Rev. 1.0, 02/00, page 637 of 1141
26.7.6
Phase Comparison
The phase comparison circuit measures the difference of time between the reference signal and the
comparing signal with a digital counter. REF30 signal is used for the reference signal, and HSW
signal (VideoFF) or NHSW signal (NarrowFF) from the HSW timing generator is used for the
comparing signal. In record mode, however, the phase of REF30 signal is the same as that of the
vertical sync signal (Vsync) because the reference signal generator (REF30 generator) is reset by
the vertical sync signal (Vsync) in the video signals.
The error detection counter latches data at the rising or falling edge of HSW signal. The digital
filter circuit performs computation using this data as 20-bit phase error data. After processing and
adding the phase error data and the speed error data from the drum speed control system, the
digital filter circuit sends the data as the error data of the drum system to the PWM modulation
circuit.