ARRANGEMENT FOR GENERATING AN ANGLE-MODULATED CARRIER SIGNAL OF A CONSTANT AMPLITUDE IN RESPONSE TO DATA SIGNALS

摘要

An arrangement for generating an angle-modulated carrier signal of a constant amplitude and continuous phase phi (t) comprises a control circuit which in response to a given number of consecutive data symbols of symbol frequency 1/T produces addresses at a clock frequency 4q/T, where q is an integer greater than 1, and further produces phase state numbers for characterizing the value modulo-2 pi or phi (t) at the boundaries of the symbol intervals. Connected to the control circuit is a signal processor comprising a read-only memory for storing values representing cos phi (t) and sin phi (t) at the clock instants, which values are processed after reading to form the analog angle-modulated signal. An arrangement having a comparatively small capacity of the read-only memory is obtained by providing that storage in this read-only memory is only effected for non-decreasing phases phi (t) and one of the phase state numbers, that the control circuit comprises an address converter for producing addresses corresponding to this storage and a generator for producing a first and a second selection signal in response to the phase state number, and that the signal processor is arranged for selectively applying at each clock instant in response to the first selection signal only one of the two values representing cos phi (t) and sin phi (t) to a DAC-circuit and for selectively inverting at each clock instant in response to the second selection signal the sign of the output sample of the DAC-circuit, these output samples constituting the samples of the analog angle-modulated carrier signal having a carrier frequency q/T, whereby the modulated carrier signal can be derived from these output samples with the aid of a bandpass filter.