A bitstream converter for converting a 1-bit pulse density modulated (PDM) bitstream signal into an analog audio signal, the bitstream converter comprising: a processor configured to process the 1-bit PDM bitstream signal using a return to zero clock having a frequency higher than a sampling frequency of the 1-bit PDM bitstream signal to output a corresponding 1-bit return to zero signal, wherein the processor is configured to process the 1-bit PDM signal to ensure a portion of each bit of the 1-bit PDM bitstream signal is zero for a duration which is based on the frequency of the return to zero clock; and signal processing means configured to extract the analog audio signal from the 1-bit return to zero signal by filtering the 1-bit return to zero signal.

Provided is a circuit which can correct an output state in real time and reduce influences of distortion/noise components generated by a delay device. A signal modulation circuit includes a subtractor, an integrator, a phase inverting circuit, a DFF for while inserting a zero level at timing synchronous with the clock signal, delaying and quantizing the signal, a ternary signal generating circuit for generating a ternary signal for selectively driving a load connected to a single power supply into ternary conductive states including a positive current on-state, a negative current on-state, and an off-state, a driver circuit for generating a driving signal for driving a load, and a feedback circuit for feeding back the driving signal from the driver circuit to the input signal.