JPS5836843B2 - Single-ended push-pull power amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PNP in a single-ended push-pull power amplifier circuit (hereinafter referred to as SEPP power amplifier circuit).
The present invention relates to a SEPP power amplifier circuit that can suppress the occurrence of distortion caused by the difference in characteristics between an l-transistor and an NPN transistor.

SEPP power amplifier circuits can be driven directly without using an output transformer and are widely used in high-fidelity amplifiers, and in recent years this circuit has been integrated into semiconductor integrated circuits.

FIG. 1 is a diagram showing a circuit generally proposed as such a SEPP power amplifier circuit, in which 1 and 2 indicate the upper N
3 and 4 are Darlington connection transistors forming a lower PNP transistor; 5 is a pre-driver transistor; 6 is an emitter resistance of transistor 5; 7 is a Darlington connection transistor forming a PN transistor;
is an input signal source, 8 is a transistor connected as a load of transistor 5, 9 is a transistor that forms a current mirror circuit together with transistor 8, 10 is an input current source for the current mirror circuit, 11 is a bias diode source, and 12 is a direct current a power supply terminal, and 13 is an output load.

In the conventional SEPP power amplifier circuit having the above configuration, the PNP transistor 8 is connected as the collector load of the pre-driver transistor 5, and the circuit structure is simply that a load resistor is connected to the collector of the pre-driver transistor 5. Compared to the case where
Are the current amplification factors of transistors 1 and 2 forming the N transistor different from those of transistors 3 and 4 forming the lower PNP l-transistor? Upper N
A difference occurs between the impedance ZRI seen from the collector of the transistor 5 when the PNP} transistor is conductive and the impedance ZR2 seen from the collector of the transistor 5 when the lower PNP transistor is conductive.

That is, the impedances ZRt and Z2 are expressed by the following equations, where the resistance value of the load 13 is RL, and the current amplification factors of the transistors 1 to 4 are hFE1 to hFFA, respectively.

ZR1-RLxhFE1xh hole,・・・・・・・・・
...(1) ZR2 = RL xhFE3Xh
pg4...---(2) As is clear from this equation, the impedance seen from the collector of transistor 5 is expressed as the product of the load resistance value and the current amplification factors of the upper and lower transistors, so If the current amplification factors of the upper and lower transistors are different, a difference occurs between ZRI and ZR2.

By the way, the difference between ZR1 and ZR2 causes the inconvenience that the voltage amplification factor of the predrive circuit differs depending on the positive or negative input signal, and the signal waveform at both ends of the load 13 becomes a distorted waveform as shown by the solid line in FIG. Put it away.

To eliminate such inconvenience, hFE1 to hFE
Between 4 }IFEt = }IFEs and hFE
All we have to do is establish the relationship 2 = h flower, but
Transistors 1 and 3 have different polarities, and it is extremely difficult to match their current amplification factors, especially when they are integrated into a semiconductor circuit.

The present invention was made in view of the above-mentioned disadvantages in conventional SEPP power amplifier circuits, and even if there is a difference in current amplification factors between the upper transistor and the lower transistor, this difference causes distortion in the output signal. S without
The present invention provides an EPP power amplification circuit.

EMBODIMENT OF THE INVENTION Below, the SEPP power amplifier circuit of this invention will be explained in detail based on an Example with reference to drawings.

FIG. 3 is a diagram showing an embodiment of the SEPP power amplifier circuit of the present invention. As shown in the figure, the predriver transistor 5 is a PNP transistor forming a current mirror circuit.
A structure is adopted in which a resistor 14 is connected in parallel with the collector-emitter circuit of the transistor 8 connected to the collector circuit of the transistor 8, and the structure is the same as the conventional structure except for this part. The same elements are given the same numbers as in FIG.

In the SEPP power amplifier circuit of the present invention having the above configuration, the gain G of the predriver transistor 5 is approximately R, assuming that the value of the resistor 6 is R6 and the value of the resistor 14 is R14.
It is expressed as 14/R6.

However, the value of the resistor 13 is R14<ZRI, R14<Z
The value is selected so that the relationship of R2 can be obtained.

Incidentally, the resistance value RL of the load 13 is often selected to be in the range of 4 to 16Ω, especially 8Ω, and the current amplification factor of the integrated NPN transistor, that is, hFB4, hFE2, hFB4, The value of is about 50 to 250, and on the other hand, the value of the current amplification factor of the PNP transistor, that is, h FE s is about 5 to 70.

Therefore, the value of the resistor 14 is determined taking these values into consideration.

By the way, in the present invention, for example, the current amplification factor of the NPN transistor is 1501, the current amplification factor of the PNP transistor is 30, RL is 8Ω, the emitter resistor 6 is 100Ω,
Assuming that the resistor 14 is selected to be 5KΩ, the gain Gu of the pre-driver transistor 5 when the upper transistor is conductive and the gain GL of the pre-driver transistor 5 when the lower transistor is conductive are expressed as follows. Become something.

However, ROU is the parallel combined resistance of ZRt and R14. However, R
OL is a parallel combined resistance of ZR,2 and R14. By the way, when ZRt and ZR2 are obtained by substituting the above specific values into equations (1) and (2), the following values are obtained.

Also, ROU ROL is R14 of 5KΩ, becomes.

Therefore, GU and GL shown in equations (3) and (4) are respectively 4.9 K/1. 0 0,
4.4 Expressed as K/100, resistors R6 and R1
The ratio of 4 is approximately 5K/100.

That is, the voltage gain of the predriver circuit of the circuit shown in FIG. 3 is hardly affected by the difference in current amplification factors of the transistors, and is almost determined by the values of the resistors 6 and 14.

In a conventional circuit without such a resistor 14, the voltage gains are ZR1/R6, ZR, and 2/R6, respectively, so if the circuit constants are selected to the same values as above, ZR1/R6 becomes Z
The value is approximately 5 times that of R2/R6, resulting in a difference of approximately 14 db between the two, resulting in distortion, but according to the present invention, as described above, the difference between GU and GL is extremely small. As a result, the signal waveform at both ends of the load becomes a distortion-free waveform, as shown by the dotted line in FIG.

FIG. 4 is a circuit diagram showing another embodiment of the present invention, in which a resistor 15 is connected between the emitter common connection point of transistors 8 and 9 and the power supply terminal 12, and the collector of transistor 1 is connected between the emitters of transistors 8 and 9 and the power terminal 12. It is connected to the emitter common connection point, and this point and the output generation point are connected in an alternating current manner.

Even with this structure, the effect of approximating the voltage gain to the ratio R14/R6 of the resistors 6 and 14 can be achieved, similar to the circuit shown in FIG.

By the way, in such a configuration, capacitor 1
Since the output signal generation point and the emitter of the transistor 9 are AC-coupled via the terminal 6, the emitter potential of the transistor 9 is higher than the potential of the terminal 12, and therefore,
Compared to the circuit shown in FIG. 2, a larger output can be taken out to both ends of the load.

As is clear from the above description, the SEPP power amplifier circuit of the present invention has the disadvantage that even if the current amplification factors differ due to the different polarities of the transistors forming the output stage, the output signal waveform is distorted due to this. Therefore, it can be said that it is a particularly useful circuit for converting circuits into semiconductor integrated circuits.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional SEPP power amplifier circuit, FIG. 2 is a diagram showing output signal waveforms, and FIGS. 3 and 4 are diagrams showing each embodiment of the SEPP power amplifier circuit of the present invention. 1, 2... Transistor for upper NPN transistor configuration, 3, 4... Transistor for lower NPN transistor configuration, 5... Predriver transistor, 6... ...Emitsuta resistance, 7...
... Input signal source, 8, 9 ... Current mirror circuit forming transistor, 10 ... Current source,
11... Bias diode, 12...
...Power terminal, 13...Load, 14...
・Gain setting/distortion correction resistor, 15... Resistor, 1
6... Capacitor.

Claims (1)

[Claims] 1. An NPNI transistor for forming a pre-driver stage, to which a signal is applied to the base and whose emitter is grounded via a first resistor, is connected to a current mirror circuit to which an input current is supplied from a constant current source. As a load, its collector is commonly connected to the collector of the transistor for forming the current mirror circuit, and a second resistor is connected between the common connection point of both collectors and the power supply terminal, and the second resistor The value of is the gain GU (=RoU/ya) when the upper transistor is conductive.
, gain GL when the lower transistor is conductive (-Roi/
Ra ) is GU″=GL″−. R14/R, (R6...First resistor (74, R14...
...Second resistance value ROTJ = ZRI / R1
4 (ZRt ""...Input impedance seen from the collector of the pre-driver transistor when the upper transistor is conductive) ROL-ZR, 2 / R14 (ZR2 """ Input impedance seen from the collector of the pre-driver transistor when the lower transistor is conductive) ] A single-ended push-pull power amplifier circuit characterized in that the value is selected to satisfy .