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Lect2UP250_(100328)

# Lect2UP250_(100328) - Lecture 250 Measurement and...

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Lecture 250 – Measurement and Simulation of Op amps (3/28/10) Page 250-1 CMOS Analog Circuit Design © P.E. Allen - 2010 LECTURE 250 – SIMULATION AND MEASUREMENT OF OP AMPS LECTURE ORGANIZATION Outline • Introduction • Open Loop Gain CMRR and PSRR • A general method of measuring A vd , CMRR , and PSRR • Other op amp measurements • Simulation of a Two-Stage Op Amp • Op amp macromodels • Summary CMOS Analog Circuit Design, 2 nd Edition Reference Pages 310-341 Lecture 250 – Measurement and Simulation of Op amps (3/28/10) Page 250-2 CMOS Analog Circuit Design © P.E. Allen - 2010 INTRODUCTION Simulation and Measurement Considerations Objectives: The objective of simulation is to verify and optimize the design. The objective of measurement is to experimentally confirm the specifications. Similarity between Simulation and Measurement: Same goals Same approach or technique Differences between Simulation and Measurement: Simulation can idealize a circuit - All transistor electrical parameters are ideally matched - Ideal stimuli Measurement must consider all nonidealities - Physical and electrical parameter mismatches - Nonideal stimuli - Parasistics

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Lecture 250 – Measurement and Simulation of Op amps (3/28/10) Page 250-3 CMOS Analog Circuit Design © P.E. Allen - 2010 OPEN LOOP GAIN Simulating or Measuring the Open-Loop Transfer Function of the Op Amp Circuit (Darkened op amp identifies the op amp under test): Simulation: This circuit will give the voltage transfer function curve. This curve should identify: 1.) The linear range of operation 2.) The gain in the linear range 3.) The output limits 4.) The systematic input offset voltage 5.) DC operating conditions, power dissipation 6.) When biased in the linear range, the small-signal frequency response can be obtained 7.) From the open-loop frequency response, the phase margin can be obtained ( F = 1) Measurement: This circuit probably will not work unless the op amp gain is very low. Fig. 240-01 + - V OS v IN v OUT V DD V SS R L C L Lecture 250 – Measurement and Simulation of Op amps (3/28/10) Page 250-4 CMOS Analog Circuit Design © P.E. Allen - 2010 A More Robust Method of Measuring the Open-Loop Frequency Response Circuit: v IN v OUT V DD V SS R L C L R C Fig. 240-02 Resulting Closed-Loop Frequency Response: dB log 10 ( w ) A v (0) 1 RC RC A v (0) Op Amp Open Loop Frequency Response Fig. 240-03 0dB Make the RC product as large as possible.
Lecture 250 – Measurement and Simulation of Op amps (3/28/10) Page 250-5 CMOS Analog Circuit Design © P.E. Allen - 2010 CMRR AND PSRR Simulation of the Common-Mode Voltage Gain V OS v out V DD V SS R L C L + - v cm + - Fig. 6.6-5 Make sure that the output voltage of the op amp is in the linear region. Divide (subtract dB) the result into the open-loop gain to get CMRR . Lecture 250 – Measurement and Simulation of Op amps (3/28/10) Page 250-6 CMOS Analog Circuit Design © P.E. Allen - 2010 Simulation of CMRR of an Op Amp None of the above methods are really suitable for simulation of CMRR .

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