JAMES D. MEINDL 
1173 
I.5K 
50^ 
XDUCER 
BASIC 
OSCILLATOR 
OUTPUT 
LOCAL 
OSC 
OUTPUT 
AGC 
INPUT 
6 MHz OSCILLATOR 
Figure 4. — Schematic diagram of CW exciter-oscillator circuit. 
40 dB. Figure 7 is a photomicrograph of the 
70 X 90 mil receiver chip. 
Audio Amplifier-FM Transmitter Circuit 
The schematic diagram of the audio amplifier- 
FM transmitter circuit is illustrated in Figure 
8. The active transistors in the audio amplifier 
are Q3, Q4 and Qg; the active transistor in the 
transmitter is Qg. The audio amplifier design 
makes very free use of the unique features of 
monolithic technology. The large open loop gain 
(~600) of Q3, Q4 and Qg is achieved by using 
high dynamic impedance monolithic lateral PNP 
transistors (Qr, and Qg) as load resistors op- 
erating at very low dc voltage drops compared 
with equivalent conventional resistors. The 
"push-pull" connection of Q3, Q4, Qr, and Qr, re- 
sults in no loss of gain in the transition from a 
differential first stage to a single ended second 
stage. Di and D2 are low forward voltage Al-Si 
Schottky diodes which serve to establish a suit- 
able collector voltage for Qo while conserving 
supply voltage as much as possible. To avoid 
oscillation in the audio amplifier it is internally 
compensated by C2 which as a Miller capaci- 
tance is effectively multiplied by the voltage gain 
of the second audio stage. Overall negative feed- 
back (R2) is used to set the closed loop gain of 
the amplifier. Symmetrical limiting is provided 
by including Schottky diodes D3 and D4 in the 
feedback path. The transmitter is a Colpitts 
oscillator in the common collector configuration 
(Qg) to minimize monolithic parasitic effects 
at 100 MHz; Dr, is the frequency modulating 
capacitance. 
The audio amplifier-transmitter circuit func- 
tions at supply voltages as low as 1.0 v. The 
amplifier gain is 35 dB, the bandwidth 20 kHz 
and the effective output voltage swing 0.8 v p-p. 
The transmitter frequency range is 88-108 
MHz. The total current drain of both circuits 
is 1.5 mA. Figure 9 is a photomicrograph of the 
70 X 90 mil audio-amplifier-FM transmitter 
chip ; in addition to it, three discrete components 
are used to implement the circuit. 
