JPH046130B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier circuit, and more particularly to a class A power amplifier circuit used in audio equipment and the like.

Amplifiers for driving loads such as speakers include class A and class B SEPP (single-ended push-pull) amplifier circuits. In a class A amplifier circuit, a pair of output amplifying elements always operate in the active region and never shift to the cut-off region, so there is no distortion due to switching. This has the disadvantage that heat loss is large and efficiency is significantly reduced.
In class B amplifier circuits, compared to class A circuits, the DC current can be reduced to almost zero, so there is less heat loss and the efficiency is good, but the drawback is that switching distortion occurs because the output amplifier elements alternately shift to the cut-off region. There is.

Therefore, in order to combine the advantages of both class A and class B amplifier circuits and eliminate the disadvantages of both, the circuit system shown in FIG. 1 is used. In the figure,
The input signal is voltage amplified by the voltage amplification stage 1 of the class A amplifier and becomes the base input of complementary transistors Q ₁ and Q ₂ of the driver stage 2. The emitter outputs of these driver transistors Q ₁ and Q ₂ become base drive signals for the complementary output transistors Q ₃ and Q ₄ of the class A power amplification stage 3, and these emitter outputs are passed through resistors R ₁ and R ₂ respectively. This circuit drives a load such as a speaker (not shown) with electric power, and circuits 1 to 3 operate as a class A power amplifier.

The circuit power supply ±B is used as the operating power supply for the driver stage 2 in this class A amplifier, and the DC voltage supply for the power amplification stage 3 is provided by the output transistors Q ₃ and Q ₄
This is done by a voltage source _E0 provided in a floating state between collector terminals a and b, which are _the power supply terminals of ing.

On the other hand, it includes a voltage amplification stage 4 which inputs the same signal as the input signal of the class A power amplifier, and a driver stage 5 including driver transistors Q ₅ and Q ₆ driven by the amplified output. Note that E ₁ and E ₂ between the bases of transistors Q ₅ and Q ₆ indicate a bias generation circuit. Furthermore, B is driven by the collector outputs of driver transistors Q ₅ and Q ₆ .
A class B power amplification stage 6 is provided, which includes a pair of transistors Q ₇ and Q ₈ that are complementary to each other and perform class B operation. Driver transistor _Q5 , _Q6
A diode is connected between each collector and the power supply ±B.
A series connection circuit of D ₁ and resistor R ₃ and diode D ₂ and resistor R ₄ is provided, and transistors Q ₅ ,
Each collector current of Q ₆ is connected to the output transistor Q ₇ , Q ₈
These collector output currents are transferred to A
The signal is supplied to collector terminals a and b of output transistors Q ₃ and Q ₄ of the class amplifier.
Note that resistors R ₅ and R ₆ represent emitter resistances of class B transistors Q ₇ and Q ₈ .

Here, assuming that transistor Q ₇ is on and transistor Q ₈ is off during a half cycle of the input signal, a current and voltage corresponding to the input signal level appear at the collector of transistor Q ₇ . This collector output is applied to the collector (a) of the class A transistor _Q3 , and a lower voltage level-shifted by _E0 of this output level is applied to the transistor
It will be applied to the collector (b) of _Q4 . Therefore, the currents of the transistors Q ₃ and Q ₄ and the current to the load (not shown) are supplied from the collector output of the class B amplifier Q ₇ , and there is a current between the collectors (a-b) of the transistors Q ₃ and Q ₄ . , a constant voltage E ₀ is always applied.

In the other half cycle of the input signal, contrary to the above, only class B transistor _Q8 is turned on,
Current and voltage according to the input level are supplied to the collector b of the class A transistor _Q4 , and the transistor
By supplying a voltage _E0 higher than that to the collector a of _Q3 , a circuit with high efficiency and no switching distortion is achieved. In addition, power supply
The midpoint voltage generated by resistors R ₇ and R ₈ of E ₀ is fed back to the voltage amplification stage 4 by resistors R ₉ and R ₁₀ .

In such a circuit, the voltage gains of both the class A and class B amplifiers must be set to be approximately equal, and the circuit has the disadvantage of becoming complicated and difficult to design. If the frequency and phase characteristics are not uniform, the output may be clipped, resulting in distortion. Furthermore, since both amplifiers operate independently when the power is turned on or when an excessive input is applied, the output transistor may become saturated and malfunction.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a highly efficient and distortion-free class A power amplifier circuit.

The class A power amplifier circuit according to the present invention has a current output that is controlled according to the difference between the midpoint voltage of a floating voltage source provided between the power supply terminals of the class A output amplifier element and the circuit output voltage. The current sources are respectively provided between the circuit power supply (±B) and the power supply terminals of the pair of amplifying elements, and the outputs of these current sources are supplied to the pair of complementary output amplifying elements that operate in class A. It is characterized by the fact that

The present invention will be explained below with reference to the drawings.

FIG. 2 is a circuit diagram of an embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals.
Voltage amplification stage 1, driver stage 2 and A of class A amplifier
Each configuration of class power amplification stage 3 is equivalent to that shown in Fig. 1,
Also, the first fact is that a floating voltage source E ₀ is provided between the collectors (a-b) of the A _- class output transistors Q ₃ and Q ₄ to determine the A-class bias current of the output transistors Q 3 and Q ₄ . This is similar to the example in the figure.

In order to detect the midpoint voltage of this floating voltage source E ₀ , a voltage dividing circuit having resistors R ₇ and R ₈ of equal value connected in series is provided between this voltage source E ₀ . still,
In this example, a voltage source E ₃ is provided between resistors R ₇ and R ₈ , which is connected to the comparison transistor described later.
Q ₉ and Q ₁₀ are further used as DC voltages for setting bias currents of current source transistors Q ₁₁ and Q ₁₂ . Voltages whose levels are shifted in the negative or positive direction by voltage E3/2 from the above midpoint voltage are applied to the emitters of NPN and PNP transistors Q ₉ and Q ₁₀ for level comparison through resistors R ₁₁ and R ₁₂ , respectively. has been
The amplifier output voltage is applied to both the bases of transistors Q ₉ and Q ₁₀ .

Current sources 7 and 8 of a current mirror type are provided, which receive the outputs from the transistors Q ₉ and Q ₁₀ as inputs. The current source 7 has a diode D ₃ whose input is the collector output of the transistor Q ₉ and an output transistor Q ₁₁ , and resistors R ₁₃ and R ₁₅ determine the current transfer ratio (current gain). The current gain is set to a large value to increase the current drive capability of the output transistor _Q11 . Similarly, the current source 8 is
It has a diode D ₄ whose input is the collector output of the PNP transistor Q ₁₀ and an NPN output transistor Q ₁₂ , and the resistors R ₁₄ and R ₁₆ determine the current gain, and this circuit 8 also controls the current drive of the output transistor Q ₁₂ . It is designed to increase its ability.

The collector output current of these output transistors is the collector terminal a of class A output transistors Q ₃ and Q ₄ ,
These current sources 7 and 8 are equivalently supplied to the circuit power supply ±B and the class A output transistor.
They are provided between collector terminals a and b of Q ₃ and Q ₄ , respectively.

In this configuration, when there is no signal, the output is at zero volts, and the DC bias current of class A transistors Q ₃ and Q ₄ is determined by the floating voltage E ₀ , so if this voltage E ₀ is selected to be small, the idle current can be reduced. can be made small. On the other hand, zero voltage is applied to the bases of the level comparison transistors Q ₉ and Q ₁₀ , and voltages obtained by shifting the midpoint voltage of voltage _E0 to the negative and positive by E3/2 are applied to each emitter, respectively. Therefore, an equal current corresponding to this voltage E3/2 flows through each transistor Q ₉ and Q ₁₀ , and this is transmitted to the transistors by current mirror circuits 7 and 8.
Transferred to Q ₁₁ and Q ₁₂ . This DC bias current output from transistor Q ₁₁ flows into transistor Q ₁₂ via resistors R ₇ and R ₈ . In this state, the midpoints of the circuit output voltage and the floating voltage E ₀ are both zero volts and are balanced.

When a signal is input and the base inputs of transistors Q ₃ and Q ₄ become a positive half cycle, the circuit output also swings to a positive level accordingly. This is because the A-class transistors Q ₃ and Q ₄ are of emitter follower output type. Therefore, since the base input of transistor _Q9 swings in the positive direction, the current of transistor _Q9 increases. Therefore, the current of transistor _Q11 also increases accordingly, making it a class A power transistor.
Collector current and voltage are supplied to Q ₃ according to the input level. Also in the negative half cycle, the collector of the transistor _Q4 is supplied with current and voltage according to the input from the transistor _Q12 .

At this time, transistors Q ₉ and Q ₁₀ are controlled according to the difference between the circuit output voltage and the midpoint voltage of the floating voltage E ₀ , so the circuit output voltage is always equal to the midpoint voltage of the floating voltage E ₀ . The conduction states of transistors Q ₁₁ and Q ₁₂ are controlled so as to achieve this. By doing this, the circuit operates so that the circuit output is at the midpoint of voltage E ₀ in any case, so saturation of the output transistor is prevented with a simpler configuration compared to the example in Figure 1, and signal distortion is reduced. Occurrence is prevented.

As described above, according to the present invention, with an extremely simple configuration, abnormal circuit operation can be prevented compared to a conventional circuit in which a class B amplifier circuit is separately provided as a power supply, and a highly efficient and high performance class A amplifier circuit can be realized. This is a power amplifier.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional high efficiency class A amplifier, and FIG. 2 is a circuit diagram of an embodiment of the present invention. Explanation of symbols of main parts, 3...Class A power amplifier stage, 7, 8...Current source, _Q3 , _Q4 ...Class A output power element, _Q9 , _Q10 ...Level comparison transistor, Q ₁₁ , Q ₁₂ ... Current source output transistor,
E ₀ ...Floating voltage source.

Claims (1)

[Claims] 1. Complementary positive side and negative side output amplification elements that perform class A operation, a floating voltage source provided between the power supply terminals of the positive side and negative side output amplification elements, and a voltage of the floating voltage source. a voltage dividing circuit connected between the terminals, a voltage comparing means for generating positive side and negative side comparative outputs according to the difference between the potential at the voltage dividing point of the voltage dividing circuit and the circuit output voltage; The positive side and negative side output currents are respectively controlled by the negative side comparison output, and the positive side and negative side output currents are provided between the circuit power supply and the power supply terminals of the positive side and negative side output amplification elements, respectively. a current source that supplies the positive side and negative side output amplification elements, respectively, and the voltage divider circuit includes a bias voltage source;
A pair of resistance elements are connected between the positive and negative terminals of the bias voltage source and the positive and negative terminals of the floating voltage source, and the voltage comparison means compares the potentials of the negative and positive terminals of the bias voltage source with the potentials of the floating voltage source. A characterized in that it consists of positive side and negative side transistors whose base-emitter potential is a potential difference with a circuit output voltage, and wherein collector currents of the positive side and negative side transistors are used as the positive side and negative side comparison outputs.
class power amplifier circuit.