# Parasitic Capacitance Models

## Channel Charge Capacitance

Take Aways :

Interesting Facts

• $C_{ox} = \frac{e_{ox}}{t_{ox}}$

Reference

Others

Capacitance generated between Channel(Source, Drain, Bulk) and Gate.

In cutoff there isn’t any channel present and therefore there is Cgc between gate and body.

In linear region inversion layer if formed. The Layer is between source and drain. Thus gate to body capacitance is 0 and total Cgc is distributed evenly between source and drain.

In saturation mode, channel is pinched off and Capacitance between gate and drain is 0 and gate and body is 0 this there is capacitance gate and source.

## Diffusion Capacitance Model

Take Aways :

• $C_{bottom} = C_{j}.W.L_{source}$
• $C_{gw}= C_{jsq}x(W+2L_{source})$
• $C_{diff}= C_{gw} + C_{bottom}$
• Drain – $latex C_{diff} = C_{j}L_{drain}W + C_{jsw}(W+2L_{drain}) • Source –$latex C_{diff} = C_{j}L_{source}W + C_{jsw}(W+2L_{source})

Reference

Junction Capacitance–Reverse biased source-body and drain-body pn junctions.

Non Linear

Decreases when reverse bias is increased.