Patent ID: 7283012

Claim:
A tri-state pulse density modulator for generating a pulse density modulation (PDM) output signal, comprising: an adder for receiving a PDM input signal and a latched input signal to generate an output sum signal and a carry signal; a latch module coupled with the adder for latching the output sum signal with a clock signal to generate the latched input signal; a first switch device coupled to a first voltage; a second switch device serially coupled between the first switch device and a second voltage that is lower than the first voltage; and a control circuit module responsive to the carry signal for selectively turning off the first and second switch devices to generate the PDM output signal at a tri-state voltage between the first and second voltages, or turning on the first or second switch device to generate the PDM output signal at the first or second voltage, respectively, so that the PDM output signal only switches between the tri-state voltage and either the first voltage or the second voltage.