5. CMOS Operational Amplifiers - IMS

5. CMOS Operational AmplifiersAnalog Design for CMOS VLSI SystemsFranco Maloberti5. CMOS Operational Amplifiers1 Analog Design for CMOS VLSI SystemsFranco MalobertiBasic op-ampThe ideal Operational amplifier is a voltage controlledvoltage source with infinite gain, infinite input impedanceand zero output op-amp is always used in feedback CMOS Operational Amplifiers2 Analog Design for CMOS VLSI SystemsFranco MalobertiTypical feedback configuration V0=V2Z4Z3+Z4Z1+Z2Z1 V1Z2Z1 The error due to the finite gain is proportional to 1 / A0. Thiserror must be smaller than the error due to impedancemismatch. V0=V2Z4Z3+Z4Z1+Z2Z1 V1Z2Z1 1+Z1+Z2A0Z1 Finite gain effect:5. CMOS Operational Amplifiers3 Analog Design for CMOS VLSI SystemsFranco MalobertiOTAIf impedances are implemented with capacitors andswitches, after a transient, the load of the op-amp is madeof pure capacitors. The behavior of the circuit does notdepend on the output resistance of the op-amp and stageswith high output resistance ( Operational transconductanceamplifiers) can be CMOS Operational Amplifiers4 Analog Design for CMOS VLSI SystemsFranco MalobertiTransient Vi(0+)=VinC1C1+C//C0 Vo(0+)=Vi(0+)CC0+C Vi( )=VinC1+CC1+C(1+gmr0) Vo( )= Vi( ) gm r0 C0gm5.

5. CMOS Operational Amplifiers 1 Analog Design for CMOS VLSI Systems Franco Maloberti Basic op-amp The ideal operational amplifier is a voltage controlled voltage source with infinite gain, infinite input impedance and zero output impedance. The op-amp is always used in feedback configuration.

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