Section IV Model 204B
Paragraphs 4-11 to 4-15
Figure 4-2. Simplified Schematic Diagram
4-11. The resistive voltage divider network consists CR6. This circuit samples the oscillator circuit out-
of R3 and Z1 which provide negative feedback voltage put, and supplies bias proportional to the output signal
to maintain the oscillator circuit output at a constant to control the dynamic resistance of the diodes in the
level. The negative feedback is developed in part due resistive voltage divider network.
to the dynamic resistance of CR4 and CR5 which is
controlled by the amount of forward bias applied to 4-15. Peak detector Q5 conducts only on the negative
the diodes by the peak detector circuit. If the oscil- peak of the output signal. At 7 volts peak, breakdown
lator circuit output changes, the peak detector detects diode CR6 breaks down and the voltage at the junction
the change and converts it to a new bias level for the of CR6 and C25 through C29 decreases. This changes
diodes. Diode conduction changes (seen as an imped- the bias to CR4 and CR5, which affects the resistance
ance change in the bridge), and results in a differing of these diodes. Capacitors C25 through C29 act to
amount of negative feedback, If the negative peak of averagethe bias voltage applied tothe diodes over the
the oscillator output signal exceeds -7 volts then, the period of one cycle.
peak detector circuit would decrease the forward bias
FREQUENCY
on CR4 and CR5, increasing diode dynamic resistance.
Increased impedance in Z1 of the divider increases
LAG
the amount of negative feedback to the emitter of the 0 A
amplifier. Increasing the negative feedback results
in a decrease in the net input tothe amplifier and thus
0.3
the output signal decreases. The oscillator output is
maintained at a constant 14 volts peak-to-peak. PHASE
F
0.2
4-12. Two amplifiers, Q1 and Q2, (figure 5-9) am-
plify the signal and apply it to complementary emitter
0
followers Q3 and Q4. The emitter followers are for-
LEAD
ward biased by CR2 and CR3 and under a no-signal
condition are conducting slightly to minimize cross-
over distortion. The oscillator circuit output is
R
sampled by the peak detector and also coupled to the
RATIO -
POSITIVE FEEDBACK
bridged-T attenuator.
TO AMPLIFIER PHASE
204 0-S -13A
4-13. PEAK DETECTOR. FEEDBACK TO RC NETWORK
4-14. The peak detector circuit consists of Q5 and Figure 4-3. RC Network Characteristics
4-2 01369-2 |