| 摘要 |
<p>19 Frequency synthesiser. A frequency synthesiser of the type employing a cycle cancellation technique and providing a correction signal which at least reduces the jitter in the output frequency caused by each cancelled cycle. A control device (CD) causes cycles to be added (PA) and cancelled (PS) without affecting the average frequency (Fc). A compensation signal for the resultant jitter is also generated (DAC and I) which is combined with the correction signal in an adder (AS) and with the frequency control voltage signal from the phase comparator (PC) in a further adder (ASD). These added/cancelled pulses cause any residual discrete spurious signal, resulting from the system imbalance, to be spread over a wide spectrum to appear as noise at a very low level. Also the settling time of the synthesiser after a frequency change is increased in some types of synthesiser.</p> |
