Patent ID: 8428213
Filing Date: 2013-04-23
Classification: G06F,H03K,H03L

Abstract:
1. A method for locking a synthesised output signal of a digital waveform synthesiser in a phase relationship with an externally generated input signal, the digital waveform synthesiser comprising a direct digital frequency synthesiser responsive to a frequency control digital word applied thereto for producing the synthesised output signal, the method comprising: applying an initial value of a frequency control digital word to the direct digital synthesiser, and sequentially applying progressively altered values of the frequency control digital word to the direct digital synthesiser until the synthesised output signal is substantially in the phase relationship with the input signal, wherein each subsequent value of the frequency control digital word is a function of the current value thereof, wherein the value of the frequency control digital word is increased from the current value thereof in response to the synthesised output signal being in a first state in which the period thereof is greater than 1/H times the period of the input signal, and the frequency control digital word is decreased from the current value thereof in response to the synthesised output signal being in a second state in which the period thereof is less than 1/H times the period of the input signal, where H is a whole number of value from one upwards.