JPH05308228A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To attain low power consumption and a low power supply voltage operation. CONSTITUTION:Output transistors(TRs) 54,50 are formed by serial connection of PNP, NPN TRs. When the output TRs 54,50 are activated, since TRs 52,48 in current mirror connection to them are turned off, a signal in response to an input signal becomes a base current for the output TRs 54,50. Thus, sufficient amplification is attained even when a mirror ratio of the current mirror is reduced and the idle current is decreased. Furthermore, since a PNP TR is adopted for the TR 54, the voltage drop is reduced and an output dynamic range is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit for push-pull amplifying an input signal, and more particularly to an amplifier circuit which increases current utilization efficiency and expands a dynamic range.

[0002]

2. Description of the Related Art Conventionally, push-pull amplifier circuits have been used in the output stage of audio equipment such as radios and tape recorders. Here, the basic configuration of this push-pull amplifier circuit is shown in FIG. The input signal supplied from the circuit in the previous stage is input to the pair of drive transistors 10 and 12, and the current flows through the current mirrors 14 and 16 in accordance with the current flowing through the drive transistors 10 and 12. Further, the current mirrors 14 and 16 are respectively connected to the transistor 1
4a, 14b and transistors 16a, 16b, the current flowing through the output side transistors 14a, 16a is obtained at the output terminal 20. The emitter areas of the input side transistors 14b and 16b and the output side transistors 14a and 16a in the current mirror are set to 1: N.
By setting (1:40), N-fold (40-fold) amplification can be performed.

On the other hand, in such a circuit, in order to prevent crossover distortion in the output transistors 14a and 16a, the transistor 14 forming a current mirror.
It is necessary to supply an idling current to a, 14b, 16a, 16b when there is no signal. In that case, when a current of 100 μA is applied to the input side transistors 14b and 16b of the current mirror, 4 m are applied to the output side transistors 14a and 16a.
The current of A will flow, and a considerable amount of current will be consumed.

On the other hand, audio equipment is often driven by a battery, and there is a demand to reduce power consumption as much as possible. Therefore, the present applicant has filed Japanese Patent Application No. 2-23043.
In No. 3, we proposed a circuit that can reduce this idling current. In this circuit, as shown in FIG. 3, the input side transistor 14 of the current mirrors 14 and 16 is
Switching transistor 1 on the emitter side of b, 16b
8 and 20 are arranged. The collectors of the control transistors 22 and 24 whose bases are commonly connected to the drive transistors 10 and 12 are connected to the bases of the switching transistors 18 and 20, respectively.

Therefore, when the transistor 10 is on, the transistor 12 is off, the transistor 24 is off, and the transistor 18 is off. Therefore, no current flows through the transistor 14b, and all the current flowing through the transistor 10 becomes the base current of the transistor 14a. Therefore, the current (= base current) flowing in the transistor 10 is amplified according to the current amplification factor of the transistor 14a and is obtained at the output OUT. At this time, the transistor 22 is also turned on, which turns on the transistor 20, but since the transistor 12 is turned off, current does not flow to the transistor 16b.
Even if the transistor 20 is turned on, there is no inconvenience.
When the transistor 12 is on,
Since the transistor 10 is turned off, the same operation is performed.

As described above, in the circuit of FIG. 2, the idling current is set by the mirror ratio of the current mirror,
The signal amplification is set by the current amplification factor of the output transistor. Therefore, it is possible to simultaneously achieve a small mirror ratio to suppress an idling current and a large current amplification factor to obtain a large output. It should be noted that the bias voltage setting circuit 25 includes the drive transistors 10 and 12
This is for setting the bias voltage of and the amount of idling current.

[0007]

However, according to the above-mentioned conventional example, the current mirrors 14 and 16 on the power source side are formed by NPN transistors. Output transistor 1
The residual voltage VCE of 4a is a large value determined by the sum of the base-emitter voltage VBE of the transistor 14a (usually about 0.6V), the base-emitter voltage VBE of the transistor 14b, and the collector-emitter voltage VCE of the transistor 10. Therefore, when the current voltage is low, there is a problem that the dynamic range cannot be sufficiently secured.

[0008]

According to the present invention, there is provided a first drive transistor driven by a first input signal, and a second drive transistor driven by a second input signal.
The diode-connected NPN transistor to which the output current of the first driving transistor is supplied, the output current-sinking output NPN transistor that is current-mirror connected to the diode-connected NPN transistor, and the output current of the second driving transistor are Diode connection P supplied
An NP transistor, an output current discharging output PNP transistor which is current-mirror connected to the diode-connected PNP transistor, and an emitter current of the diode-connected PNP transistor which is turned on / off in accordance with an output current of the first drive transistor. 1 switch means and 2nd switch means for turning on / off the emitter current of the diode-connected NPN transistor according to the output current of the second drive transistor.

[0009]

As described above, since the PNP type output transistor is used as the output transistor for discharging the output current, the voltage drop here can be made small and a sufficient dynamic range can be maintained at the output even when the power supply voltage is low. it can.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the overall configuration of the embodiment. In-phase input signals are input from the input terminals 30 and 32, and an amplified output signal is obtained at the output terminal 34.

The input terminal 30 has a PNP transistor 40 (driving transistor) 42 whose emitter is connected to a power source.
It is connected to the base of the (switch driving transistor), and the input terminal 32 is an NP whose emitter is connected to the base.
It is connected to the bases of N transistors 44 (driving transistors) and 46 (switch driving transistors).
The collector of the transistor 40 is a diode-connected (collector-base short-circuited) collector of an NPN transistor 48 (current mirror input side transistor), and an output NPN transistor 50 (collector is connected to the output terminal 34 and emitter is connected to ground). Suction output NPN
Transistor) is connected to the base. The collector of the transistor 46 is a diode-connected PNP.
An output PNP transistor 54 whose collector and emitter are connected to the power supply and whose collector is connected to the output end 34 of the transistor 52 (current mirror input side transistor)
It is connected to the base of (ejection output PNP transistor). Here, the transistor 48 and the transistor 5
0, and transistors 52 and 54 each form a current mirror.

On the other hand, the collector of the transistor 42 is connected to the collector of an NPN transistor 56 whose emitter is connected to ground and is diode-connected, and the base of an NPN transistor 58 which forms a current mirror together with this transistor. Also, the transistor 44
The collector of is connected to the collector of a PNP transistor 60 whose emitter is connected to the power supply and is diode-connected, and to the base of a PNP transistor 62 which forms a current mirror together with this transistor 60.

The collector of the transistor 58 is
It is connected to the base of a PNP transistor 64 (current source transistor) provided between the power supply and the emitter of the transistor 52, and the base of the transistor 64 is a resistor 6
It is connected to the power supply via 6. Also, the transistor 6
The collector of 2 is connected to the base of an NPN transistor 68 (current source transistor) provided between the ground and the emitter of the transistor 48.
The base of 8 is connected to ground via a resistor 70.

In such a circuit, the input terminals 30, 3
Since an appropriate bias voltage is applied to the transistor 2, a minute current corresponding to the bias voltage flows through the transistors 40 and 42 and the transistors 44 and 46 when there is no signal. Then, the current flowing through the transistor 42 causes a current corresponding to the transistors 56 and 58 forming the current mirror to flow, and this current flows through the resistor 66, so that the voltage at the base of the transistor 64 drops and the transistor 64 turns on. Become. On the other hand, when the current of the transistor 44 flows, a current flows through the transistors 60 and 62 forming the current mirror, and this current flows through the resistor 70, so that the voltage of the base of the transistor 68 decreases,
The transistor 68 is turned on.

When a current according to the bias voltage flows through the transistors 64 and 68, this current also flows through the transistors 52 and 48, and the current also flows through the transistors 50 and 54 that form a current mirror with the transistors 52 and 48, respectively. In this way, the idle current according to the bias voltage flows through each transistor, and crossover distortion can be prevented. Further, the idling current can be set to a predetermined value by setting the bias voltage and the characteristics of various elements to predetermined values.

Next, when a positive AC signal as shown in the drawing is input to the input terminals 30 and 32, the transistors 40 and 42 are turned off and the transistors 44 and 46 are turned on. When the transistor 42 is turned off, the transistor 5
No current flows through 6, 58 and the transistor 64 is turned off. Therefore, no current flows through the transistor 52. In this state, the input signal is applied to the base of the transistor 46, so that a current according to the input signal flows there. The current flowing through the transistor 46 becomes the base current of the transistor 54. Therefore, a current obtained by multiplying the base current by the current amplification factor of the transistor flows through the transistor 54, and an output signal is obtained at the output terminal 34.

On the other hand, when the transistor 44 is turned on, a current flows through the transistors 60 and 62, and the transistor 68
Turns on, but transistor 40 is off, so
No current flows through the transistors 48 and 50.

When a negative AC signal is input, the transistor 68 is turned off, and the current flowing in the transistor 40 becomes the base current of the transistor 50, which is amplified and generated as an output signal at the output terminal 34.

As described above, according to the circuit of this embodiment, the input signal can be used as the base current of the output transistors 50 and 54. Therefore, the transistors 48, 5
No. 2 can be used only for passing an idle current, and there is no problem even if the mirror ratio (input side: output side) of these current mirrors is reduced. It is preferable to set the current mirror ratio to about 1:10. Therefore, the transistors 48 and 52
The idle current of the transistors 50 and 54 can be made as small as about 1 mA when the idle current flowing through the transistor is set to about 100 μA.

In this embodiment, the transistors 52 and 54 are PNP transistors. Therefore, the collector potential of the transistor 54 is 0.3 V from the power supply voltage.
A sufficiently low value (conventionally about 0.6 V) can sufficiently operate. Therefore, it is possible to secure a sufficient dynamic range at a power supply voltage lower than the conventional one.

Further, for the operation of the transistors 64 and 68 which are the current sources of the transistors 52 and 48 which form the current mirror with the output transistors 50 and 54, a set of a current mirror and a resistor 66 composed of the transistors 56 and 58,
Alternatively, since a pair of the current mirror composed of the transistors 60 and 62 and the resistor 70 is used, by adjusting the resistance value,
The switching of the transistors 64 and 68 can be reliably performed at a potential close to the power supply or ground.

[0022]

As described above, according to the amplifier circuit of the present invention, the output stage transistor is composed of the PNP transistor and the NPN transistor in series, so that the remaining voltage in the discharge side PNP transistor can be made small and low. Sufficient operation is possible even at the power supply voltage.
Further, since the transistor that operates as a current source is also used for switching the operation of the output transistor, it is possible to reduce the number of elements and the circuit configuration becomes suitable when integrated into an integrated circuit (IC).

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a first conventional example.

FIG. 3 is a circuit diagram showing a configuration of a second conventional example.

[Explanation of symbols]

30, 32 input terminal 34 output terminal 40, 44 transistor (driving transistor) 42, 46 transistor (switch driving transistor) 48, 52 transistor (current mirror input side transistor) 50 transistor (suction output NPN transistor) 54 transistor (ejection) Output PNP transistor) 64, 68 transistor (current source transistor)

Claims (1)

[Claims] 1. A first drive transistor driven by a first input signal, a second drive transistor driven by a second input signal, and an output current of the first drive transistor are supplied. A diode-connected NPN transistor, an output current-sinking output NPN transistor that is current-mirror connected to the diode-connected NPN transistor, a diode-connected PNP transistor to which the output current of the second drive transistor is supplied, and the diode-connected PNP transistor. An output PNP transistor for discharging an output current, which is current-mirror connected to the transistor, first switching means for turning on / off an emitter current of the diode-connected PNP transistor according to an output current of the first drive transistor, Output power of driving transistor 2 Amplifier circuit and having a second switch means for turning on and off the emitter current of the diode-connected NPN transistors in accordance with the.