Method for locking a synthesised output signal of a synthesised waveform synthesiser in a phase relationship with an input signal, and a digital waveform synthesiser for producing a synthesised output signal in a phase relationship with an input signal

A digital waveform synthesiser for producing a synthesised output signal 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,
• an input terminal for receiving the externally generated input signal,
• a comparing circuit for comparing a signal indicative of the phase of the synthesised output signal with a signal indicative of the phase of the input signal, and
• a control circuit for applying an initial value of the frequency control digital word to the direct digital synthesiser, and being responsive to the comparing circuit for subsequently and sequentially applying progressively altered values of the frequency control digital word to the direct digital synthesiser until the synthesised output signal produced by the direct digital synthesiser is substantially in the phase relationship with the input signal.

A digital waveform synthesiser for producing a synthesised output signal waveform of a frequency for applying to an external circuit to produce a selectable frequency dependent response from the external circuit, 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 to be applied to the external circuit,
• a feedback terminal for receiving a signal indicative of the frequency dependent response of the external circuit to the synthesised output signal applied thereto,
• a comparing circuit for comparing a characteristic of the signal indicative of the frequency dependent response of the external circuit with a signal indicative of a corresponding characteristic of the synthesised output signal, and
• a control circuit for applying an initial value of the frequency control digital word to the direct digital synthesiser, and being responsive to the comparing circuit for subsequently and sequentially applying progressively altered values of the frequency control digital word to the direct digital synthesiser until the synthesised output signal produced by the direct digital synthesiser is of frequency to produce the selected frequency dependent response in the external circuit.