PWM digital amplifier with high-order loop filter

A PWM digital amplifier for amplifying a digital signal, the digital amplifier comprising:

• a multiple input junction for additively receiving digital currents generated from input voltage signal Ei and a feedback voltage signal Ef;
• a multi-stage amplifier loop filter including a first integrator with a integrator input node connected to the multiple junction for receiving a summed value of the digital currents and a final integrator outputting an amplified signal,
• a comparator with a first comparator input node connected to an integrator output node of the final integrator to receive the amplified signal and a second comparator input node connected to a sawtooth signal generator, the comparator outputting a pulse width modulated and amplified signal;
• a voltage switch including a voltage switch input connected to the comparator output node;
• a multiple feedback loop junction connecting to the voltage switch output;
• a feedback branch connecting the multiple feedback loop junction to the multiple input junction;
• a passive low pass filter having an input connected to the multiple feedback loop junction;
• a speaker having an input connected to the low pass filter output;
• the mult-stage amplifier loop filter and comparator characterized by the pulse width modulated and amplified signal having a magnitude value no less than 20 dB over a range of frequencies.

A pulse-width modulated digital amplifier comprising:

• a multi-stage loop filter for producing a stable loop output signal Ew from an input digital signal Ei,
• a comparator for receiving loop output signal Ew and a pre-selected signal, the comparator generating a pulse-width modulated signal Ep from the preselected signal and signal Ew,
• a switching output stage for receiving pulse-modulated signal Ep and generating an output signal Eo;
• and
• a feedback loop for channeling a portion of the signal Eo external to the loop filter through a passive element and combining with the input signal Ei;
• the multi-stage loop filter and comparator characterized by the pulse width modulated signal having a magnitude value no less than 20 dB over a range of frequencies.