Tri-state pulse density modulator

A tri-state pulse density modulator for generating a pulse density modulation (PDM) output signal, comprising:

• an adder for receiving the 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,
• wherein the control circuit module receives a sign bit for determining if the PDM output signal switches between the tri-state voltage and the first voltage, or between the tri-state voltage and the second voltage.

A method for generating a pulse density modulation (PDM) output signal, comprising:

• generating a carry signal having a pulse density representing an PDM input signal;
• generating a sign bit signal indicating the polarity of the PDM output signal;
• and
• generating one or more control signals responsive to the carry signal and the sign bit signal for controlling a first switch device coupled to a first voltage, and a second switch device serially coupled between the first switch device and a second voltage that is lower than the first voltage,
• wherein the control signals selectively turn 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 turn 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.