PURPOSE:To release the operating speed of a discriminating device to 1/2 by using number of code violations in a specific time to switch the phase of a discriminating clock so as to discriminate the front and rear bits of a biphase code by two discriminating devices independently. CONSTITUTION:The front bit and the rear bit of a biphase code discriminated and recovered by the discriminating devices 2, 3 are restored into an original signal by a decoder 4. Then the output of a frequency divider has a large probability in causing the code rule violation when the discriminated phase is not correctly selected. Since a pulse comes from a CRV terminal of the decoder 4 at every code rule violation, the signal is counted for a specific time by a discriminated phase correction circuit 11 comprising a counter 8, a timer 9, a clock changeover control signal generator 10 and a clock switch 7 and when the count exceeds a preset count, the clock is switched into a discrimination clock having a phase different by 180 deg. and even if the output of the frequency divider 6 is unstable, the discrimination phase is set correctly.
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