JPH0332243B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage switching type amplifier circuit that improves efficiency and distortion rate.

Conventionally, a voltage switching type amplifier circuit that can obtain higher efficiency than a class B power amplifier circuit has been constructed as shown in FIG. 1, taking a push-pull amplifier circuit as an example. In other words, low voltage power supply +V _L (-
Output transistors 1 and 1' are connected to V _L ) to drive a load, and output transistors 2 and 2' are connected to a high voltage power supply +V _H (-V _H ) to drive a load.
and a comparator (not shown) that compares the input signal voltage with a preset voltage (hereinafter referred to as a comparison voltage);
Switch means 3, 3' are turned on by the output of the comparator when the input signal voltage is below the comparison voltage, and lead the input signal to the output transistors 1, 1'; It consisted of switch means 4, 4' which are turned on by the output of the comparator and guide the input signal to the output transistors 2, 2'. Note that 5 is a drive circuit.

According to the conventional voltage switching type amplifier circuit configured as shown in FIG. 1, the output transistor is switched depending on the magnitude of the input signal voltage. The efficiency was higher than that of the class B power amplifier circuit.

However, the conventional amplifier circuit described above has the drawback that switch distortion occurs when switching from an output transistor connected to a low voltage power supply to an output transistor connected to a high voltage power supply, resulting in poor characteristics. . Also, at low frequencies, there is sufficient negative feedback, so the distortion rate does not deteriorate much, but at high frequencies, the amount of feedback decreases due to phase compensation, etc., making it difficult to improve the distortion rate. .

The present invention has been made in view of the above, and it is an object of the present invention to provide an amplifier circuit that eliminates the above-mentioned drawbacks.

Hereinafter, the present invention will be explained by examples.

FIG. 3 is a block diagram of one embodiment of the present invention, and is an example in which the present invention is applied to a push-pull amplifier circuit.

In the figure, the same components as in FIG. 1 are denoted by the same reference numerals.

The input signal voltage amplified by the drive circuit 5 (hereinafter referred to as
An output transistor ₁ is connected to the low voltage power supply +V _L to drive the load, and an output transistor 2 is connected to the high voltage power supply +V _H to drive the load through switching means 3 and 4, respectively. The input signal voltage V _i is applied as the voltage to be compared to the comparator 6, which is connected to the comparator 6 so as to apply it to each separately, and the comparison voltage is the voltage of the power supply 12. When the input signal voltage V _i is less than the voltage of the power supply 12, the switch is activated. Means 3 is turned on, and input signal voltage V _i is set to power supply 1.
When the voltage exceeds 2, the switch means 4 is turned on.

Furthermore, in this embodiment, the input signal voltage V _i is connected between the comparator 6 and the switch means 3 and 4 from the power supply 1.
When the voltage exceeds 2, a time constant circuit 7 and a holding circuit 8 are connected to keep the switch means 4 in the on state for a certain period of time, and the output voltage of the holding circuit 8 is compared with the comparator 6. A positive feedback circuit 9 is connected to the voltage input terminal to provide positive feedback to reduce the comparison voltage of the comparator 6 to a voltage lower than the voltage of the power supply 12, so that the comparator 6 is configured to have hysteresis characteristics.

Note that although only the part that operates during the positive period of the signal applied to the input terminal IN in FIG. 3 has been described above, the structure of the part that operates during the negative period of the signal is the same, and Components corresponding to the figures are indicated by the same reference numerals with the suffix '.
Furthermore, since the operation of the portion operating during the negative period of the signal applied to the input terminal IN is similar to the operation of the portion operating during the positive period, the latter case will be described.

This embodiment configured as above is the same as the case shown in FIG. 1 except for the time constant circuit 7, holding circuit 8, and positive feedback circuit 9, and the input signal voltage V _i is If the voltage is below 12, the comparator 6 turns on the switch means 3,
A load is driven by the output transistor 1. If the output voltage Vo is Vo=E _n sin θ, the efficiency in this case is expressed as πE _n /4V _L. Furthermore, when the input signal voltage V _i exceeds the voltage of the power supply 12, the load is driven by the output transistor 2, and the efficiency in this case is becomes. Therefore, the efficiency becomes as shown by curve a in FIG. 2, which is higher than that of the conventional class B amplifier circuit.

However, by providing the time constant circuit 7 and the holding circuit 8 in this embodiment, the input signal voltage V _i
The peak value of the power supply 1 is used as the comparison voltage of the comparator 6.
When the voltage exceeds 2, the holding circuit 8 maintains the switch means 4 in the on state for a certain period of time determined by the time constant of the time constant circuit 7.

Therefore, for high frequency signals, the input signal voltage
When V _i is a continuous signal greater than the voltage of the power supply 12, the switch means 4 is kept on, the switch means 3 is kept off, and the output transistor 2 operates to drive the load. In this state, the circuit performs the same operation as a normal class B amplifier circuit, and the distortion rate is also improved.

However, if only the time constant circuit 7 and the holding circuit 8 are provided, a ripple component is superimposed on the comparison voltage, and if the peak value of the input signal and the comparison voltage are close to each other, the ripple component As a result, the output of the comparator 6 repeatedly turns on and off and fluctuates, resulting in a point where it is impossible to determine whether the input signal voltage V _i is large or small. At this point, the distortion rate will deteriorate. However, in this embodiment, since the positive feedback circuit 9 is connected, the apparent gain of the comparator 6 increases, and at the same time, the time constant circuit 7 and the holding circuit 8 work to turn on the switch means 4. Afterwards, the comparison voltage of the comparator 6 is set to a value lower than the voltage of the power supply 12 by the positive feedback circuit 9, and the comparator 6 exhibits hysteresis characteristics, and the peak value of the input signal voltage V _i is set to a value lower than the voltage of the power supply 12. The holding circuit 8 operates until the voltage drops below a comparison voltage which is lower than the voltage of 12. Therefore, the comparison voltage of the comparator 6 is different when the input signal voltage V _i increases and when it decreases, and in the former case the comparison voltage is high and equal to the voltage value of the power supply 12, and in the latter case is set to a voltage lower than the voltage value of the power supply 12 by the positive feedback circuit 9, so that the fluctuation in the output of the comparator 6 mentioned above disappears and there is no point where the distortion rate becomes worse.

Therefore, the distortion rate in the conventional voltage switching type amplifier circuit shown in FIG. 1 is improved, and good distortion rate characteristics that are almost the same as the distortion rate of a general class B amplifier circuit can be obtained. In addition, in the case of a high-frequency, large-amplitude input signal voltage _Vi , the output transistor 2 works to achieve the same efficiency as a normal class B amplifier circuit, but in actual music signals, etc., as the frequency increases, As a result, the amount of energy decreases, and in the low frequency range, it has high efficiency characteristics similar to the conventional voltage switching type amplifier circuit, so the efficiency of the amplifier circuit of this example is actually as shown in Figure 1. This value is close to the efficiency of the conventional voltage switching type amplifier circuit shown.

In the above description, the voltage to be compared of the comparator 6 is obtained from the drive circuit 5, but the same effect can be applied even if the voltage at the output terminal OUT is applied to the comparator 6 as the voltage to be compared by the comparator 6.

Next, a specific circuit according to an embodiment of the present invention will be explained.

FIG. 4 is a circuit diagram of a specific circuit according to an embodiment of the present invention.

13, 13' are transistors corresponding to the switch means 3, 3', and 14, 14' are transistors corresponding to the switch means 4, 4'. 16,
16' is a transistor constituting the comparators 6, 6', and 191, 191' and 193, 19
3' constitutes a voltage divider circuit that divides the power supply voltage V _L (-V _L ), and the output voltage of this voltage divider circuit is connected to resistors 20 and 2.
0' to the bases of the transistors 16, 16' to provide a comparison voltage corresponding to the power supplies 12, 12' of the comparators 6, 6'. 171, 171' and 172, 172' are resistors and capacitors forming time constant circuits 7, 7'. 18, 18' are transistors forming the holding circuits 8, 8';
192, 192' are resistors forming a positive feedback circuit together with resistors 191, 191' and resistors 193, 193'.

The input signal voltage V _i is connected to the output transistors 1 and 1' through transistors 13 and 13', and the bases of the transistors 13 and 13' are connected to the resistor 2.
High voltage power supply of opposite polarity through 1, 21' - V _H
(+V _H ), and input signal voltage V _i is connected to output transistors 2 and 2 through transistors 14 and 14'.
2', and the transistors 14, 1
The collector of 4' is connected to the bases of transistors 13 and 13'. Therefore, transistors 14,1
When 4' is off, transistors 13,1
3' is always on, and the transistors 14,
When 14' is on, transistors 13,1
Between the emitter and base of 3' is the transistor 14,
Since the emitter and collector of the transistor 14' are connected to each other, the transistors 13 and 13 are turned off. Therefore, it is only necessary to turn on and off the transistors 14 and 14' depending on the magnitude of the input signal voltage V _i , and it is sufficient to turn on and off the transistors 14 and 14'.
By turning off the transistors 13 and 13', on/off is controlled.

On the other hand, the bases of the transistors 14, 14' are connected to the emitters of the transistors 16, 16' through diodes 22, 22', 23, 23', and the collectors of the transistors 16, 16' are connected to the capacitor 1.
High voltage power supply of opposite polarity through 72, 172'
Connect to V _H (−V _H ). transistor 18,1
The base of transistor 8' is connected to the collector of transistor 16, 16' through resistor 171, 171', and the collector of transistor 18, 18' is connected to diode 2.
The transistor 1
The emitters of 8 and 18' are connected to high voltage power supply with opposite polarity.
Connect to V _H (+V _H ).

Note that the diodes 22, 22', 23, 23',
24, 24', 25, 25', 26, and 26' are diodes for blocking backflow.

In the specific circuit of one embodiment of the present invention configured as described above, the input signal voltage V _i is equal to the power supply voltage.
When the voltage is lower than the voltage obtained by dividing V _L by resistors 191 and 192, transistor 16 is in an off state and transistor 14 is also in an off state. Therefore, the transistor 13 is turned on, the input signal voltage V _i is applied to the output transistor 1 and amplified, and the load is driven by the output transistor 1. The input signal voltage V _i increases and transistor 16
When the voltage applied to the base of V i is exceeded, the transistor 16 turns on, and as the transistor 16 turns on, the transistor 14 turns on, and the input signal voltage V _i is applied to the output transistor 2 through the transistor 14. The load is driven by the output transistor 2. At the same time as the transistor 14 turns on, the transistor 13 turns off as described above, and the application of the input signal voltage to the output transistor 1 is cut off.

Further, since the transistor 16 is turned on, the capacitor 172 is charged by the collector current of the transistor 16, and the capacitor 172 is charged by the collector current of the transistor 16.
The voltage across terminals 2 increases and transistor 18 turns on. Therefore, in this state, even if the input signal voltage V _i decreases, the resistor 171 and capacitor 172
The transistor 18 remains on for a certain period of time determined by a time constant. Therefore, as explained in the block diagram of FIG. 3, the output transistor 2 continues to drive the load, performs the same operation as a general class B amplifier circuit, and improves the distortion factor.

Furthermore, since the transistor 18 is turned on, the potential at the common connection point between the resistors 191 and 193 is pulled toward the power supply voltage -V _H side via the resistor 192, the diode 24, and the transistor 18, and thus decreases. Lower the base potential of 16. Therefore, the input signal voltage V _i decreases to turn off the transistor 16 _.
The value of decreases, and the comparison voltage of the comparator 6 decreases, which is equivalent to the case where the comparator 6 has a hysteresis characteristic. When the input signal voltage V _i drops below the reduced base voltage of the transistor 16, the transistor 16 is turned off, and then the resistor 171
The transistor 18 remains on for a time determined by the time constant of the capacitor 172 and the transistor 18, and after this time the transistor 18 is turned off, the transistor 14 is turned off, and the transistor 13 is turned off.
will switch to the on state.

Further, the same applies to the portions indicated by ' that operate during the negative period of the signal applied to the input terminal IN.

Therefore, the effect of the specific circuit shown in FIG. 4 is the same as that explained using the block diagram of FIG. Almost the same efficiency as a voltage switching type amplifier circuit can be obtained.

In addition, in the above explanation, a case has been explained in which both a time constant circuit, a holding circuit, and a positive feedback circuit are provided. By simply doing so, the deterioration of the distortion factor due to the wandering of the comparator output when the input voltage is close to the comparison voltage is eliminated.

As explained above, according to the present invention, in a voltage switching type amplifier circuit, there is a means for giving a hysteresis characteristic to a comparator, and after the input signal voltage or output voltage exceeds the comparison voltage, the input signal voltage or the output voltage decreases. By providing a means for maintaining an on state of a switch means for applying an input signal voltage to an output transistor connected to a high voltage power supply and driving a load for a certain period of time when Similar high efficiency can be obtained, and the distortion rate can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining a conventional amplifier circuit. FIG. 2 is a characteristic diagram showing the efficiency of the amplifier circuit of FIG. 1. FIG. 3 is a block diagram of one embodiment of the present invention. FIG. 4 is a specific circuit diagram of one embodiment of the present invention shown in FIG. 3. 1, 1', 2 and 2'...output transistor,
3, 3', 4 and 4'... switch means, 6 and 6'... comparator, 7 and 7'... time constant circuit,
8 and 8'...holding circuit, 9 and 9'...positive feedback circuit.

Claims (1)

[Claims] 1 A first power source connected to a first power source and driving a load.
a second output transistor that is connected to a second power source that outputs a voltage greater than the absolute value of the voltage of the first power source and drives a load; a comparator for comparing with a comparison voltage set in advance as a comparison voltage; and a first switch means for guiding the input signal voltage to the input terminal of the first output transistor when the voltage to be compared does not exceed the comparison voltage. ,
and a second switch means connected to the comparator for guiding the input signal voltage to the input terminal of the second output transistor when the compared voltage exceeds the comparison voltage. A time constant circuit, a holding circuit connected to the time constant circuit, and a feedback circuit that positively feeds back the output of the holding circuit to the comparator to give the comparator a hysteresis characteristic. Amplification circuit.