CHP 7 MOSFET Amplifier: 7.1 Signal Amplification

• Signal amplification (analog):

• Depending on internal structure, an amplifier can amplify input current, voltage or both
• When V x I product of output exceeds input's, power gain results
• A device must provide power gain to be called an amplifier 
• Noise tolerance through amplification:

• Another amplifier application: buffering

6.10 Power Consumption in Logic Gates

6.9 Signal Restoration, Gain and Nonlinearity

• Logic devices must incorporate both gain and nonlinearity to provide nonzero noise margins
• Logic devices must demonstrate a gain greater than unity when transition from VIL to VIH

 

• Signal Restoration and Nonlinearity

6.8 Static Analysis using SR model

• SR circuit model for invertor gate:

• SR circuit model of NAND Gate

6.7 Physical Structures of MOSFET

• The on-resistance of MOSFET depends on its physical properties (ie. geometry)
• Silicon doped with material rich in electrons is called n-type semiconductor (n+) 
• Silicon doped with material rich in holes is called p-type semiconductor (p+)

 

• Ron is the resistance of n channel
• Rn is resistance per square of n channel MOSFET in on state.
• Ron = (Rn*L)/W
• In VLSI technology, there is min fabricatable value for MOSFET channel length

SR Model of MOSFET

• S model is a gross simplification of MOSFET
• A practical MOSFET displays a non-zero resistance between its D and S terminals when it is on
• A more accurate model of MOSFET uses resistance Ron between D & S.

• SR model is still a gross simplification of MOSFET behavior.( Ron is not fixed but a function of VGS)
• Fixed resistance model is simpler and suffices for analyzing some aspect of digital circuit because the gate voltage is bimodal.
• SR model is valild only when VDS <= VGS - VT and when there is only one value for gate voltage when input is high ( VGS = VS)

6.5 Static Analysis using S model