Electronic Devices and Circuits Engineering Sciences 154

Dual Aspects of Transistor Dynamics

Temporal - Usually Large Signal - Response  (Source)

Spectral (Frequency) - Usually Small Signal - Response Click on image to enlarge                                                                                                    (Source)

References:

• From Stanford University Sections 4.4 to 4.6 of A Review of MOS Device Physics (local copy) by Professor Tom Lee

 
• Relevant chapters from Professor Bart J. Van Zeghbroeck's (University of Colorado) Principles of Semiconductor Devices

 
• From the University of Pennsylvania page 43 and following in MOS Transistor Theory: Part 2 (local copy) by Professor Kenneth R. Laker.

BJT - Junction and Diffusion Capacitance

Junction or depletion layer capacitance is given by (see Section 3.3.2 in Sedra & Smith)

where

Freeze Frames from the SUNY-Buffalo applet Capacitance vs. Voltage of PN Junctions

This sequence illustrates how the capacitance evolves with bias.
For reverse bias: junction capacitance is dominant
For forward bias: diffusion capacitance is dominant

Freeze Frames from the SUNY-Buffalo applet BJT Switching Applet

This sequence illustrates how the charge stored in the base region evolves over time.
Here the transistor is switched from saturation to cut-off.

Freeze Frames from the SUNY-Buffalo applet BJT Switching Applet

This sequence illustrates how the charge stored in the base region evolves over time.
Here the transistor is switched from cut-off to saturation.

MOSFET - Junction, Diffusion and Oxide Capacitance

Click on image to enlarge  (source)

Capacitance At Cut-off For Linear (triode) Operation Under Saturation Conditions CGB (Total) CGC *CCB/(CGC + CCB) 0 0 CGD (Total) COV 0.5*CGC + COV COV CGS (Total) COV 0.5*CGC + COV 0.67*CGC + COV CSB (Total) CjSB 0.5*CCB + CjSB 0.67*CCB + CjSB CDB (Total) CjDB 0.5*CDB + CjDB CjDB  where COV = COX*W*LOVand CGC = COX*W*L

Click on image to enlarge (s)

The Miller Theorem (and "Effect") - See Sedra & Smith Section 7.4:

Suppose that we have two networks separated by a bridging element Y.  The equivalent circuits shown above represent particular important examples of such a situation.

Further, suppose that we can establish the following "gain relationship" by independent means:

and, thus, we may write

If everything else remains unchanged, this bridged configuration can be replaced by a configuration of "decoupled" networks as follows:

 where by equivalence we must have

The Classic Solution to the "Miller Effect" The Cascode Amplifier See an earlier reference