0pamp_wb_au_211

0pamp_wb_au_211 - Characterizing Differential Amplifiers...

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Cadence Design Systems, Inc. Characterizing Differential Amplifiers for Communications Circuits Measuring Performance with Simulation for First Pass Success Jonathan David
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2 Topics § § § Using the Test bench § PVT (Process,Voltage,Temperature) Validation § Advanced Measurements § Using OCEAN Scripts § Summary
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3 First Pass Success and Design Reuse are needed to Meet Present Challenges § Large Mixed Signal Chips § Smaller Market Windows § Short Development Cycles § Lower Supply Voltages § Smaller Processes § Higher Performance § Less Power Background 1
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4 Performance Verification is our Strategy § Spectre Simulator § Analog Artist UI § OCEAN scripts § Verilog-A behavioral Language § Diva LPE § We need to Simulate the same circuits we Fab. Background 2
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5 Differential Amp is Basic to Comms § Switched Capacitor A/D’s § Differential Signal Paths Common-Mode Feedback is required Background 3
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6 Amp Specifications are no secret IP3 SFDR THD ENI f BI ENV f BV I Supply vs PVT Min V supply V OMax I SC Output Compliance CMR Common Mode Range Overshoot Settling Time Slew Rate F MAX Zin Zout I B I OS I IO Drift V OS vs Proc/Mmatch V OS vs Temp V IO Drift GB A OL φ OL vs. Freq. A d A c
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7 IP3 SFDR THD ENI f BI ENV f BV I Supply vs PVT Min V supply V OMax I SC Output Compliance CMR Common Mode Range Overshoot Settling Time Slew Rate F MAX Zin Zout I B I OS I IO Drift V OS vs Proc/Mmatch V OS vs Temp V IO Drift GB A OL φ OL vs. Freq. A d A c
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8 Simplest Test Bench is Unity Gain Circuit § Key to Understanding the Full Test Bench. Key Specs 1
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9 Key Specs 2
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10 Offset Amplification Lowers Output Error § acOpenDiff written in Verilog-A provides: – Output provides Gain for Offset voltage during DC-OP. – Output is “DC” for AC simulation, and Noise. – thus opening the loop. – Unity gain for Transient. vos E = 100 vcm vcm+vos/2 vcm-vos/2 vos/100 vout E = 0.5 Key Specs 3
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11 Variables are key to TB Flexibility TB Use
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12 DC Operation Point Signal Loop x100 TB Use
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13 Vos Drift § § Differential Amps Ideally have no Offset. . Introduce some. VosDrift = value(deriv(VS(“/vos”)) 27) = -54n V/°C TB Use
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14 AC Open Loop Signal Path AC DC TB Use
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15 Open Loop Gain, Phase + Margins § Calculate Av UGB GM, PhaseM, GBW § Plot Aol Φ ol Av = value(db20(VF(“/outp”) –VF(“/outn”)) 0) GBW = gainBwProd(VF(“/outp”) –VF(“/outn”)) UGB = cross(db20(VF(“/outp”) –VF(“/outn”)) 0 1 “either”) GM = gainMargin(VF(“/outp”) –VF(“/outn”)) Φ M = phaseMargin(VF(“/outp”) –VF(“/outn”)) DomPole = bandwidth((VF(“/outp”) –VF(“/outn”)) 3 “low”) These require V(inp,inn) = 1 over entire Range Or use: (VF(“/outp) – VF(“/outn”)) / (VF(“/inp”) – VF(“/inn”)) TB Use
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0pamp_wb_au_211 - Characterizing Differential Amplifiers...

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