JPS62606B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to push-pull amplifier circuits.

Conventional push-pull amplifier circuits are roughly classified into class A, class AB, and class B depending on bias conditions.

In class AB and class B push-pull amplifier circuits, the bias current is small, so the heat loss is small, but the input signal causes the output transistor to alternately become conductive and non-conductive, resulting in switching distortion.

Also, collector current I _C vs. base-emitter voltage V _BE in a transistor push-pull amplifier circuit.
Regarding crossover distortion caused by non-linearity in the rise of the characteristics (hereinafter referred to as I _C -V _BE characteristics), no matter how you set the bias conditions, the composite transfer characteristics will not be linear, and will not be linear in class A, AB It is known that cross-over distortion cannot be completely eliminated in both class and B-class cases. Cross-over distortion is particularly noticeable in the case of class B, which has low heat loss.

An object of the present invention is to provide a push-pull amplifier circuit that can reduce switching distortion and/or crossover distortion as described above in conventional push-pull amplifier circuits.

In order to achieve this object, the push-pull amplifier circuit according to the present invention includes bias correction means for applying a predetermined voltage via a rectifier between the bases of the first and second transistors connected in a push-pull manner and the output point; The device has means for applying a bias to each of the bases, and will be described in detail below in accordance with embodiments.

FIG. 1 shows an embodiment of the present invention, in which an NPN transistor Tr ₁ is a push-pull output transistor.
The emitters of the PNP transistors Tr2 and _Tr2 are commonly connected to the output point Q via emitter resistors _R1 and _R2 , respectively. A reference voltage source E ₁ for applying a base bias to the output transistors is connected between the bases of the output transistors Tr ₁ and Tr ₂ via resistors R ₃ and R ₄ , respectively.

Furthermore, a bias correction circuit ₁ consisting of a diode D ₁ and a reference voltage source E ₂ connected in series is provided between the base of the output transistor Tr 1 and the output point Q, and further between the base of the output transistor Tr ₂ and the output point Q. A bias correction circuit 2 consisting of a diode D ₂ and a reference voltage source E ₃ connected in series is provided.

Here, the cathode of diode _D1 is connected to the base of transistor _Tr1 , and the anode of diode _D2 is connected to the base of transistor _Tr2 .

In such a circuit configuration, the reference voltage source _E1 is set so as to apply a bias current of approximately class B to the output transistor when there is no input signal. At that time, a small current is passed through the diodes D ₁ and D ₂ , and the reference voltage sources E ₂ and E ₃ are set so that both the diodes D ₁ and D ₂ are in a conductive state close to a non-conductive state.

Now consider the operation of the output transistor _Tr1 according to FIG. For the positive half cycle of the input signal V _i , the load current flows from the power supply +B through the output transistor Tr ₁ and the emitter resistor R ₁ to the load R _L
flows to where the output transistors Tr ₁ and Tr ₂
Let the potentials of the bases P ₁ and P ₂ be V _P1 and V _P2 , and let the potential of the output point Q be V _Q , and
The potential of P ₁ and P ₂ , i.e. transistors Tr ₁ and Tr ₂
The bias voltages of V _QP1 and V QP2 are assumed to be V QP1 and V _QP2 .

Here, the bias V _QP1 is set as shown by the solid line A in Figure 2. Then, in the case of a positive half cycle of the input signal V _i , the bias V _QP1 increases, so the diode D ₁ becomes non-conductive, and the bias correction circuit 1
is disconnected, and in this case transistor Tr ₁ becomes conductive as in normal class B or AB operation. During the negative half cycle of the input signal V _i , the diode D ₁ is always conductive and the bias voltage V _Q
P1 is input signal V _i , load R _L resistor R ₃ and reference voltage source
Since it is a positive value determined by the value of E ₂ , Tr ₁ is in a conductive state. The forward voltage of the diode _D1 is also involved here, but since it changes depending on the value of the resistor _R3 , it is considered to be included in the resistor _R3 .

Note that the output resistance of the drive amplifier _A1 was set to be sufficiently smaller than the value of the resistor _R3 .

In this way, the output transistor _Tr1 is always in a conductive state for any input signal, so that switching distortion does not occur and the loss is almost the same as that of a class B amplifier. In this case, the bias voltage V _QP1 should always be V _QP1 > 0 as shown by the solid line A in Figure 2, so this is based on the reference voltage source E ₂ , the forward voltage V _FD1 of the diode D ₁ when there is no signal, and the resistor R This can be achieved by choosing the value of ₃ appropriately.

Also, the bias voltage V _QP1 of the transistor Tr ₁ when there is no signal is E ₂ -V _FD1 , so by setting E ₂ -V _FD1 small, the bias current when there is no signal can be reduced (that is, the heat loss can be reduced). I can do it.

Also, at this time, I _C −V _B of the output transistor Tr ₁
The solid line A in Figure 3 depicts the change in _{the E} characteristic.

Also, the dotted line B in Figures 2 and 3 shows the case where the resistor R ₃ is made smaller, and the smaller it is, the closer the bias voltage becomes to the I _C -V _BE characteristic of the output transistor Tr ₁ of a conventional class B amplifier. There is a portion where the transistor Tr ₁ is turned off, as shown in the shaded area D.

Similarly, the dotted line C shows the case where the resistance R ₃ is increased. It can be seen from FIG. 3 that the I _C -V _BE characteristic of the output transistor Tr ₁ can be freely set by appropriately selecting the values of E ₂ and resistor R ₃ .

In this case, for example, if the I _C -V _BE characteristic is selected to be close to a square-law characteristic, crossover distortion can be reduced as is well known.

The above explanation is the same for the output transistor Tr ₂ , so a detailed explanation will be omitted, but the value of the reference voltage source E ₃ , the forward voltage of the diode D ₂ when there is no input signal, and the value of the resistor R ₄ should be appropriately selected. As a result, the bias current can be reduced and conduction can be achieved for any input signal, and crossover distortion can be reduced by making the I _C -V _BE characteristic a square-law characteristic as described above. Also, if the adverse effects of switching distortion are not very large, the bias voltage V _QP
It is not necessary to always make ₁ greater than zero, and crossover distortion can be reduced simply by making the I _C -V _BE characteristic closer to the square characteristic.

From the above explanation, it can be seen that with the circuit configuration shown in FIG. 1, it is possible to achieve a push-pull amplifier with low bias current (that is, low heat loss), no switching distortion, and low crossover distortion.

Also, in the above explanation, the output transistor is a single-stage push-pull output, but multiple stages of push-pull output (for example, Darlington connection,
triple darlington connection, etc.) may also be used.

FIG. 4 shows a specific embodiment of the present invention, which is basically the same as the circuit shown in FIG. 1, and the same parts as in FIG. 1 are denoted by the same symbols. As the reference voltage source E ₁ in FIG. 1, a series circuit of resistors R ₁₄ , R ₁₅ , diodes D ₇ , D ₈ and resistors R ₁₆ , R ₁₇ was used. Associated with the resistors R ₁₄ and R ₁₇ are the output transistors Tr ₁ and
Provides base bias voltage for Tr ₂ . Also, as reference voltage sources E ₂ and E ₃ , resistors R ₇ , R ₈ , R ₉ , R ₁₀ ,
R ₁₃ , diodes D ₅ , D ₆ and transistors Tr ₅ , Tr ₆
By creating a voltage drop across the resistor R ₁₁ and the diode D ₃ through a constant current circuit consisting of the following, a reference voltage source E ₂ is obtained, and by creating a voltage drop across the resistor R ₁₂ and the diode D ₄ , the reference voltage source E Get ₃ . Also, the output transistors are transistors Tr ₃ and Tr ₄ , and emitter resistance.
Darlington is connected by adding R ₅ and R ₆ . Note that the diodes D ₇ and D ₈ are used to guarantee the temperature of the output transistor, and the diodes D ₃ and D ₄ are used to guarantee the temperature of the diodes D ₁ and D ₂ . Since the operation is the same as that shown in FIG. 1, the explanation will be omitted. In addition, in Fig. 1 and Fig. 4, diodes D ₁ and D ₂
Alternatively, a plurality of diodes connected in series or a resistor connected may be used.

FIG. 5 shows another specific embodiment according to the present invention, in which the diodes D ₁ and D ₂ of FIG. 4 are replaced with transistors Tr ₇ and Tr ₈ , respectively. Instead of transistors Tr ₇ and Tr ₈ , use a series connection of multiple transistors (for example, Darlington connection), or connect multiple diodes or resistors in series to the emitters of transistors Tr ₇ and Tr ₈ . You can also do it.

FIG. 6 shows an embodiment for further reducing crossover distortion, in which a plurality of bias correction circuits 11, 1 are connected between the base P ₁ of the output transistor Tr ₁ and the output point Q.
Furthermore, a plurality of bias correction circuits 12, 14 and 16 are connected between the base P ₂ of the output transistor Tr ₂ and the output point Q. The circuit shown in Fig. 6 maintains the advantages of the circuit shown in Fig. 1, but more finely corrects the non-linearity of the rise of the I _C -V _BE characteristic of the output transistor, and approaches the square characteristic as described above by cross-linking. This is intended to further reduce overdistortion.

Note that the series resistors R ₃₁ to _{R 36} in the bias correction circuits 11 to 16 are used for adjustment to bring the polygonal line approximation characteristics closer to a curved line. In the circuit of Fig. 6, the first
As in the circuit shown in the figure, first the output transistor Tr ₁
think about. Diode when there is no input signal
Reference voltage source E ₁₁ , so that only D ₁₅ becomes conductive
Explain E ₁₃ and E ₁₅ . Now E ₁₅ > E ₁₃ > E ₁₁ , as seen from the output point Q for one cycle of the input signal.
If we draw the potential V _QP1 at _one point P, it will look like E in Figure 7. At this time, reference voltage sources _{E 11 ,} E ₁₃ , E ₁₅ , resistors R ₃ ,
R ₃₁ , R ₃₃ , R ₃₅ and diode D ₁₅ when there is no input signal
Forward voltage V _FD15 is appropriately selected. Also, the changes in the I _C -V _BE characteristics of the output transistor Tr ₁ at this time are shown by the solid line H in FIG. 8, and the dotted lines in FIGS.
The characteristics are shown when transistors 12, 13, 14, 15, and 16 are removed and transistor Tr ₁ is operated in normal class B operation.

At this time, if the value of E ₁₅ -V _FD15 is set to a small value, the overall bias current can be reduced.

In this way, the reference voltage sources E ₁₁ , E ₁₃ , E ₁₅ , the resistors R ₃ ,
By appropriately selecting R ₃₁ , R ₃₃ , and R ₃₅ , the I _C -V _BE characteristic of transistor Tr ₁ can be more accurately approximated to the square characteristic by polygonal line approximation.
It is possible to further reduce the nonlinearity of the rise of the I _C -V _BE characteristic, which causes overdistortion. In the same way, the bias current of output transistor Tr ₂ is reduced, and it remains conductive for any input signal, making the I _C -V _BE characteristic more accurately close to the square-law characteristic and reducing crossover distortion. I can do it.

As described above, with the circuit configuration shown in FIG. 6, the bias current is small (that is, the heat loss is small), and switching distortion does not occur. Furthermore, a push-pull amplifier with less crossover distortion can be achieved. In the circuit configuration shown in FIG. 6, three bias correction circuits are used for one side of the push-pull output transistor, but it is clear that the number of bias correction circuits is not limited to three and that a large number of bias correction circuits can be used.

FIG. 9 shows yet another specific embodiment of the present invention, and the principle is the same as the circuit shown in FIG. 6. Diodes D ₁₁ , D ₁₂ , D ₁₃ , in the circuit in FIG.
Tr ₁₇ , Tr ₁₈ , Tr ₉ , Tr ₁₀ , instead of D ₁₄ , D ₁₅ , D ₁₆
Tr ₁₁ and Tr ₁₂ are used. Also, the reference voltage source E ₁₁ ,
Voltage drop due to diode D ₃ and resistor R ₁₁ instead of E ₁₃ , E ₁₅ , voltage drop across R ₂₃ , D ₃ and R ₁₁ , and
The voltage drops of R ₂₂ , R ₂₃ , D ₃ and R ₁₁ are used.
Similarly, D ₄ is applied to the reference voltage sources E ₁₄ , E ₁₆ , E ₁₈ .
and the voltage drop of R ₁₂ , the voltage drop of R ₂₄ , D ₄ , and R ₁₂ , and the voltage drop of R ₂₅ , R ₂₄ , D ₄ , and R ₁₂ are used.

In the above explanation, the case was mainly explained in which switching distortion does not occur even if a bias voltage corresponding to class AB or B class is applied, and crossover distortion is reduced, but the present invention is not limited to this. A
It is clear from the above explanation that it can be used to further reduce crossover distortion when applying a bias equivalent to that of a class operation.

Furthermore, the present invention can be operated in class B or class AB, in which case switching distortion cannot be eliminated, but crossover distortion can be reduced.

As explained above, according to the present invention, a push-pull amplifier circuit that can reduce switching distortion, crossover distortion, or both can be realized.

In the explanation so far, a bipolar transistor has been used as the output transistor, but it is clear that a field effect transistor can have the same effect.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
3 and 3 are diagrams for explaining the circuit operation of FIG. 1, FIG. 4 is a circuit diagram showing a specific embodiment according to the present invention, and FIG. 5 is a diagram showing another specific embodiment according to the present invention. 6 is a circuit diagram showing an embodiment of the present invention to further reduce crossover distortion, and FIGS. 7 and 8 are diagrams for explaining the operation of the circuit shown in FIG. 6. , FIG. 9 is a circuit diagram showing still another specific embodiment of the present invention. In the figure, Tr ₁ and Tr ₂ are transistors, D ₁ , D ₂ , D ₁₁
~ _D16 are diodes, _E1 ~ _E3 , _E11 ~ _E16 are reference voltage sources, and R _L is a load resistance.

Claims (1)

[Claims] 1. In a push-pull amplifier circuit consisting of a first and a second transistor whose emitters are each connected to a common output point, a first direct current connected in parallel between the base of the first transistor and the common output point. a first bias circuit comprising a power supply and a first rectifying element and forward biasing between the base and emitter of the first transistor;
a second bias circuit that forward biases between the base and emitter of the second transistor, the second bias circuit comprising a second DC power supply and a second rectifying element connected in parallel between the base of the transistor and the common output point; and first and second resistors whose one ends are respectively connected to the bases of the first and second transistors, and between the other end of the first resistor and the other end of the second resistor. a third DC power supply that is connected to and biases the first and second transistors to class B or class AB; and a third DC power supply that is connected to the bases of the first and second transistors via the first and second resistors. A push-pull amplifier circuit comprising: a drive stage amplifier to which a common input signal is applied, and the output impedance of the drive stage amplifier is made sufficiently smaller than the resistance values of the first and second resistors.