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Abstract

A phase detector includes a pulse amplitude modulator and an integrator. The pulse amplitude modulator comprises a change-over switch the control input of which is fed by pulses which are subjected to mark/space modulation by means of a phase-shifted signal while the amplitude input of the pulse amplitude modulator is fed by a non-phase-shifted signal. The integrator includes an integrating amplifier, the output of which is connected by means of a capacitor to an inverting input of the integrating amplifier while the non-inverting input of the integrating amplifier is connected to ground by way of a further capacitor. The inverting and non-inverting inputs of the integrating amplifier are connected by way of respective resistors to two inputs of the integrator which in turn are connected to ground by way of respective resistors on the one hand and which on the other hand are connected by way of respective switch contacts of the change-over switch to the amplitude input of the pulse amplitude modulator. The phase detector requires only a single amplifier and may be used in phase-lock loops of static electricity meters which operate using the mark/space amplitude modulation method and which serve for the measurement of reactive energy, and which therefore require a 90.degree. phase shift provided by the phase-lock loop.

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