Abstract: A phase-locked loop employing a charge pump 7 for synthesizing RF channels permits a low supply voltage to be used by using two amplifier stages 5a, 5b, between the charge pump and a VCO4. Stage 5a may be a high impedance common emitter pair of complementary transistors allowing a wide voltage swing. Stage 5b may be an operational amplifier with resistive feedback to provide gain less than unity and a low impedance output to provide feedback around a loop filter 6 to source the current from charge pump 7 entering an inverting input of stage 5a. Alternatively, stages 5a, 5b may be reversed.

Abstract: In a D.C. restoration circuit for a digital FM radio receiver, in which demodulated signals may be presented at the output of the demodulator as low-level differential signals superimposed on a variable D.C. level, the differential signal paths are capacitively coupled to the inputs of a comparator, and the voltage excursions at these inputs are clamped when the voltage between the inputs exceeds a predetermined value.

Abstract: A charge pump circuit for a frequency/phase comparator in a phase locked loop oscillator arrangement, in which current sources utilizing only npn transistors provide currents of equal magnitude but of opposite sense to an input of an operational amplifier, the output of this amplifier charge-pumping a capacitor to control the frequency of oscillation of an oscillator. The use of npn transistors enables higher current levels and higher speed switching compared to circuits including pnp transistors.

Abstract: A phase detector for a phase locked loop frequency synthesizer, in which frequency-divided signals from a variable frequency oscillator and a reference oscillator are used to trigger respective ramp waveform generators, and a sample pulse generator is arranged to be responsive to the reference ramp waveform to provide sample pulses centered at the mid-point of that ramp waveform to respective sample and hold circuits, the relative phases of the ramp waveforms being determined from the sampled and held voltages.