Some fundamentals of medical electronics. II. Differentiating and integrating circuits, simple AC circuits.

In the previous article in this series, the charge and discharge of a condenser via a resistance was considered. It was assumed that ample time was available for the charge or discharge to take place. The product (capacity in microfarads x resistance in megohms) has the dimensions of a time in seconds, and is known as the "timeconstant" of the circuit. After charging for a period equal to one time-constant, the voltage appearing across the condenser will equal 63 per cent of the final value. Consider the application of a rectangular voltage pulse to the combination of a condenser C in series with a resistance R as in figure lb. Such a pulse in which the voltage rises suddenly from one value to a higher value, and then returns suddenly after a definite time, is typical of the waveform provided repetitively