HP 70427A User Manual page 448

Table 13-5
25 Hz
R 681 k
1
R 26.1 k
2
1 μF
C
F 6.10 Hz
z
BW Gain, 0.054
Ratio
BW Gain, dB –25.4
dB
BW Gain, 0.038
Ratio
BW Gain, dB –28.3
dB
100 MHz Phase Locked Loop Integrator
53 Hz 126 Hz 300 Hz
316 k 121 k 42.2 k
26.1 k 23.7 k 21.5 k
0.2 μF
0.47μF 0.1μF
13.0 Hz 33.6 Hz 74.0 Hz
0.114 0.271 0.265
–18.7 –11.3 –3.81dB
dB dB
0.083 0.196 0.509
–21.7 –14.2 –5.86
dB dB dB
The integrator op-amp's negative input, which is at virtual ground, is
switched between the networks. All eight network inputs are in parallel and
must be driven by the phase detector amplifier. All eight feedback paths are
also in parallel and must be driven by the integrator op-amp. The component
values of R and R are such that only the integrator network selected by the
1 2
eight-input analog multiplexer used for switching may put a significant load
on either op-amp. Stability in the integrator op-amp is maintained by adding
the 10 pF capacitor between the op-amp's negative input and output. The 10
pF capacitor counteracts the excess phase shift added by the analog
multiplexer.
The integrator op-amp output is connected to the 100 MHz VCXO tuning
port select analog multiplexer. This multiplexer selects between connecting
the integrator to the VCXO and closing the loop, grounding the tune line
(100 MHz NO TUNE), or connecting the tune line to the CUST/INT tune
line (1 ppm/V).
The tuning port select analog multiplexer is connected to five locations. The
main output is the 100 MHz VCXO tune port. It is also connected to the
diagnostic multiplexer system, the integrator out-of-lock detector, the
search/acquisition circuit and an amplifier used for loop/VCXO noise
diagnostics. The noise diagnostic amplifier is not used in normal module
functions. The amplifier is an 80 dB AC coupled amplifier, connected to the
diagnostic multiplexer system. It is for monitoring the tune line noise of the
100 MHz PLL inside the loop bandwidth, under closed loop conditions.
100 MHz Reference Loop (A7A1)
650 Hz 1.53 3.63 kHz
kHz
17.8 k 9.09 k 3.83 k
21.5 k 23.7 k 23.7 k
0.047μ 0.015 6800 pF
μF
F
157 Hz 448 Hz 988 Hz
1.40 3.29 7.81
2.91 dB 10.3 dB 17.8 dB
1.21 2.61 6.19
1.64 dB 8.23 dB 15.8 dB
HP 70427A/HP 70428A User's Guide 13-13
Block Diagram
10.4
kHz
2.15 k
34.8k
1800 pF
2.54
kHz
22.4
27.0 dB
16.2
24.2 dB