____________________________________________________________________________ Amplifiers
the input signal, although they will be equal to each other in amplitude. If the output
signals must be larger in amplitude than the input signal, use a circuit such as the one
shown in Figure 5-27.
Figure 5-27. Two-stage Transistor Phase Splitter
5-88. Figure 5-27 also shows a two-stage phase splitter. C1 couples the input signal to
the base of Q1. R1 develops the input signal and provides bias for the base of Q1. R2
provides bias and temperature stability for Q1. C2 decouples signals from the emitter of
Q1. R3 develops the output signal of Q1. Since Q1 is configured as a CE amplifier, the
output signal of Q1 is 180 out of phase with the input signal and larger in amplitude. C3
couples this output signal to the next stage through R4. R4 allows only a small portion of
this output signal to be applied to the base of Q2. R5 develops the input signal and
provides bias for the base of Q2. R6 is used for bias and temperature stability for Q2. C4
decouples signals from the emitter of Q2. R7 develops the output signal from Q2. Q2 is
configured as a CE amplifier, so the output signal is 180 out of phase with the input signal
to Q2 (output signal from Q1). The input signal to Q2 is 180 out of phase with the original
input signal, so the output from Q2 is in phase with the original input signal. C5 couples
this output signal to the next stage. So the circuitry shown provides two output signals that
are 180 out of phase with each other. The output signals are equal in amplitude with each
other but larger than the input signal.
PUSH-PULL AMPLIFIERS
5-89. One use of phase splitters is to provide input signals to a single-stage amplifier that
uses two transistors. These transistors are configured so that the output signals will add
together. This allows more gain (usually power gain) than one transistor could supply by
itself. This circuit is usually used as a power amplifier and is known as a push-pull
amplifier.
5-90. Figure 5-28 shows the circuit of a transistor push-pull amplifier. The phase splitter
for this amplifier is the transformer T1. However, any one of the phase splitters shown
earlier in the chapter could be used.
23 June 2005
TC 9-62
5-25
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