JPH0946146A - Audio signal amplifier circuit driven at low voltage and sound equipment using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive the amplifier circuit at a low voltage by activating an output stage circuit of a class B push-pull operation so as to reduce signal distortion when the level of an output signal of an output stage circuit in a class A operation is a prescribed level or over. SOLUTION: An output stage circuit 12 is made up of transistors(TRs) Q30, Q31 configuring a class B push-pull output stage circuit, TRs Q32, Q33 configuring an output stage circuit of class A operation corresponding to a very small signal input, and drive circuits 15-18. Furthermore, an output current detection circuit 15a consisting of a current mirror 19 and a TR Q40 connected in parallel with the TRQ32 and an output current detection circuit 15a consisting of a current mirror 22 and a TR Q45 connected in parallel with the TRQ45 detect respectively collector currents of the TRs QA32, Q33. When a level of an output signal of the class A operation output stage circuit reaches a prescribed level or over, the output stage circuit of a class B push-pull operation is operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-voltage drive audio signal amplifier circuit and an audio device using the same, and more specifically to a portable magnetic tape player or portable CD (compact compact) driven by only one battery. The present invention relates to a low-voltage driven audio signal amplifier circuit in a portable audio device such as a disk player, in which signal distortion is unlikely to occur even when the idling current is reduced and power consumption can be reduced.

[0002]

2. Description of the Related Art Conventional portable magnetic tape players and portable CD players are driven by dry batteries, and the number of batteries is about 1 to 2. Therefore, the power supply voltage of the built-in audio circuit is 1.2V or 2.4.
Only about V. Moreover, in many cases, it has a stereo function, and its output stage circuit is of two systems. In such a portable audio device, there is a strong demand for one battery as a driving power source, and long-time performance is required. Therefore, it is desirable to reduce the idling current when there is no signal as much as possible.

FIG. 2 shows an example of an output circuit of this type of stereo audio amplifier circuit driven by one battery, and shows one channel on the left and right sides. Reference numeral 1 is an input stage circuit of an output circuit 5 which receives an input signal at an input terminal 3 to generate a drive signal, and 2 is an output stage circuit which generates a push-pull output to an output terminal 4. The output stage circuit 2 includes output transistors Q1 and Q2, diode-connected transistors Q3 and Q4 of a current mirror drive which are current mirror connected to these transistors, and a transistor which is connected between the emitter side of the transistor Q3 and the power supply line Vcc. It is composed of Q5 and a transistor Q6 connected between the emitter side of the transistor Q4 and the ground GND, and is driven by the output from the input stage circuit 1. Here, the transistors Q3 and Q4 and the transistors Q5 and Q6 (the bases thereof) are driven by signals from the input stage circuit 1 and signals having opposite phases to these signals, respectively.

At the time of signal input, depending on the phase of the signal input from the input stage circuit 1, during amplification of the positive half cycle, the upstream side transistor Q5 is turned off to suppress the idling current flowing through the transistor Q3. Only the transistor Q1 on the upstream side is operated. When amplifying the half cycle on the negative side, turn off the transistor Q6 on the upstream side.
To suppress the idling current of the transistor Q4,
Only the transistor Q2 on the downstream side is operated to reduce the idling current. When there is no signal, the transistor Q5 on the upstream side and the transistor Q6 on the downstream side are turned on by the output from the input stage circuit 1. As a result, a sufficient output current can be obtained even if the idling current when there is no signal is reduced.

[0005]

In the circuit for blocking the current flowing through the transistors Q3 and Q4 of the current mirror drive, the Vsat voltage (between the emitter and the collector) during the operation of turning on the transistors Q5 and Q6. Variations in the idling current flowing through the transistors Q3 and Q4. As a result, in an audio amplifier circuit driven by a low voltage, when the idling current varies toward the lower side, signal distortion increases. In order to prevent this signal distortion, the idling current is designed to be set high in advance,
In this case, there is a problem that the consumption current is further increased when the variation is higher. An object of the present invention is to solve the problems of the prior art as described above, and it is possible to reduce signal distortion, suppress variations in idling current, and suppress idling current. An object is to provide an audio signal amplifier circuit that can be driven at a low voltage and an audio device using the same.

[0006]

The features of the low-voltage driven audio signal amplifier circuit and the audio equipment using the same of the present invention for achieving the above-mentioned object are the first output of the class B push-pull operation. Stage circuit, second output stage circuit of class A operation, input stage circuit for generating signals for driving the first and second output stage circuits, and level of output signal of second output stage circuit And a drive circuit for operating the first output stage circuit when the level of the output signal becomes equal to or higher than a predetermined value upon receiving the detection signal from the detection circuit.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the first output stage circuit for class B push-pull operation and the second output stage circuit for class A operation are provided, and the output signal of the second output stage circuit is detected by the detection circuit. When a small signal less than a predetermined value is input, the second output stage circuit performs class A operation, and when a signal above the predetermined value is input, the first and second output stage circuits perform class B operation. Perform push-pull operation + Class A operation.

As a result, the idling current may be mainly composed of the second output stage circuit of the class A operation which operates when a small signal is input, so that a stable idling current without variation can be set, and the variation is not taken into consideration. Moreover, the idling current value can be set to a low value. Further, if the detection circuit is composed of a transistor in which the base terminal of the output transistor of the second output stage circuit and each terminal corresponding to one of the collector and emitter terminals are connected, the second output stage circuit Switching from the operation to the operation of the first output stage circuit plus the operation of the second output stage circuit to which the operation of the first output stage circuit is added is performed by the base terminal of the output transistor of the second output stage circuit and the collector and the emitter. Since it can be performed by the detection circuit including the parallel-connected transistors to which the respective terminals corresponding to any of the terminals are connected, it is possible to operate even at a low voltage. In addition, class A operation is performed at the time of a small signal, and class A operation is added and output for a signal input larger than that, so class A operation is mainly performed at a small input signal level. Therefore, even if the idling current is small, the crossover distortion as a whole can be suppressed small.

[0009]

1 is a block diagram centering on an audio output circuit of an embodiment to which an audio signal amplifier circuit of low voltage drive according to the present invention is applied. In FIG. 1, 10
Is a stereo audio circuit driven by one battery, and shows one channel of the left and right output circuits. The left and right output circuits have the same configuration. 11
Is an input stage circuit thereof, and 12 is an output stage circuit thereof. The input stage circuit 11 includes a differential amplifier 13 and a drive signal generation circuit 14. The differential amplifier 13 includes differential transistors Q10 and Q11, a constant current source 11a provided downstream of these transistors, and active loads Q12 and Q13 each of which is a diode-connected transistor inserted on the collector side thereof. , The base of the transistor Q10 receives an input signal from the preamplifier 30 via the input terminal 10a.

The drive signal generation circuit 14 includes a transistor Q on the upstream side whose emitter side is connected to the power supply line Vcc.
14, Q15, Q16, Q17, and transistors Q20, Q whose collectors are connected to the collectors of the respective transistors downstream of these and whose emitters are connected to the ground GND.
It has 21, Q22, and Q23. The transistors Q14, Q15, Q16, and Q17 on the upstream side are current-mirror connected to the transistor Q12 of the active load, and these transistors are driven in parallel. The transistors Q20, Q21, Q22, Q23 on the downstream side are current-mirror connected to the diode-connected transistor Q19 arranged on the downstream side,
A transistor Q18, which is current-mirror connected to the transistor Q13 of the active load, is provided upstream of the transistor Q19.
The output current is taken out through Q19, and the transistors Q20, Q21, Q22 and Q23 are driven in parallel.

Therefore, the connection point A where the collectors of the transistors Q14 and Q20 are connected to each other, and the transistors Q15 and Q21
Point B, where the collectors of the two are connected together, and transistor Q
Connection point C where the collectors of 16 and Q22 are connected, and connection point D where the collectors of transistors Q17 and Q23 are connected
It is possible to obtain four current outputs which are almost equal to each other. Output currents Ia, Ib, Ic, Id at these connection points
Thus, the drive circuits of the output stage circuit 12 provided corresponding to these are respectively driven. Output stage circuit 12
Are transistors Q30 and Q31 that form a class B push-pull output stage circuit, transistors Q32 and Q33 that form a class A output stage circuit corresponding to a minute signal input, and drive each transistor of these output stage circuits. Drive circuits 15, 16, 17, 18 for

The drive circuits 15 and 16 cancel the input current signal for driving the output stage circuit (transistors Q30 and Q31) of the class B push-pull by a predetermined value (Ith) by the current mirror, and further, this current value Ith. Is canceled by the detected current value Id from the transistor to generate a drive current in which the input current signal is reduced by the current value Ith−the detected current value Id. As a result, the cancel current value Ith is received by the current mirror.
B by the input current signal reduced by the current value Id from
It drives the output stage circuit of the class push-pull. Then, when the output value is a large input current signal exceeding the current value Id, the input current signal is directly added to the class B push-pull output stage circuit to be driven. On the other hand, the drive circuits 17 and 18
Drives a class A output stage circuit in accordance with an input current signal of each phase.

The drive circuit 15 comprises a drive transistor Q34, an output current detection circuit 15a, and a drive current cancel circuit 15b. The drive transistor Q34 is a push output side drive transistor having a collector connected to the base of the transistor Q30 and an emitter connected to the ground GND. Output current detection circuit 15
Reference numeral a denotes a transistor for detecting the collector current of the transistor Q32, which includes a transistor Q40 connected in parallel to the transistor Q32 and a current mirror 19. The collector of the current mirror 19 is a transistor Q.
It is connected to the collector of 40 and is arranged downstream of it, the emitter side is connected to the ground GND, and the detected current Id
It includes a diode-connected transistor Q41 for receiving and a transistor Q42 on the output side thereof.

The drive current cancel circuit 15b comprises a current mirror 20 and a constant current source 21 having a current value Ith. The current mirror 20 is a diode-connected transistor that receives the current value Ith from the constant current source 21 on its input side. It is composed of Q43 and an output-side transistor Q44 for shunting the drive current. The transistor Q44 has a collector side for sinking a current connected to the base of the transistor Q34, an emitter connected to the ground GND, and the current value Ith of the current signal Ic input from the connection point C to the base of the transistor Q34. To the ground GND. The base side of the transistor Q43 that receives the current value Ith is connected to the collector of the transistor Q42 on the output side of the current mirror 19, and the detected current Id is subtracted from the current value Ith. As a result, the current value of the current signal Ic input from the connection point C to the base of the transistor Q34 to be sunk to the ground GND becomes the current value Ith-Id. When the detected current Id exceeds the current value Ith of the current source 21, the transistor Q34 is driven by all of the current signal Ic input to the base of the transistor Q34, which drives the transistor Q30 and the upper half cycle. Signal is output. Here, the emitter area of the output transistor Q30 is m times the emitter area of the transistor Q34.

The drive circuit 16 comprises a drive transistor Q35, an output current detection circuit 16a, and a drive current cancel circuit 16b. The drive transistor Q35 is a pull output side drive transistor whose collector is connected to the base of the transistor Q31 and whose emitter is connected to the power supply line Vcc. Output current detection circuit 16a
Is a circuit similar to the output current detection circuit 15a, and differs from this in that the detected current becomes a sink current. This circuit is a transistor for detecting the collector current of the transistor Q33, and includes a transistor Q45 connected in parallel to the transistor Q33 and a current mirror 22. The current mirror 22 is composed of a diode-connected transistor Q46, whose collector is connected to the collector of a transistor Q45 located downstream and whose emitter is connected to the power supply line Vcc, and which flows out the detected current Id, and transistor Q47 on its output side. .

The drive current cancel circuit 16b is composed of a current mirror 24 and a constant current source 25. The current mirror 24 generates a diode-connected transistor Q48 for discharging a current value Ith to the constant current source 25 and an outflow current. Output side transistor Q49. In the transistor Q49, the collector side for discharging current is connected to the base of the transistor Q35, and the emitter is the power supply line Vcc.
Of the current signal Ib drawn from the base of the transistor Q35 at the connection point B, the current value Ith is discharged, and the current value Ith is subtracted. The base side of the transistor Q49 that discharges the current value Ith is connected to the collector of the transistor Q47 on the output side of the current mirror 22, and the detected current Id is similarly subtracted from the current value Ith by discharging. As a result, of the current signal Ib drawn from the base of the transistor Q35 by the connection point B, the current value added and discharged becomes the current value Ith-Id. And the current source 2
When the detected current Id exceeds the current value Ith of 5, the current signal drawn from the base of the transistor Q35 is all the signal current Ib, whereby the transistor Q35.
Are driven, and thereby the transistor Q31 is driven to output the signal of the lower half cycle. Here, the emitter area of the output transistor Q31 is M times the emitter area of the transistor Q35.

The drive circuit 17 comprises a drive transistor Q36, a transistor Q37 provided downstream of the drive transistor Q36, and a bias circuit 17a. The drive transistor Q36 has a current mirror connected to the base of the transistor Q32 via a resistor R1 and has an emitter connected to the power supply line V.
It is a transistor connected to cc, and its emitter area is 1 / n of that of the transistor Q32. The transistor Q37 is a transistor whose collector is connected to the collector of the upstream transistor Q36 and whose emitter is connected to the ground GND. The bias circuit 17a includes a constant current source 23 and a diode-connected transistor Q50 inserted between the constant current source 23 and the ground GND downstream of the constant current source 23. By supplying a constant current to the transistor Q50, a constant voltage is supplied to these connection points V1. The voltage at the connection point V1 is applied to the base of the transistor Q37 via the resistor R3 and is biased.

The drive circuit 18 comprises a drive transistor Q38, a transistor Q39 provided upstream thereof, and a bias circuit 18a. The drive transistor Q38 has a current mirror connected to the base of the transistor Q33 via a resistor R2 and has an emitter connected to the power supply line V.
It is a transistor connected to cc, and transistor Q39
Is a transistor whose collector is connected to the collector of the transistor Q38 and whose emitter is connected to the power supply line Vcc. The bias circuit 18a includes a constant current source 24 and a diode-connected transistor Q51 inserted between the constant current source 24 and the power supply line Vcc upstream of the constant current source 24. By supplying a constant current to the transistor Q51, a constant voltage is supplied to these connection points. The voltage at the connection point V2 generated at V2 is applied to the transistor Q via the resistor R4.
Bias this in addition to the 39 base.

Next, the operation will be described. First, when there is an input signal of the upper half cycle and the value of the detected current Id generated by this is smaller than the constant current Ith,
That is, when Ith <Id, a current of Ith-Id flows through the transistor Q43. Therefore, the current signal input from the connection point C to the base of the transistor Q34 is shunted by the transistor Q43 and the current mirror-connected transistor Q44 to divide the current Ith-Id into the ground signal.
Synced to ND. As a result, the drive signal generated at the connection point C is canceled by Ith-Id. The sink operation of Ith-Id by the transistor Q44 is It
This is performed until h = Id, and when Ith <Id, the input current signal is no longer synced. At this time, all the current signals input from the connection point C to the base of the transistor Q34 are added to the base of the transistor Q34, and the transistor Q30 is driven. As a result, the transistor Q3 is supplied in the range of Ith <Id according to the current signal input from the connection point C to the base of the transistor Q34.
0 operates, and as a result, the output on the push side is output terminal 1
0b.

Next, when there is an input signal of the lower half cycle and the value of the detected current Id generated thereby is smaller than the constant current Ith, that is, when Ith <Id, the current of Ith-Id. Flows through the transistor Q48.
Therefore, the current signal drawn from the base of the transistor Q35 by the connection point B is Ith-I among them by the transistor Q48 and the transistor Q49 in the current mirror connection.
The current for d is discharged. As a result, the drive signal generated at the connection point B is canceled by Ith-Id. The discharge operation of Ith-Id by the transistor Q48 is performed until Ith = Id as in the above.
When Ith <Id, the current signal is not discharged. At this time, the connection point B causes the transistor Q
All of the current signal drawn from the base of 35 is applied to the base of transistor Q35 to drive transistor Q31. As a result, from the connection point B to the transistor Q35
The transistor Q31 operates within the range of Ith <Id according to the current signal input to the base of the transistor Q1 to generate a pull-side output at the output terminal 10b.

Thus, for a large input signal that satisfies Ith <Id, a class B push-pull output stage circuit is formed in addition to the operations of the transistors Q32 and Q33 which form the class A output stage circuit. Transistor Q30,
The output operation of Q31 is performed. Note that, for convenience of explanation, the detected current value and the constant current value of the upper half cycle and the lower half cycle are described as Ith and Id with the same symbols, but they are substantially the same in operation. They may be the same, and do not necessarily mean the same current value.

In the drive circuits 17 and 18, the respective transistors Q37 and Q39 are driven according to the drive currents Ia and Id which are discharged or sinked at the connection points D and A, respectively, and the transistor Q36 is correspondingly driven. , Q38 operate to drive the respective output stage circuit transistors Q32, Q33 and the transistors Q36, Q38 to generate an output at the output terminal 10b in class A operation. The bases of the transistors Q32 and Q33 and the transistor 3
Resistors R1 and R2 are inserted between the bases of 6 and Q38, respectively, and the input signal level of the class A operation and the input signal level of the class B operation are set depending on the resistors R1 and R2 and the values of the resistors R3 and R4. Is adjusted. Further, resistors Rf1 and Rf2 are provided to apply voltage feedback from the output terminal 10b side to the base of the transistor Q11 of the differential amplifier 13.

In such a circuit, the idling current of the drive system at the connection points C and B for the signal for class B operation can be set to a value close to "0". Further, since the idling current of the drive system at the connection points D and A, which is the drive system of the class A operation of the minute signal system, is the amplification operation of the minute signal level, the bias circuits 17a, 1 described above are provided.
It can be limited to a small value by 8a, and the idling current has a small variation. Further, since the minute signal is performed in the class A operation, the signal distortion can be reduced. further,
With respect to a large input signal, the ON / OFF operation in the conventional current mirror drive is not necessary, so that it is not affected by the variation in the idling current.

The output current detection circuits 15a and 16a are composed of a current mirror having one stage of a transistor and a detection side transistor connected in series to the current mirror. The detection side transistor is connected in parallel with the output transistors Q32 and Q33. Therefore, the base of the transistor of the current mirror and the base of the transistor on the detection side are independent. Therefore, it is not necessary to perform the stacked bias on the base voltages of the two transistors. As a result, the forward voltage between the base and the emitter is 0.7 V and the collector-
The sum of the ON-sat voltage between the emitters, which is 0.2 V, is 0.
It can be operated with a power supply line Vcc voltage of about 9V.

[0025]

As described above, according to the present invention, the idling current may be mainly composed of the second output stage circuit of class A operation which operates when a small signal is input.
A stable idling current with no variations can be set, and the idling current value can be lowered without considering variations. In addition, the operation of the first output stage circuit + the second output stage circuit obtained by adding the operation of the first output stage circuit to the operation of the second output stage circuit is switched to the output transistor of the second output stage circuit. The operation can be performed at a particularly low voltage by using a detection circuit having a base terminal and a parallel-connected transistor to which each terminal corresponding to one of the collector and the emitter is connected. Also, when the signal is small, A
It is a class operation, and for a signal input larger than that, class B operation is added and output in addition to class A operation, so class A operation is the main at a small input signal level, so even if the idling current is Even if it is small, the overall crossover distortion can be suppressed small.

[Brief description of drawings]

FIG. 1 is a block diagram centering on an audio output circuit of an embodiment to which an audio signal amplifier circuit of low voltage drive according to the present invention is applied.

FIG. 2 is a block diagram centering on an audio output circuit of a conventional battery-powered audio device.

[Explanation of symbols]

1, 11 ... Input stage circuit, 2, 12 ... Output stage circuit, 3, 1
0a ... Input terminal, 4, 10b ... Output terminal, 5 ... Output circuit, 13 ... Differential amplifier, 14 ... Drive signal generation circuit,
15, 16, 17, 18 ... Drive circuit, 15a, 16
a ... Output current detection circuit, 15b, 16b ... Drive current cancellation circuit, 17a, 18a ... Bias circuit, Q1 to Q5
1 ... transistor.

Claims (4)

[Claims] 1. A first output stage circuit for class B push-pull operation, a second output stage circuit for class A operation, and first and second output stage circuits for driving these first and second output stage circuits, respectively. Second
Of the output signal of the second output stage circuit and the first drive circuit that receives the first drive signal and drives the second output stage circuit. A detection circuit for detecting, and a second operation circuit for receiving the detection signal and the second drive signal from the detection circuit and operating the first output stage circuit when the level of the output signal exceeds a predetermined value. A low-voltage drive audio signal amplification circuit including a drive circuit. 2. The detection circuit has a base terminal and a collector or emitter terminal corresponding to a base terminal, a collector or an emitter terminal of an output transistor of the second output stage circuit, respectively. The low-voltage driven audio signal amplifier circuit according to claim 1, further comprising a connected transistor, wherein the detection signal is obtained by the transistor. 3. The first and second drive signals are composed of two current signals whose phases are inverted, and the second drive circuit is forced to flow a current corresponding to the predetermined value. 2. The low-voltage driven audio according to claim 1, wherein the current mirror cancels the predetermined value by the current mirror, and the predetermined value of the current is canceled by the current value of the detection signal of the detection circuit. Signal amplification circuit. 4. A first output stage circuit for class B push-pull operation, a second output stage circuit for class A operation, and first and second output stage circuits for driving these first and second output stage circuits, respectively. Second
Of the output signal of the second output stage circuit and the first drive circuit that receives the first drive signal and drives the second output stage circuit. A detection circuit for detecting, and a second operation circuit for receiving the detection signal and the second drive signal from the detection circuit and operating the first output stage circuit when the level of the output signal exceeds a predetermined value. A drive circuit, and the detection circuit has a base terminal and a collector or emitter terminal corresponding to a base terminal, a collector or an emitter terminal of the output transistor of the second output stage circuit, respectively. And an audio signal amplifying circuit for obtaining the detection signal by the transistor.