U.S. Philips Corporation

Gunter Hildebrandt

Karl-Heinz Rehfeldt

Heinz H Gehrt

Holger Gehrt

Herbert Heinemann

For purposes of simple construction and universal application, a circuit arrangement for frequency conversion of a color signal to a second carrier frequency, this color signal being present in picture lines and including a color burst and a chrominance information signal modulated on a chrominance sub-carrier of the first carrier frequency, the circuit arrangement being switchable in a mode for conjugate-complex formation in which it generates an output signal in which, additionally to the frequency conversion, the color signal has a phase position in accordance with the standard, which alternates from picture line to picture line, and which color signal is present in a conjugate-complex form in every second picture line, is characterized in that

Circuit arrangement for frequency conversion of a color signal

A circuit arrangement which includes an FM demodulator having a delay circuit which subjects the received FM signal to a preset time delay and a signal combining circuit which combines the delayed and undelayed FM signal to derive a combined signal the mean value of which is proportional to the frequency of the FM signal. A low pass filter derives the demodulated signal from such combined signal. The proportionality factor is determined by the preset time delay, which is controllable by a control signal supplied to the delay circuit by a datum level detector which detects a selected datum level of the demodulated signal; for example, the lowest level of such signal. By controlling the time delay in accordance with such datum level, the datum level detector thereby stabilizes the maximum amplitude of the demodulated signal relative to the datum level thereof despite variations in the maximum frequency swing of the received FM signal.

FM demodulator with carrier shift compensation

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

Gunter Hildebrandt