Output stage for heart pacemaker - has complementary pair of transistors to use discharge current for stimulation

This circuit of an output stage of a battery driven heart pacemaker fully exploits the electrical energy normally wasted when a coupling capacitor is allowed to discharge. In this circuit both the leading and trailing edge of the pulse which forms the input to this circuit are used to produce spikes to stimulate the heart muscle. The capacitor (3) is charged by the battery voltage (Ub) through the heart impedance (1) whilst a transistor (4) is turned on by the rising edge of the pulse. At the end of this charging period another, complimentary transistor (5) is turned on by the falling edge of this pulse, resulting in discharge through the heart impedance. The time constant formed by the product of the capacitance and the heart impedance is about one third of the pulse width.