A DIGITAL FREQUENCY SYNTHESISER AND A METHOD FOR PRODUCING A FREQUENCY SWEEP

摘要

A single chip digital frequency synthesiser (1) for synthesising a frequency swept synthesised output signal of a selectable frequency sweep comprises a direct digital synthesiser (5) which produces the frequency swept synthesised output signal on an output terminal (7) in response to values of a frequency control digital word applied to a frequency control input (8) thereof by an on-chip data processing circuit (25). An on-chip programmable data storing circuit (12) is programmable to store data indicative of a selected mode in which the digital frequency synthesiser (1) is to operate, and to store data indicative of selectable frequency and the time domains of the frequency swept synthesised output signal to be produced. The data processing circuit (25) reads the mode of operation and the frequency domain data and if appropriate the time domain data of a frequency swept synthesised output signal to be produced by the digital frequency synthesiser (1) from the data storing circuit (12), and computes the values of the frequency control digital word and the sequence in which the values of the frequency control digital word are to be applied to the direct digital synthesiser (5). Depending on the mode of operation, the data processing circuit (25) determines the rate at which the values of the frequency control digital word are to be applied to the direct digital synthesiser (5) in response to a logic control signal applied to a control terminal (20) or as a function of a number of clock cycles of a system clock signal applied on a system clock terminal (10) or a number of cycles of the frequency swept synthesised output signal. The frequency swept synthesised output signal may also be produced in frequency bursts.