Fig. 4
From: Low-power transcutaneous current stimulator for wearable applications
Schematic for a high-voltage, low-power transcutaneous current stimulator for wearable applications. Block A is a differential low-pass filter. Block B is a modified Howland current pump. The circuit takes advantage of bootstrapping transistors to enable low voltage differential amplifiers to operate at high voltage. Furthermore, the addition of an inverting amplifier (Block C) driving the reference electrode, allows the full supply voltage to be applied over the load in both directions, halving the requirement for the supply voltage