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Frequency Analysis with SPICE

Frequency Analysis with SPICE. Phasors, Impedance, Frequency Sweep, and SPICE. + v c ( t ) -. 3 k W. 114.86 nF. v s ( t ). 6 k W. Recall Loop Analysis Example. Determine the steady-state response for v c ( t ) when v s ( t ) = 5cos(800  t ) V. Result:. SPICE Solution.

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Frequency Analysis with SPICE

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  1. Frequency Analysis with SPICE Phasors, Impedance, Frequency Sweep, and SPICE Kevin D. Donohue, University of Kentucky

  2. + vc(t) - 3 kW 114.86 nF vs(t) 6 kW Recall Loop Analysis Example • Determine the steady-state response for vc(t) when vs(t) = 5cos(800t) V Result: Kevin D. Donohue, University of Kentucky

  3. SPICE Solution • Steady-State Analysis in SPICE is performed using the .AC (frequency sweep) option in the simulation set up. It will perform the analysis for a range of frequencies. • You must indicate the: • 1. Scale for uniform frequency increments • 2. Starting frequency • 3. Ending frequency • 4. Number of frequencies used in the given range. • Sources in the AC analysis must be set up in “edit simulation model” menu to: • 1. Identify source as sinusoidal • 2. Check the “use AC” option • 3. Provide a magnitude and phase Kevin D. Donohue, University of Kentucky

  4. SPICE Example • Find the phasor for vc(t) for vs(t)= 5cos(2ft) V in the circuit below for f = 100, 200, 300, 400, 500, …..1000 Hz ex16-Small Signal AC-2-Table FREQ MAG(V(IVM)) PH_DEG(V(IVM)) (Hz) (V) (deg) +100.000 +3.299 -8.213 +200.000 +3.203 -16.102 +300.000 +3.059 -23.413 +400.000 +2.887 -30.000 +500.000 +2.703 -35.817 +600.000 +2.520 -40.893 +700.000 +2.345 -45.295 +800.000 +2.182 -49.107 +900.000 +2.033 -52.411 +1.000k +1.898 -55.285 Kevin D. Donohue, University of Kentucky

  5. Plotting Frequency Sweep Results • Choices for AC (frequency sweep simulation) • For frequency ranges that include several orders of magnitude, a logarithmic or Decade (DEC) scale is more practical than a linear scale • The magnitude results can also be computed on a logarithmic scale referred to a decibels or dB defined as: Kevin D. Donohue, University of Kentucky

  6. Plot of Magnitude Linear Magnitude, Log Frequency • Linear Magnitude, Linear Frequency dB Magnitude, Log Frequency dB Magnitude, Linear Frequency Kevin D. Donohue, University of Kentucky

  7. Plot of Phase • Linear Frequency, in Degrees Log Frequency, in Degrees Kevin D. Donohue, University of Kentucky

  8. Recall Nodal Analysis Example • Find the steady-state value of vo(t) in the circuit below, if vs(t) = 20cos(4t): 10  1 H ix + vo - 0.1 F vs 2 ix 0.5 H Show: v0(t) = 13.91cos(4t + 198.3º) Kevin D. Donohue, University of Kentucky

  9. SPICE Example • Find the phasor for vc(t) when vs(t)= 20cos(4t) V in the circuit below (note f = 2/ =0.6636) FREQ MAG(I(VAM)) PH_DEG(I(VAM)) MAG(V(IVM)) PH_DEG(V(IVM)) (Hz) +636.600m +7.589 +108.440 +13.912 -161.560 Kevin D. Donohue, University of Kentucky

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