of input signal. CONSTITUTION:When an input signal amplitude is small, a diode 8a is inversely biased to be non-conductive, and a TR1a performs amplification by using a power supply voltage +V1. since a TR7a amplifies the input signal and supplies the output to a load 3 via a by-pass circuit 14a, then the TRs 1a, 7a perform amplification in parallel. When the signal amplitude is large, the diode 8a is conductive and a diode 5a is inversely biased, then the power supply voltage in response to the amplitude of the input signal is applied to the TR1a from the TR7a via the diode 8a. Thus, since the TR7a is not non-conductive through the switching, no spike noise is generated. This applies also to the negative power supply side.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a power increase #Ia &
: Relevance, special & : iI source voltage [Switching noise when switching [Regarding the gravitational field** that was designed to reduce] Conventionally, as a power amplifier for audio, the power amplifier increases - T according to the amplitude of the signal. It is known that the power supply voltage supplied to the amplifier element in the output stage is switched, thereby reducing the loss of the amplifier element and increasing the power efficiency. FIG. 1 is a circuit diagram showing an example of such a power amplifier.

In this figure, the NPN transistor 1a and the PNP transistor 1b constitute a push-pull output stage amplifier circuit, which push-pull amplifies the input signal (signal with amplification T) supplied to the input terminal 8 and sends it to the load 8. Supply Truyo &: Suruturu. The collectors of these transistors la and lb are supplied with the power supply voltage +v1 of the power supply 4m and the power supply voltage -v of the power supply 4b through diodes 6M and 6bf, respectively, and the power supply voltage +■1 of the power supply 4a and The power supply voltage of the power supply 6a +■2, the added power supply voltage +■day, the power supply voltage of the power supply 4b -■, and the power supply voltage of the power supply 6b -■
! The power supply voltage -V, which is the sum of PNP) are supplied via each transistor Wb.
It has become so.

In this case, the transistors qa and 7b are made to conduct in accordance with the amplitude only in a region where the amplitude of the input signal exceeds a predetermined amplitude, and therefore, the amplitude of the input signal is smaller than the predetermined amplitude. In this case, transistor 1a
, 1b, each collector voltage +Vss-Vs is +V, ,
-V, and when the amplitude of the input signal exceeds the predetermined amplitude, the collector voltage +v8, -V becomes +v,
, -vHt'', each with an upper limit, T varies depending on the amplitude of the input signal. When the signal voltage rtee is set, the collector voltage of transistors Ha and Ib +■5l-V8 is @
It changes as shown in Figure 2.

By the way, in the conventional power amplifier configured in this way, at the point in time when the amplitude of the amplified T signal exceeds the predetermined amplitude (for example, time 1...1 in @2 diagram).
) Langista? When a and (Wb) start conducting, the collector current of the same transistor 7m and (Wb) increases rapidly,
At the time when the amplitude of the increased 11t#T signal decreases below the predetermined value (for example, time 1..1 in FIG. 1), the transistors 7a and 7b are in a non-conducting state 11A. Is it the same transistor? a, (7
The collector current in b) suddenly becomes zero. Once upon a time, in such a conventional power amplifier, l! Time LH in Figure 2, t! , ta, 14, when the power supply voltages supplied to the transistors la and lb are switched &, , the transistors 7a and 7a as described above are switched.
Due to the switching action of 7b, there is a problem in that spike noise as shown in the figure is added to the output signal (e,) (that is, switching distortion occurs).

In view of the above points, the present invention provides a power amplifier that can prevent the occurrence of spike noise when switching the power supply voltage and reduce switching distortion of the output signal. A transistor I and a transistor A are provided, and when the amplitude of the input signal is small, the input signal is amplified in parallel by both the transistor FAL and the transistor FAL. When the amplitude of the signal is large, the input signal is mainly amplified by the first transistor, and the power supply voltage is supplied to the transistor @/ via the second transistor, and the magnitude of lkNM of the input signal is adjusted. The feature is that all transistors are prevented from becoming non-conductive regardless of the situation.

An embodiment of the present invention will be described below with reference to drawings. FIG. 3 shows a -m configuration example of a power amplifier according to the present invention.
It is a circuit diagram. In this figure, 2 is the amplified T signal (
This is an input terminal to which an input signal) is supplied, and the input signal supplied to this input terminal 2 is connected to the bases of NPN) transistors la (first amplification element) and NpN) transistors m (first amplification element), respectively. Supplied. In fact, these transistors are 1M, ? A bias circuit is inserted between the paces a. The collector (K source input terminal) of the transistor 7a is on the positive side of the power supply 6a 4I:M!
The emitter is connected to the collector (power supply input terminal) of the transistor la through a diode 8a (@ diode) in the tlli direction, and is connected to the output terminal 11 through a parallel connection circuit of a resistor 9a and a capacitor 10a. It is connected to the. Is the collector of transistor Ia a diode? 1jl (first diode) [Connected in the opposite direction to the connection point between the negative terminal of the power supply 61 and the positive terminal of the power supply 4a, and the emitter is connected to the output terminal 1 through the resistor IBa.
It is tied to 1. A G load B is inserted between the output terminal 11 and the ground terminal 1B, and the negative @ of the power supply 4a is inserted.
The terminal is grounded. The parallel connection circuit of the resistor 9a and capacitor loa is increased by the F transistor a.
A bypass circuit 14a is configured to supply the signal to the load 8&:. Note that the negative power supply side circuit in this embodiment has a complementary configuration to the positive power supply m circuit described above.

Next, the operation of the power amplifier having the above configuration will be explained. First, the operation of the positive power supply circuit will be explained. Now input terminal 2
The amplitude of the input signal supplied to transistor 7 is small.
If the emitter potential of a is lower than the power supply voltage +vi of the power supply 4a, the diode 8a is reverse biased and non-conductive. Therefore, in this case, the collector of the transistor la is connected to the diode 6! from the power supply 4a. A power supply voltage +vl is supplied through lt-, and the transistor 1a amplifies the input signal using this power supply voltage +1 and supplies it to the load 8 through the output resistor 12a. In this case, the input transistor 7a also amplifies the input signal and supplies this output to the load 8 via the bypass circuit 14art, that is,
If the amplitude of the input signal is smaller than the predetermined amplitude determined by the voltage +■, the input signal is supplied to the load B with an increase @gn in parallel by the transistor Ia and the transistor 7!1. And in this case, the transistor 1m,
? The distribution of the current flowing through a is determined by the ratio of the resistance of the resistor 1m and the impedance of the bypass circuit 14a.Next, when the amplitude of the input signal is larger than the predetermined amplitude, the emitter potential of the transistor 7a is Power supply voltage +v1
Since the voltage becomes higher, diode 81 becomes conductive, and diode 6a is reverse biased and becomes non-conductive. Therefore, in this case, a power supply voltage corresponding to the amplitude of the input signal is supplied to the collector of the transistor la from the transistor 7m via the diode 8a. Then, the transistor ta amplifies the input signal using this power supply voltage and supplies this output to the load B via the resistor lza.Also, in this case, the transistor ta amplifies the input signal to the collector of the transistor la as described above. At the same time, as in the case where the amplitude of the input signal is small, the power supply voltage T72 (the amplified output of the input signal output from the transistor 7a) is increased via the bypass circuit 14a.
[Supplied to load 8]

Note that the negative power supply side circuit in the T power axis multiplier shown in FIG. 3 performs a complementary operation to the positive power supply side circuit described above.

As described above, according to this embodiment, when the amplitude of the input signal is smaller than the predetermined amplitude, the transistors 1M, (l
b) and transistor 7a% (Wb) amplify the universal signal in parallel and supply it to load 3, -f of the universal signal.
! If the width exceeds the predetermined amplitude, the transistors la and (lb) amplify the signal and supply it to the load 8, and the transistor ? a, (7b) are transistor 1
m, (lb) to the collector of these transistors la
, (lb) is not saturated, a thicker qt power supply voltage is supplied. According to this embodiment, a current corresponding to the amplitude of the input signal flows through the transistors 7a and Wb even when the amplitude of the input signal is smaller than the predetermined amplitude. or the predetermined amplitude
b is the power supply voltage to the transistors 1a, 1b [Even when the supply starts or stops, the same transistors qm, 7
The current flowing through b does not change suddenly as in conventional power amplifiers, and therefore no spike noise is added to the output signal.

In addition, in the embodiment described above, the capacitors lea,
Each bypass circuit 14a using lOb.

14 b Since it is 1F-1fE, it is the transistor 7a.

7b performs a signal amplification operation, if the frequency of the input signal is high, the impedance of each bypass circuit 14a, t+b decreases, and the transistor? a.

It may seem that the power efficiency decreases due to the increase in the emitter current of Fb, but the decrease in efficiency is almost ignored since the actual music signal etc. is a composite signal made up of high frequency components and low frequency components. As much as possible.

As explained above, the power amplifier according to the present invention has a power supply voltage I81 supplied to the power supply input terminal via the first diode, and a first amplification element which amplifies the input signal and supplies it to the output terminal. , the lIl! at the power input terminal. a second amplifying element to which a power supply voltage of @- higher than the power supply voltage of fIn is supplied and which amplifies and outputs a signal T corresponding to the input signal; II! is supplied to the power input terminal of the amplifier element. This diode and the ll! Since a bypass circuit and t' are provided to supply the output of the booster element to the output gate, the amplitude of the input signal is small.
Even in the case of 1B2, a current corresponding to the amplitude of the power signal flows through the amplification element of 1B2, and as a result, spike noise is prevented from occurring when switching the power supply voltage, and switching distortion of the 1 output signal is reduced. can be done.

[Brief explanation of drawings]

FIG. 1 is a T circuit diagram showing a -II configuration example of a conventional power amplifier;
FIG. 1 is a waveform diagram for explaining the rotation operation, and FIGS. 1 to 3 are circuit diagrams showing one embodiment of the power amplifier according to the present invention. IJI, lb... II/ amplifier element (transistor), 6a, 6b... First diode (diode), 7a, ? b...First amplification element (
Transistors), 8a, 8b... IIJ diode C diode) -14a, 14b... Bypass circuit.

Claims (1)

[Claims] 11 at the power input terminal! The power supply voltage of / is supplied via the diode of II/, and the input signal is amplified and supplied to the output terminal by the amplification element of T@/, and the power supply voltage of I! is supplied to the power input terminal of the amplifier. The amplification element 1 is supplied with a power supply voltage higher than the power supply voltage of I!, and amplifies and outputs a signal corresponding to the human input signal, and this I! A power amplifier comprising: a diode S which supplies the output of the amplifying element 1 to the power input terminal of the amplifying element 112, a bypass circuit which supplies the output of the 112 amplifying element to the output terminal; .