Abstract: A wireless communication unit comprises a frequency generation circuit employing a fractional-based synthesiser, a voltage controlled oscillator circuit and a charge pump. A characterising function characterises a charge pump gain at a number of synthesized frequencies. A memory element is arranged to store characterised parameters. A scaling function is operably coupled to the memory element and the voltage controlled oscillator circuit and arranged to compensate for Kv/N variation over a tuning line voltage applied to the voltage controlled oscillator circuit, at a synthesized frequency. In this manner, the bandwidth (open loop gain) of a Phase Locked Loop remains relatively constant, to ensure the phase noise and lock time performance of the transmitter is better than 50 ?sec and the Rx performance is better than 125 ?s. Advantageously, only one loop filter is required to cover both Rx and Tx modes of operation.

Abstract: A charge pump arrangement for a phase-locked-loop has a current source circuit (60) which provides charging current to the phase locked loop, and a current sink circuit (90) which depletes charging current from the phase locked loop. The current source circuit (60) and the current sink circuit (90) have slew rates which have a predetermined relationship. In this way, the charge pump causes substantially no non-linear charge injection in the phase-locked-loop. Cascoded current mirrors (75, 85) are utilised to provide a high voltage with thin gate oxide technology. The arrangement has a relatively small die size. Since bias currents of the arrangement are mirrored according to the output current required, improved transient times are produced, leading to reduced phase noise.

Abstract: A charge pump arrangement for a phase-locked-loop has a current source circuit (60) which provides charging current to the phase locked loop, and a current sink circuit (90) which depletes charging current from the phase locked loop. The current source circuit (60) and the current sink circuit (90) have slew rates which have a predetermined relationship. In this way, the charge pump causes substantially no non-linear charge injection in the phase-locked-loop. Cascoded current mirrors (75, 85) are utilised to provide a high voltage with thin gate oxide technology. The arrangement has a relatively small die size. Since bias currents of the arrangement are mirrored according to the output current required, improved transient times are produced, leading to reduced phase noise.