3.5
Automatic functions
3 – 11
if necessary).
If the frequency is valid for the current range, then the reference
oscillator is temporarily halted, and the PLL tuning filter is “pre-
charged” to the correct voltage for the desired frequency.
The final step in the process is to arm a comparator that waits for
the next positive zero-crossing of the external frequency reference.
When that comparator fires, the VCO oscillator is un-haulted, and
the oscillation begins (approximately) in-phase with the external ref-
erence.
SR124
Analog Lock-In Amplifier
