TC9256, 57APG/AFG

2006-07-14

19

Phase Comparator

The phase comparator outputs the phase error after comparing the phase difference of the reference

frequency signal supplied by the reference counter and the divided output from the programmable counter. The

frequencies and phase differences of these two signals are then equalized by passing them through low-pass

filters. These signals then control the VCOs.

The filter constants can be customized for FM and AM bands since the signals are output in parallel from the

phase comparator then pass through the two tristate buffer pins, DO1 and DO2.

The figures above show the DO output timing chart and a typical active low-pass filter circuit featuring a

Darlington connection between the FET and transistor.

The filter circuit shown above is just one example. Actual circuits should be designed based on the band

composition and the properties desired from the system.

Note:

On the TC9256APG and TC9256AFG, pin DO2 can be switched for use as pin OT-4.

Figure 8 DO Output Timing

Chart

Figure 9

Typical Active Low-Pass

Filter Circuit

Figure 7