An amplifier generates a tri-level output signal in response to an input
signal that is pulse-width modulated. The amplifier is filterless and DC
free. The amplifier includes an integrator, a signal generator,
comparator, a switch pulse logic block, a driver, and a control block.
The control block supplies a multitude of pulse-width modulated (PWM)
signals in response to the received digital input signal. A pair of the
PWM signals are applied to the signal generator which in response
supplies a signal to the integrator. The integrator's output signal is
compared to a reference signal by the comparator. The switch pulse logic
block receives the output of the comparator and a pair of delayed PWM
signals and in response generates a multitude of driver signals applied
to the driver. The driver supplies an output signal that is adapted to
vary between first, second and third voltages.