Phase Frequency Detector @ and Preamplifier @

The Phase/Frequency Detector outputs pulses whose width is proportional to the phase difference of the two input signals. These pulses are filtered by the combination of R24/C5 and R25/C6. The Preamplifier amplifies these pulses which are representative of the phase difference of the two input signals. Typical voltage levels for the Preamplifier are shown in Table 2.

Table 2. Typical Preamplifier Voltage Levels

Voltage Levels

1

Phase LockedT No Input At

Jl J2 J3

Ql

Emitter - 0 . 2 -1.c -1.0 -1.t

Base- 0 . 8 - 0 . 8 - 0 . 8 - 1 . 6

Collector - 5 . 2 -7.9-7.9 -1.9

Q2

Emitter - 0 . 2 -1.0 -1.0 -1.0

Base- 0 . 8 -1.7 -1.6 -0.8

1 Collector - 5 . 2 -1.8 -1.9 -7.9

Phase Lock Indicator @I

The outputs of the Preamplifier are compared to a reference voltage of -4 V by U2A and U2B. The output (HULM) is high ( act ive state) when the loop is unlocked.

This can be checked by disconnecting the 400 MHz input at A7A3Jl (96 cable) and measuring the output of U2 (Pl-26). With the loop unlocked (400 MHz removed), this voltage should be approximately 4.64 V.

6A7A3