JP3505325B2 - BTL amplifier circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a BTL amplifier circuit that prevents transistor saturation and achieves high output.

[0002]

2. Description of the Related Art Conventionally, as a power amplifier circuit, a BTL amplifier circuit is known in which signals having opposite phases are generated from an input audio signal and a load is BTL-driven by each signal. Such a BTL amplifier circuit is configured as shown in FIG. In FIG. 3, first, the connection point a of the drive transistors 4 and 5 and the connection point b of the output transistors 6 and 7 are commonly connected, and the connection point c of the drive transistors 8 and 9 and the connection point d of the output transistors 10 and 11 are connected. And are commonly connected.

In FIG. 3 having such a configuration, when a negative input signal is applied to the input stage amplifier 1, a negative signal is applied to the first input transistor 2 and a positive signal is applied to the second input transistor 3. Is applied. First input transistor 2
Is turned off in response to a negative signal, the driving transistor 4 is turned on and the driving transistor 5 is turned off. Therefore, the output transistor 6 turns on and the output transistor 7 turns off. When the second input transistor 3 turns on, the drive transistor 8 turns off and the drive transistor 9 turns on. Therefore, the output transistor 10 is turned off and the output transistor 11 is turned on. Therefore, the output current flows in the order of the output transistor 6, the load 12, and the output transistor 11.

When a positive input signal is applied to the input stage amplifier 1, a positive signal is applied to the first input transistor 2 and a negative signal is applied to the second input transistor 3. When the first input transistor 2 is turned on in response to a positive signal, the drive transistors 4 and 5 are turned off and on, respectively. Therefore, the output transistors 6 and 7 are turned off and on, respectively. When the second input transistor 3 is turned off in response to the negative signal, the drive transistors 8 and 9 are turned on and off, respectively. Therefore, the output transistor 10
And 11 are turned on and off respectively. Therefore, the output current flows in the order of the output transistor 10, the load 12, and the output transistor 7.

As described above, the output current flows in the order of the output transistor 6, the load 12 and the output transistor 11 or in the order of the output transistor 10, the load 12 and the output transistor 7, thereby causing the load 12 to pass through the BTL.
It is driving.

[0006]

By the way, the BT shown in FIG.
The saturation voltage on the power supply voltage side of the L amplifier circuit is Vce6 (sa
t), Vce4 (sat) + Vbe6, or Vbe4
It is determined by the maximum one of + Vce13 (sat). However, Vce6 (sat), Vce4 (s
at) and Vce13 (sat) are saturation voltages between the collector and the emitter of the output transistor 6, the driving transistor 4, and the current source transistor 13, and Vbe6 and Vbe
be4 is a base-emitter voltage of the output transistor 6 and the drive transistor 4. Here, since the output transistor 6 drives a load, the current supply capacity is set large, and the size of the output transistor 6 is large. Since the collector-emitter saturation voltage Vce (sat) decreases as the transistor size increases, Vce6 (sat) and Vb of the output transistor 6 are reduced.
e6 becomes smaller, and as a result, Vbe + Vce13 (s
at) is the largest. Therefore, the saturation voltage on the power supply voltage side of the BTL amplifier circuit is Vbe4 + Vce13 (sa
t). Further, based on the same idea, the saturation voltage on the power supply voltage side of the third and fourth output transistors 10 and 11 is the base-emitter voltage V of the drive transistor 8.
It is determined by be8 and the collector-emitter saturation voltage Vce14 (sat) of the current source transistor 14.

When the saturation voltage of the BTL amplifier circuit is determined as described above, the upper limit of the swing of the output signal is the power supply voltage Vcc.
To Vbe4 + Vce13 (sat) lower than the ground level Vbe8 + Vce14 (s)
It will be a value increased by at). Vbe + Vce (sa
Since t) is not negligible compared to the power supply voltage Vcc, BTL
There has been a problem that the full swing level of the output signal of the amplifier circuit is greatly limited, and the BTL amplifier circuit cannot achieve high output.

[0008]

SUMMARY OF THE INVENTION According to the present invention, first and second input transistors to which input signals having opposite phases are applied, and first and second input transistors which are driven according to an output signal of the first input transistor. A second driving transistor, a first current source transistor that supplies a bias current to the first and second driving transistors, and a SEPP connection, and a second driving transistor that is driven according to output signals of the first and second driving transistors. First and second output transistors, third and fourth drive transistors that are driven according to the output signal of the second input transistor, and second current source transistors that supply a bias current to the third and fourth drive transistors , SEPP connection, and third and fourth output transistors that are driven according to the output signals of the third and fourth drive transistors, A BTL amplifier circuit for BTL driving a load by the output signals of the first and second output transistors and the output signals of the third and fourth output transistors, and a connection point of the first and second output transistors, The connection point of the third and fourth drive transistors is connected, and the connection point of the third and fourth output transistors and the connection point of the first and second drive transistors are connected. To do.

A resistor connected between the first and second drive transistors and having a connection point connected to a connection point of the third and fourth output transistors, and the third and fourth resistors.
A resistor is connected between the driving transistors and is connected to a connection point of the first and second output transistors. According to the present invention, when the first and fourth output transistors are turned on, the voltage at the connection point of the first and second drive transistors is lowered, and when the second and third output transistors are turned on, the third and the third output transistors are turned on. The voltage at the connection point of the fourth drive transistor drops. Therefore, the voltage difference between the collector and the emitter of the first current source transistor, and the second
The voltage difference between the collector and the emitter of the current source transistor can be widened. Therefore, the saturation of the first and second current source transistors can be prevented, and the saturation voltage of the BTL amplifier circuit can be determined by the collector-emitter saturation voltage of the first and third output transistors.

[0010]

1 is a diagram showing an embodiment of the present invention, in which 15 and 16 are first and second output transistors 17 and 18 which are SEPP (single ended push-pull) connected. Are third and fourth output transistors connected in SEPP, and 19 and 20 are first and second
First and second drive transistors which respectively drive the output transistors and whose connection point a is connected to connection point d of the third and fourth output transistors 17 and 18,
Reference numerals 21 and 22 drive the third and fourth output transistors, and the connection point c thereof is connected to the connection point b of the first and second output transistors 15 and 16 so that the third and fourth output transistors are connected.
It is a drive transistor. In FIG. 1, the same elements as those in FIG. 3 are designated by the same reference numerals.

In FIG. 1, when a negative input signal is applied to the input stage amplifier 1, the output signal of the input stage amplifier 1 turns off the first input transistor 2 and turns on the second input transistor 3. Then, similarly to the operation described in FIG. 3, the first and fourth output transistors 15 and 18 are turned on. However, in this case, the connection point a between the first and second drive transistors 19 and 20 and the third and fourth connection points
The connection point d of the output transistors 17 and 18 is connected. When the fourth output transistor 18 is turned on, its collector voltage becomes a value close to the ground level.
Therefore, the emitter voltage of the first drive transistor 19 also has a value close to the ground level. First drive transistor 19
As the emitter voltage of V.sub.2 becomes a value close to the ground level, its base voltage becomes Vbe19 higher than the value close to the ground. However, Vbe19 is a base-emitter voltage of the first drive transistor 19. Therefore,
The voltage difference between the collector and the emitter of the first current source transistor 13 widens, and the first current source transistor 13 becomes difficult to saturate.

Also, the third and fourth drive transistors 21
And the connection point b of the first and second output transistors 15 and 16 are connected to each other.
When the output transistor 15 is turned on, the emitter voltage of the fourth drive transistor 22 becomes a value close to the power supply voltage Vcc. Therefore, assuming that the base-emitter voltage of the fourth drive transistor 22 is Vbe22, the collector voltage of the second input transistor 3 is a voltage lower than the power supply voltage Vcc by Vbe22. Therefore, the voltage difference between the collector and the emitter of the second input transistor 3 widens, and the second input transistor 3 is also less likely to saturate.

As the negative input signal becomes larger, the collector voltage of the fourth output transistor 18 becomes closer to the ground level, and the first output transistor 1
The collector voltage of 5 further approaches the power supply voltage Vcc, and the first current source transistor 13 and the second input transistor 3
The voltage difference between the collector and the emitter of is widened. Therefore, the first current source transistor 13 and the second input transistor 3 are less likely to be saturated.

Further, since a large output current flows through the load 12 according to a large input, the collector voltage of the first output transistor 15 increases and the collector voltage of the fourth output transistor 18 decreases due to the voltage drop of the load 12. However, the voltage difference between the collector and the emitter of the first and fourth output transistors 15 and 18 becomes small. This voltage difference is the first
When the voltage is lower than the collector-emitter saturation voltage of the fourth output transistors 15 and 18, the first and fourth output transistors 15 and 18 are saturated. Therefore, in the case of a negative input signal, the saturation voltage of the BTL amplifier circuit of FIG.
Determined by the saturation voltage between the emitters.

On the contrary, when a positive input signal is applied to the input stage amplifier 1, the output signal of the input stage amplifier 1 turns on the first input transistor 2 and turns off the second input transistor 3. Therefore, the second and third output transistors 16 and 17 are turned on. Here, the connection point c between the third and fourth drive transistors 21 and 22 and the connection point d between the first and second output transistors 15 and 16 are connected.
When the second output transistor 16 is turned on, its collector voltage becomes a value close to the ground level. For that reason,
The emitter voltage of the third drive transistor 21 also becomes a value close to the ground level. Since the emitter voltage of the third drive transistor 21 has a value close to the ground level, the base voltage thereof has a value higher than the value close to the ground by Vbe21. However, Vbe21 is the third drive transistor 2
1 is a base-emitter voltage. Therefore, the voltage difference between the collector and the emitter of the second current source transistor 14 increases.

The first and second drive transistors 19 are also provided.
And the connection point a of the third output transistor 17 and the connection point d of the fourth output transistor 17 are connected to each other.
When the output transistor 17 is turned on, the emitter voltage of the second drive transistor 20 becomes a value close to the power supply voltage Vcc. Therefore, assuming that the base-emitter voltage of the second drive transistor 20 is Vbe22, the collector voltage of the first input transistor 2 is a voltage lower by Vbe20 from a voltage close to the power supply voltage Vcc. Therefore, the voltage difference between the collector and the emitter of the first input transistor 2 is widened, and the first input transistor 2 is less likely to be saturated.

As the positive input signal becomes larger, the collector voltage of the second output transistor 16 approaches the ground level, and the collector voltage of the third output transistor 17 approaches the power supply voltage Vcc. As a result, the second current source transistor 14 and the first input transistor 2
Since the voltage difference between the collector and the emitter of the second transistor is further widened, the second driving transistor 14 and the first input transistor 2 are in a direction in which they are not saturated.

Further, since a large output current flows through the load 12 in response to a large input, the voltage drop of the load 12 causes the collector voltage of the third output transistor 17 to increase and the collector voltage of the second output transistor 16 to decrease. However, the voltage difference between the collector and the emitter of the second and third output transistors 16 and 17 becomes small. This voltage difference is the second
When the voltage becomes lower than the collector-emitter saturation voltage of the third and third output transistors 16 and 17, the second and third output transistors 16 and 17 saturate. Therefore, for a positive input signal, the saturation voltage of the BTL amplifier circuit of FIG.
Determined only by the saturation voltage between the emitters.

FIG. 2 is a diagram showing another embodiment of the present invention, in which 23 and 24 are first and second drive transistors 1.
9 and 20 are connected between the emitters of the resistors for adjusting the idling current, 25 and 26 are connected between the emitters of the third and fourth driving transistors 21 and 22, and
This is a resistor for adjusting the idling current. The connection point a ′ of the resistors 23 and 24 is connected to the connection point d, and the connection point c ′ of the resistors 25 and 26 is connected to the connection point b.

In FIG. 2, when the first and fourth output transistors 15 and 18 are on, the emitter current of the first drive transistor 19 flows through the resistor 23 to the fourth output transistor 18. First drive transistor 19
As the base voltage of the first driving transistor 19 increases and the currents flowing through the first and fourth output transistors 15 and 18 increase, the emitter current of the first driving transistor 19 tends to increase.
When this emitter current is about to increase, the base-emitter voltage of the first drive transistor 19 tends to expand. However, when the emitter current of the first drive transistor 19 increases, the voltage drop across the resistor 23 increases the emitter voltage of the first drive transistor 19. The rate of increase of the emitter voltage of the first drive transistor 19 is substantially the same as the rate of increase of its base voltage. Therefore, the first
The voltage difference between the base and the emitter of the driving transistor 19 remains unchanged, and the emitter current of the first driving transistor 19 does not increase.

On the other hand, a part of the collector current of the first output transistor 15 flows through the resistor 26 to the fourth drive transistor 22. The base voltage of the fourth driving transistor 22 decreases and the emitter current of the fourth driving transistor 22 tends to increase. When the current flowing through the resistor 26 increases, the voltage drop across the resistor 26 causes the emitter voltage of the fourth drive transistor 22 to decrease. Therefore, the fourth drive transistor 2
The voltage difference between the emitter and the base of 2 remains unchanged,
The emitter current of the drive transistor 22 does not increase.

Also, the second and third output transistors 16
And 17 are on, the third drive transistor 2
The base voltage of 1 rises and its emitter current tends to increase. When the current flowing through the resistor 25 is about to increase, the voltage drop across the resistor 25 also increases the emitter voltage of the third driving transistor 21, and the voltage difference between the base and the emitter of the third driving transistor 21 remains unchanged.
Therefore, the emitter current of the third drive transistor 21 does not increase.

When the base voltage of the second driving transistor 20 drops, its emitter current tends to increase. When the current flowing through the resistor 24 is about to increase, the voltage drop across the resistor 24 decreases the emitter voltage of the second driving transistor 20, and the voltage difference between the base and the emitter of the second driving transistor 20 remains unchanged. Therefore, the second
The emitter current of the drive transistor 20 does not increase.

Therefore, by inserting the resistors 23 to 24, the emitter current of each drive transistor can be changed. Therefore, there is another effect that the fluctuation of the idling current can be prevented and the deterioration of the distortion rate of the output signal of the BTL amplifier circuit can be prevented.

[0025]

According to the present invention, the saturation voltage of the BTL amplifier circuit can be determined by the collector-emitter saturation voltage of the output transistor, so that the full swing level of the output signal of the BTL amplifier circuit can be increased. Therefore, high output can be achieved. Also, especially when integrated,
Since the size of the output transistor becomes large, the collector-emitter voltage becomes small, and higher output can be achieved.

Further, since the resistance is inserted in the connecting portion between the drive transistors, it is possible to suppress the fluctuation of the idling current flowing in the drive transistors and prevent the deterioration of the distortion rate of the output signal of the BTL amplifier circuit. Play.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional example.

[Explanation of symbols]

2 First input transistor 3 Second input transistor 13 First current source transistor 14 Second current source transistor 15 First output transistor 16 Second output transistor 17 Third output transistor 18 Fourth output transistor 19 First drive transistor 20 Second drive transistor 21 Third drive transistor 22 Fourth drive transistor 23-26 resistance

Claims (2)

(57) [Claims] 1. A first and a second input transistor to which input signals having opposite phases are applied, a first and a second drive transistor driven according to an output signal of the first input transistor, and the first And a first current source transistor for supplying a bias current to the second driving transistor, and SEPP
First and second output transistors that are connected and that are driven according to the output signals of the first and second driving transistors, and third and fourth drives that are driven according to the output signals of the second input transistor A transistor and a second current source transistor for supplying a bias current to the third and fourth driving transistors, which are SEPP-connected, and which are driven according to output signals of the third and fourth driving transistors. An output transistor, and the output signals of the first and second output transistors and the third output transistor.
And load the BT by the output signal of the fourth output transistor
In a BTL amplifier circuit that drives L, a connection point of the first and second output transistors and a connection point of the third and fourth drive transistors are connected, and a connection point of the third and fourth output transistors And a connection point of the first and second drive transistors are connected to each other, a BTL amplifier circuit. 2. A resistor connected between the first and second drive transistors and having a connection point connected to a connection point of the third and fourth output transistors, and the third and fourth drive transistors. 2. The BTL amplifier circuit according to claim 1, further comprising a resistor connected to the first output transistor and a resistor connected to a connection point of the first and second output transistors.