1. Kevin D. Donohue, University of Kentucky1 Frequency Analysis with SPICE Phasors, Impedance, Frequency Sweep, and SPICE

2. Kevin D. Donohue, University of Kentucky2 Recall Loop Analysis Example Determine the steady-state response for v c (t) when v s (t) = 5cos(800  t) V Result: 114.86 nF 6 k  3 k  vs(t)vs(t) + v c (t) -

3. Kevin D. Donohue, University of Kentucky3 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

4. Kevin D. Donohue, University of Kentucky4 SPICE Example Find the phasor for v c (t) for v s (t)= 5cos(2  ft) V in the circuit below for f = 100, 200, 300, 400, 500, …..1000 Hz ex16-Small Signal AC-2-Table FREQMAG(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

5. Kevin D. Donohue, University of Kentucky5 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:

6. Kevin D. Donohue, University of Kentucky6 Plot of Magnitude Linear Magnitude, Linear Frequency dB Magnitude, Log FrequencyLinear Magnitude, Log Frequency dB Magnitude, Linear Frequency

7. Kevin D. Donohue, University of Kentucky7 Plot of Phase Linear Frequency, in Degrees Log Frequency, in Degrees

8. Kevin D. Donohue, University of Kentucky8 Recall Nodal Analysis Example Find the steady-state value of v o (t) in the circuit below, if v s (t) = 20cos(4t): vsvs 10  2 i x 1 H 0.5 H 0.1 F ixix Show: v 0 (t) = 13.91cos(4t + 198.3º) +vo-+vo-

9. Kevin D. Donohue, University of Kentucky9 SPICE Example Find the phasor for v c (t) when v s (t)= 20cos(4t) V in the circuit below (note f = 2/  =0.6636) FREQMAG(I(VAM))PH_DEG(I(VAM))MAG(V(IVM))PH_DEG(V(IVM)) (Hz) +636.600m+7.589+108.440+13.912-161.560