To realize spread spectrum modulation and pulse width modulation in a pulse signal generating circuit.

A digital random signal S0 output from a pseudo-random number generator 10 is converted into an analogue random voltage S1 through a D/A converting circuit 20. An adder 30 adds a signal S1 and a central frequency setting voltage S2 to output a frequency control voltage signal S3. A saw-tooth wave generating circuit 40 generates a saw-tooth-wave voltage whose frequency varies in accordance with the signal S3. A comparator 50 outputs a pulse signal S6 depending on magnitudes of the saw-tooth-wave voltage S4 and a duty ratio setting voltage S5. The pulse signal S6 has a duty ratio corresponding to the duty ratio setting voltage and varies in frequency in response to the frequency control voltage signal S3.

COPYRIGHT: (C)2008,JPO&INPIT