Acquisition performance of 2nd-order phase-locked loops in the presence of time delay for switched and swept signal conditions

The paper describes the acquisition behaviour of 2nd-order phase-locked loops with time delay ¿ for two different conditions of the input signal. When the input signal appears instantaneously, i.e. a process we have termed `switched¿ acquisition, the pull-in range limit obtained by Develet of ¿/4 Hz is confirmed. However, when the input signal is moved or swept towards the loop VCO frequency (or vice-versa), a distinct phenomenon, which we have termed `swept¿ pull-in, has been observed. For a large gain type 1 or type 2 loop, it is shown that, for frequency offsets greater than ¿/4 Hz, the loop will not lock unless a minimum sweep rate is exceeded.