Patent ID: 7161519

Claim:
A PWM modulation circuit, connected to an input terminal for an analog baseband signal, and a staircase generating circuit generating a staircase wave, the modulation circuit carrying out PWM modulation to a staircase wave input from the staircase generating circuit based on an analog baseband signal input from the input terminal; wherein the staircase generating circuit comprises: a plurality of constant voltage source circuits; a plurality of switches connected to the plurality of constant voltage source circuits on a one-to-one basis; and a serial-parallel conversion circuit, carrying out serial-parallel conversion to a clock signal input from a clock signal input terminal and outputs the result to the plurality of switches; and the plurality of switches switch between their on and off states in response to a clock signal input from the serial-parallel conversion circuit; the plurality of constant voltage source circuits which are connected to the plurality of switches in an on state, output a constant voltage in a prescribed ratio, so that a staircase wave is generated, wherein the plurality of constant voltage source circuits comprise: a DC-DC converter circuit that can output voltages at a plurality of different voltage values in response to the on/off states of the plurality of switches; and a voltage control circuit that arbitrarily sets the plurality of voltage values, and in the staircase generating circuit, the DC-DC converter circuit outputs the plurality of voltages based on the voltage value in the prescribed ratio set by the voltage control circuit, so that a staircase wave is generated.