A13 Limiter/Amplifier Assembly; A14 Limiter/Amplifier/Mixer Assembly - HP 5340A Operating And Service Manual

4-186. A13 LIMITER/AMPLIFIER ASSEMBLY, 05340-60010

4-187. Figure 8-19 shows the schematic diagram for A13. The Limiter/Amplifier input receives
the 20 MHz output of Preamplifier No.
automatic amplitude discrimination.
each containing a current source. Limiting action is due to current limiting in the IC. R4, R6, R8,
and R9 set the operating bias for the constant current source in U1A. L4 provides high frequency
peaking. The circuitry for UlB, U2A, and U2B is similar to U1A.

4-188. A14 LIMITER/AMPLIFIER/MIXER ASSEMBLY, 05340-6001 1

4-189. The inputs to A14 (Figure 8-20) are the preamplifier No. 2 signal and the 20 MHz reference
signal. The output provided by A14 is Fn, where F n
VCO No. 1 frequency that provides the required 20 MHz IF. The signal output of Preamplifier
No. 2 is the result of mixing the harmonics of F2 with the counter input signal Fx.
4-190. Operational amplifier U1 provides approximately 46 dB of gain for the preamplifier
signal. U1 operates open loop to provide maximum gain. L5, C10, L6, and C12 are decoupling
networks. L7 and C13 give bandpass filtering at 20 MHz. Q1 and Q2 form a differential
amplifier to provide two signals out of phase to drive the mixer (CRl-4). Q3 amplifies the 20
input signals which is in range of 20 kHz to 3 MHz. The demodulator output connects to low pass
filter L8, C19, and C20. The filter rolloff point is approximately 3 MHz. Comparator U2 has a
10% hysteresis to discriminate against noise that could give a false indication of zero crossover.
The input to U2 is approximately 1 volt p-p and the
the counter circuits.
4-191 A15 10 MHz DOUBLER ASSEMBLY, 05340-60012
4-192. The 10 MHz Doubler (Figure 8-21) receives a 10 MHz reference from A19, doubles the
reference frequency to 20 MHz, and supplies two outputs. One of the 20 MHz outputs is used by
Phase Detector A4 and the other is routed to the Limiter Amplifier/Mixer A14.
4-193. The
10 MHz reference couples through
and C3. The tank circuit helps to filter out noise on the reference signal. Diode CR1 couples the
positive half cycle of the 10 MHz signal to UlA(1) and CR2 couples the negative half cycle to
half cycle of the
develops a negative going half cycle
increases conduction and a constant current source supplies the emitters of the differential
amplifier, then the right half of the differential amplifier will decrease conduction. This develops
a positive going half cycle of UlA(11). When CR2 conducts, the right half of the differential
amplifier again decreases conduction and the left half increases conduction. The net result is a
full wave rectified signal of 20 MHz at UlA(12) and UlA(11). C7 and C8 couple the 20 MHz
signals to U1B. The operation of U1B is similar to U1A. The signal out of the left half of U1B is
developed across a 20 MHz tank circuit and coupled through C15 to A14. In a like manner, the
output of the right half of U1B is coupled to A4. Rl-C5, Rll-C9, and L2-C6 serve as filters for
the power supply voltages.
voltage specification for U1.
4-194. A17A1 DIRECT COUNT AMPLIFIER ASSEMBLY, 05340-60038
4-195. This assembly (Figuke 8-23)
The input signal a t A17J1, is received from the sampler via A2FL1. The output, which is digital
(EECL levels), is routed tb/A22 for counting. The input is ac coupled through C1 and C2. The
series capacitor arrangelrient allows polarized capacitors to be used to couple ac.
at pin 10 and provides the necessary limiting action for
1
20 kHz N. N is the harmonic multiplier of
=
a current source. When the positive
at UlA(12).
Since the left half of the differential amplifier
is a wide band analog amplifier with automatic gain control.
Model 5340A
Theory of Operation
4-43