U.S. Philips Corporation

Heinz H Gehrt

Karl-Heinz Rehfeldt

Gunter Hildebrandt

A circuit arrangement for a picture reproducing apparatus having an amplitude limited (7), to which a frequency-modulated picture signal is applied and whose output is coupled to a frequency demodulator (8, 9). The output signal of the amplitude limiter (7) is applied to a low-pass filter (12) via a delay means (8) which may form part of the frequency demodulator (8, 9), the output signal of the low-pass filter following fluctuations in time-average of the output signal of the delay means (8). The delay time of the delay means (8) is of the order of magnitude of a quarter of the carrier period of the frequency-modulated picture signal. The output signal of the low-pass filter (12) constitutes the threshold value of the amplitude limiter (7), the polarity of the output signal of said limiter being changed when the frequency-modulated picture signal intersects said threshold value.

Circuit arrangement for frequency-modulated picture signals

A multivibrator circuit used as a delay element. A pair of complementary signals to be delayed control the transistors of a long tailed pair so as to generate charging and discharging currents for a capacitance coupled between first and second current branches of the multivibrator circuit. The delay time depends, among other parameters, on the exact values of these currents. In order to avoid the necessity of providing very accurate values of the signals for generating the proper current values, a current division is applied, to the circuit by adding in parallel to each long tailed pair transistor, a constant current source. As a result the currents in the multivibrator circuit can be switched between two exactly determined current values by alternately switching the long tailed pair transistors fully on and off. The same kind of current division is applied to the circuit in order to achieve a voltage swing at the output which is independent of the current adjustment.

Multivibrator circuit having compensated delay time

A circuit arrangement for detecting whether the frequency of an input signal exceeds a predetermined frequency swing. The arrangement includes a detector circuit which supplies an error-indication signal if the phase shift between the input signal and a second signal, which second signal tracks the frequency of the input signal, exceeds limit values corresponding to such frequency swing. A delay circuit derives the second signal from the input signal by delaying the input signal a predetermined delay time which increases with the frequency of the input signal.

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Hamburg, Germany

Heinz H Gehrt