Mixed Signal Chip Design Lab Operational Amplifier Configurations Jaehyun Lim, Kyusun Choi Department of Computer Science and Engineering The Pennsylvania State University CSE598A/EE597G Spring 2006

Mixed Signal Chip Design Lab Ideal Op-Amp infinite voltage gain (A = ∞, V - =V + for finite V O ) infinite input impedance ( i - = i + = 0) zero output impedance infinite bandwidth zero input offset V-V- V+V+ VOVO i-i- i+i+ V O = A(V + - V - )

Mixed Signal Chip Design Lab Ideal Op-Amp  Inverting Amplifier Configuration current through R 1 = current through R f ( ∵ i - = i + = 0) (V in -V 1 ) / R 1 = (V - -V O ) / R f and V - = V + = 0 V O = -(R f / R 1 )·V in V in R1R1 RfRf V-V- VOVO

Mixed Signal Chip Design Lab Ideal Op-Amp  Non-Inverting Amplifier Configuration current through R 1 = current through R f ( ∵ i - = i + = 0) (V O -V - ) / R f = V - / R 1 and V - = V + = V in V O = (1 + R f / R 1 )·V in V in R1R1 RfRf V-V- VOVO

Mixed Signal Chip Design Lab Ideal Op-Amp  Voltage Follower (Unit Gain Buffer) unit-gain non-inverting amplifier V O = V in V in VOVO

Mixed Signal Chip Design Lab Non-Ideal Op-Amp  Real World gain is not infinite  V - ≠ V + gate current  i + ≠ 0, i - ≠ 0 (but still negligible) finite bandwidth  requires frequency compensation

Mixed Signal Chip Design Lab Non-Ideal Op-Amp  Inverting Amplifier Configuration V O = A(V + - V - )  V - = -V O / A (V in - V - ) / R 1 = (V - - V O ) / R f V O = -R f /R 1 1+(1+R f /R 1 )/A V in note that if A → ∞, V O → -(R f / R 1 )V in V in R1R1 RfRf V-V- VOVO

Mixed Signal Chip Design Lab Non-Ideal Op-Amp  Non-Inverting Amplifier Configuration V O = A 1+ V in note that if A → ∞, V O → (1+R f / R 1 )V in V in R1R1 RfRf V-V- VOVO R1R1 R 1 +R f A

Mixed Signal Chip Design Lab Op-Amp with Single Supply  Inverting Amplifier Configuration V in R1R1 RfRf VOVO R R V dd / 2

Mixed Signal Chip Design Lab Op-Amp with Single Supply  Non-Inverting Amplifier Configuration R R V dd / 2 V in RfRf VOVO

Mixed Signal Chip Design Lab Op-Amp with Single Supply  Amplifier Design well-designed amplifier should have a transition point centered at V dd / 2 V V V+V+ V dd / 2 VOVO V+V+ VOVO V dd

Mixed Signal Chip Design Lab Op-Amp with Single Supply  Examples from Last Class voltage comparator – V + = 2.5 V  V O = ? – V + = V  V O = ? – V + = V  V O = ? V+V+ VOVO 2.5 V 5 V

Mixed Signal Chip Design Lab Op-Amp with Single Supply  Examples from Last Class ideal case (gain = ∞) V + = 2.5 V  V O = 2.5 V (V + = V - for finite V O and V O centered at 2.5 V) V + = V  V O = A(V + -V - ) = ∞  V O = 5 V (limited to supply) V+ = V  V O = A(V + -V - ) = -∞  V O = 0 V (limited to supply) V+V+ VOVO 2.5 V 5 V ∞

Mixed Signal Chip Design Lab Op-Amp with Single Supply  Examples from Last Class gain A = 1000 V + = 2.5 V  V O = 2.5 V (V O centered at 2.5 V) V + = V  V O = (V + -V - ) = 3.5 V V+ = V  V O = (V + -V - ) = 1.5 V V+V+ VOVO 2.5 V 5 V A

Mixed Signal Chip Design Lab Op-Amp with Single Supply  HSpice Simulation V+V+ VOVO.DC analysis centered at 2.5 V gain ≈ 1,175 V + = V  V O = V V + = V  V O = V