TB2110FN
○ Phase comparator
The phase comparator compares the phase difference between the reference frequency signal fed from the
reference frequency divider and the divided output from the programmable counter, and outputs the difference.
In this way it controls the VCO through a low-pass filter to ensure that the frequencies and the phases of these
two signals are matched to each other.
Because this phase comparator has two tri-state buffers DO1 and DO2 connected in parallel as its outputs, you
can design the optimum filter constant for each of the FM and AM bands.
Furthermore, you can use the DOHZ bit of register D2 to place the DO2 output in a high-impedance state as
necessary.
Shown above is a DO output timing chart and a typical active low-pass filter circuit based on a darlington
connection of FET and bipolar transistors.
The filter circuit shown above is just one example. When designing the actual circuit, consider the band
configuration and the desired characteristics of your system.
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2002-10-30