Pulse and Digital Circuits

1.10 STRAY CAPACITANCES IN DEVICES

The semiconductor diode is used as a switch. In a forward-biased diode, there is a diffusion capacitance C_D that depends on the forward current of the diode. However, while considering the equivalent circuit of the diode at high frequencies, this capacitance will have a negligible say. But in a reverse-biased diode, there exists a transition capacitance C_T which is inversely proportional to the diode reverse-bias voltage and is taken into consideration at high frequencies. Hence, the high-frequency equivalent circuit of a reverse-bias semiconductor diode is given in Fig. 1.52. The stray capacitances limit the switching speed. Here, R_r is the reverse resistance of the diode.

Similarly, we have stray capacitances ...