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Analog Quick Notes
Ravi Dixit
www.learnanalog.com
MOS Operation Modes
• Cutoff if Vgs< Vt then Ids = 0
• Linear if Vgs> Vt & Vds < Vgs – Vt then
• Saturation If Vgs> Vt & Vds > Vgs – Vt then
Required Characteristics of
Amplifier
• High Gain for bandwidth of operation
• Less power consumption
• Required linear input output transfer characteristic for
less distortion
• Large output signal swing
• Less silicon area
• Noise generated by amplifier should be low
• Robust to Process, Supply & Temperature variations
• High input impedance (shouldn’t load previous stage)
• Low output impedance (should efficiently drive next
stage or load)
Single Stage Amplifier
• Common Source
• Common Drain ( Source Follower)
• Common Gate
Common Source Amplifier
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Voltage Amplifier
Input Impedance : High( Infinity)
Output Impedance : Moderate (~ Rload)
Voltage Gain : Moderate (~ - gm * Rload)
Current Gain : Infinity
Bandwidth : low ( Gate source high effective
capacitance due to miller effect )
Common Drain Amplifier
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Voltage Buffer
Also known as Source Follower
Input Impedance : High ( Infinity)
Output Impedance : Moderate (~ Rload ||1/gm)
Voltage Gain : ~ Unity (Rload / (Rload + 1/gm )
Current Gain : Infinity
Bandwidth : High
Common Gate Amplifier
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Used as a Current Buffer or Voltage Amplifier
Input Impedance : Low ( ~ 1/gm)
Output Impedance : Moderate (~ Rload )
Voltage Gain : Moderate (~ gm * Rload)
Current Gain : Unity
Bandwidth : Moderate
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