Static (DC)
 Dynamic (AC)
Linear
 Error
Source
 Offset Voltage
DC Bias Current
 Finite Bandwidth
Text
 Sec. 2.8
 Sec. 2.6
Analysis
Strategy
  1. Add DC sources to ideal op-amp to model errors

  2. Analyze with superposition to find contribution of each error source to output voltage

  3. Add in "worst case" fashion
  • Offset voltage can be either polarity

  • Bias current polarity known from type of op-amp input stage
 Model closed loop behavior with first-order transfer function:
  • DC gain from ideal op-amp assumptions

  • Closed loop 3dB frequency fBCL from gain-bandwdith product relationship
Gain-bandwidth product procedure:
  1. Redraw circuit with all inputs suppressed (set = 0)

  2. Find feedback factor β (fraction of output fed back to inverting input)

  3. Closed loop bandwidth fBCL will be unity gain frequency ft mutliplied by β
Non-Linear
 Error
Source
 Output voltage swing limit
Output current limit
 Slew rate limit
Text
 Sec. 2.7
Analysis
Strategy
  1. Determine maximum total vOUT, iOUT, excursion at op-amp output from linear system model

  2. Compare maximum, minimum to op-amp limits
  1. Determine vOUT(t) from linear system behavior (transfer function for sine wave, general exponential response for step)

  2. Calculate time derivative dvOUT(t)/dt

  3. Compare maximum, minimum dvOUT(t)/dt to op-amp slew rate limit