JPH036022Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field The present invention relates to a low frequency amplifier circuit suitable for reducing crossover distortion and switching distortion that occur when switching output stage power transistors in a push-pull circuit. (b) Conventional technology Figure 1 shows a conventional low frequency amplification circuit. The circuit shown in FIG. 1 is constructed between power supplies +Vcc and -Vcc, and 1 is an input terminal to which an input signal is applied, and 4 and 5 are diodes that prevent the input signal from flowing backward. 2 is a current source connected between the power supply +Vcc and the anode of the diode 4; 3;
is a current source connected between the cathode of the diode 5 and the power supply -Vcc. Reference numeral 6 designates an input stage transistor, whose base is connected to the anode of the diode 4, whose collector is connected to the power supply +Vcc via a load resistor 8, and whose emitter is grounded via an emitter resistor 12. It is assumed that when the input terminal 1 is in a balanced state with no input, the input stage transistor 6 is driven only by the current source 2. Reference numeral 7 designates an input stage transistor that operates complementary to the input stage transistor 6, the base of which is connected to the cathode of the diode 5, and the collector connected to the power supply -Vcc through a load resistor 9.
and its emitter is grounded via an emitter resistor 13. It is assumed that, like the input stage transistor 6 , the input stage transistor 7 is driven only by the current source 3 when the input terminal 1 is in a non-input state. Reference numeral 14 denotes an output stage transistor, the base of which is connected to the collector of the input stage transistor 6 , the emitter connected to the power supply +Vcc, and the collector grounded via the current limiting resistor 10 and the emitter resistor 12. Reference numeral 15 denotes an output stage transistor that operates complementary to the output stage transistor 14 , the base is connected to the collector of the input stage transistor 7 , the emitter is connected to the power supply -Vcc, and the collector is connected to the current limiting resistor 11 and the aforementioned It is grounded via an emitter resistor 13. Reference numeral 16 denotes an output terminal, which is connected to the collectors (connection points) of the output stage transistors 14 and 15 . The circuit shown in FIG. 1 operates by connecting a load (not shown) such as a speaker to the output terminal 16. In a balanced state, the output stage transistors 14 ,
An idling current Iidl flows through the output path of No. 15,
When the input signal changes, the output stage transistor 14
The collector current flows into the load through the output terminal 16, or the current of the load flows into the collector of the output stage transistor 15 through the output terminal 16, thereby driving the load. Here, in the conventional technology, the base-emitter voltage of the output stage transistor 14 is V _BE , the current amplification factor of the output stage transistor 14 is h _FE , the resistance value of the load resistor 8 is R _S , and the input stage transistor 6 is When the collector current is _I0 , the idling current flowing through the output path of the output stage transistors 14 and 15 is
Iidl is expressed as Iidl=(I ₀ =V _BE /R _S )h _FE . However, since the idling current Iidl shown in the formula includes the term of the resistance value R _S , the idling current Iidl changes according to temperature changes without being temperature compensated. There was a problem in that crossover distortion and switching distortion in the signal appearing at the output terminal 16 became large. (c) Purpose of the present invention The purpose of the present invention is to reduce crossover distortion and switching distortion occurring in the output of a low frequency amplifier circuit. (d) Embodiment of the present invention Figure 2 shows the low frequency amplification circuit of the present invention.
Elements that are the same as those in the figure are given the same reference numerals. In FIG. 2, 20 and 24 are input stage transistors constituting the first push-pull circuit,
The bases of the input stage transistors 20 and 24 are commonly connected to the bases of the input stage transistors 6 and 7 , respectively.
The emitters of No. 4 are connected via a resistor 25. Reference numeral 17 denotes a first current mirror circuit consisting of transistors 18 and 19 whose bases are commonly connected, and the emitter of the diode-connected transistor 18 is connected to the power supply +Vcc (first power supply).
The transistor 19 has an emitter connected to the power supply +Vcc and a collector connected to the collector of the input stage transistor 6. 21 is a second current mirror circuit consisting of transistors 22 and 23 whose bases are commonly connected; in the diode-connected transistor 22, the collector is connected to the collector of the input stage transistor 24, and the emitter is grounded. (second power supply), and the collector of the transistor 23 is connected to the collector of the input stage transistor 7 , and the emitter is grounded. The input stage transistors 6 and 7 constitute a second push-pull circuit, and the output stage transistors 14 and 15 constitute a third push-pull circuit. A push-pull circuit has a parallel connection between the current +Vcc and ground. In FIG. 2, when the input signal level applied to input terminal 1 changes, the increase (decrease) in the collector current of input stage transistor 20 is equal to the increase (decrease) in the collector current of transistor 19. , the collector current of the output stage transistor 14 flows in accordance with the increase (decrease) in the collector current of the transistor 19. Similarly, the decrease (increase) in the collector current of the input stage transistor 24 and the decrease (increase) in the collector current of the transistor 23 are also equal.
A collector current also flows to the output stage transistor 15 in accordance with the decrease (increase) in the collector current of No. 3. As a result, by the complementary operation of the third push-pull circuit in the circuit of FIG.
A load (not shown) connected to 6 and 26 will be driven. Here, the collector current of the input stage transistor 20 is I ₀ and the collector current of the input stage transistor 6 is
I', Iidl is the idling current flowing through the emitter-collector path of the output stage transistor 14 , and _hFE is the current amplification factor of the output stage transistor 14 , then Iidl=(I ₀ −I') h _FE . That is, when the circuit of FIG. 2 undergoes a temperature change, if the collector current _I0 of the output stage transistor 20 changes by ΔI, the collector current I' of the input stage transistor 6 will also change by ΔI. Therefore, even if there is a temperature change, the idling current Iidl is Iidl={(I ₀ +ΔI)−(I′+ΔI)}h _FE =(I ₀ −I′)h _FE , which is the same as the formula. The same applies to the idling current flowing through the output stage transistor 15. That is, the idling current Iidl remains constant even if the temperature changes. As a result, the idling current Iidl is temperature compensated, and switching distortion and crossover distortion of the signals obtained from the output terminals 16 and 26 are reduced. In addition, when integrating the circuit shown in Figure 2 inside an IC,
Since each transistor is made on the same chip,
It is possible to make the input stage transistors 20, 6 , 24, and 7 have the same characteristics, which is also effective for IC implementation. (e) Effects of the present invention According to the present invention, since the idling current in the output stage of the low frequency amplifier circuit is temperature compensated, it is possible to reduce crossover distortion and switching distortion in the push-pull circuit of the output stage. is obtained.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional low frequency amplifier circuit.
FIG. 2 is a circuit diagram showing the low frequency amplification circuit of the present invention. 6 , 7 , 20, 22...input stage transistor,
14, 15 ... Output stage transistor, 17 , 21
...Current mirror circuit.

Claims (1)

[Scope of utility model registration request] first, second, and third push-pull circuits connected in parallel between a first power source and a second power source; and between the first power source and one transistor of the first and second push-pull circuits. a first current mirror circuit connected to the second power supply and the first current mirror circuit;
and a second current mirror circuit connected between the input of one transistor of the first push-pull circuit and the other transistor of the second push-pull circuit. , the output of one transistor of the second push-pull circuit is connected to the input of one transistor of the third push-pull circuit, and the output of the other transistor of the first push-pull circuit is connected to the input of the transistor of the first push-pull circuit. connecting the input to the input of the other transistor of the second push-pull circuit, and connecting the output of the other transistor of the second push-pull circuit to the input of the other transistor of the third push-pull circuit; A low frequency amplifier circuit characterized in that the idling current flowing through the output path of the third push-pull circuit is temperature compensated.