New Class A power amplifier circuit@has been issued - voice phone

The so-called "New Class A" refers to the use of the "synchronous bias principle" to allow the base voltage of the output stage transistor
to float with the size of the signal, so that the transistor does not have a cut-off process during operation.
    Figure 2-15 is the new Class A The working principle diagram of the analog power amplifier circuit. As can be seen from the figure, the basic structure of this circuit is
the same as the usual fully symmetrical complementary OCL circuit. The difference is its synchronous bias circuit. The basic structure will be introduced first,
and then the synchronization will be introduced. The working principle of the bias circuit.
    VTr and VT2 form the differential input stage of PNP polarity, the field effect transistor VTs is its constant current source , VT3 and VT4
form the differential stage of NPN polarity, and VT6 is its constant current source. The two sets of differential input groups are symmetrically complementary. This circuit uses a field
effect transistor as the constant current source of the differential circuit. Compared with the transistor constant current source, the field effect transistor constant current source has a simple circuit,
does not require bias, and has good temperature stability. and other characteristics. The dynamic internal resistance of the field effect transistor constant current source is as high as several megaohms, which is very close to
the ideal constant current source, while the dynamic internal resistance of the transistor is only tens to hundreds of kiloohms. Use field effect transistors for constant current The common mode rejection ratio of the differential amplifier of the source
is one or two orders of magnitude higher than that of the differential circuit using a transistor constant current source. Many advanced power amplifier
circuits use field effect transistors as the input stage of the differential circuit of the constant current source .
    Input signal The coupling capacitors cl and Ri are input from the base of VTi-VT3, and negative feedback is added to
the bases of VT2 and VI4. After the input signal is amplified by complementary differential push-pull, the collector output of VTi.VT3 is input voltage
amplified The stage VT8.1n1 is used for single-ended push-pull amplification. The amplified signal is then
amplified by the emitter output device VTio and VTii for the second stage voltage, and then drives the composite complementary push-pull output stage composed of VT14~VT17 for power output.
    The synchronous bias circuit composed of VTg, VTi, VT13, RP1, RP2 and VD1~VD4 is
the core part of the new Class A power amplifier, which will be analyzed in detail below.
    Since the bias circuit has a constant voltage function, a stable voltage can be obtained by adjusting the bias resistor. Therefore, by
adjusting RPi and base)2, you can "provide the required bias voltage to the output circuit, so that the output tube outputs a static current that can prevent the
output signal from being distorted. Adjusting base, VTg, etc. can make The bias circuit of VTio and V
provides the bias voltage y B1 required for Class A working conditions. In this circuit, it is 4,1 Vo. Adjusting RP;
Provides the required bias voltage V B3 - V B3, which is approximately 1.45V.