An output circuit for use in an implantable cardiac defibrillation
provides an output pulse having a waveform of virtually any desired
shape. The device includes a sensing circuit that senses cardiac
activity. An arrhythmia detector detects fibrillation responsive to the
cardiac activity signal. The device further includes an output circuit
that provides a stimulation output pulse when the arrhythmia detector
detects a cardiac arrhythmia. The output circuit includes an H-bridge
having a pair of switching devices which control the output pulse
waveform with pulse-width modulation and a second pair of switching
devices that control the output pulse polarity.