Problem 14.6 - Fourth-Order Butterworth Filter Response to Square Wave
*
* NOTE: This is a two-part problem.
* 1. Use the PWL function to describe a periodic square wave as
* input to a Butterworth filter. Use PROBE to obtain the frequency
* spectra of the input and output waveforms.
* 2. Determine the input and output frequency spectrum of a Butter-
* worth filter when the input consists of three series-connected
* sinusoidal generators at the frequencies of the first three
* nonzero frequency components of an ideal symmetric square wave.
*
* A Butterworth filter has a sharp cut-off characteristic that will
* discriminate between closely spaced frequencies of an input signal.
* For an 800-Hz square wave input, the first three nonzero terms of
* the Fourier series of the square wave are 800, 2400, and 4000 Hz.
* The amplitudes of the components are 1.0, 1/3, and 1/5,
* respectively.
*
* Use the PWL function (then the SIN function) and .TRAN analysis. Use
* PROBE to plot the input and output waveforms for Butterworth filter
* and to obtain the frequency spectra of each of the waveforms.
*
* Prob. 14.6, Part 1. Fourth-Order Butterworth Filter Response to Square Wave
.OPT NOPAGE NOBIAS
V1 1 0 PWL(0 0 .5E-6 1 625E-6 1 626E-6 -1 1.25E-3 -1
+ 1.251E-3 1 1.875E-3 1 1.876E-3 -1 2.5E-3 -1
+ 2.501E-3 1 3.125E-3 1 3.126E-3 -1 3.75E-3 -1
+ 3.751E-3 1 4.375E-3 1 4.376E-3 -1 4.9995E-3 -1
+ 5.0E-3 0
R1 ; Enter the device statements for the
R2 ; Butterworth filter circuit.
R3
C1
C2
E1
R4
R5
R6
C3
C4
E2
.TRAN ; Complete the .TRAN command for an
; analysis over a 5-millisecond period.
.PROBE
.END
Prob 14-6, Part 2. Fourth-Order Butterworth Filter Response to Square Wave
*
.OPT NOPAGE NOBIAS
V1 101 0 SIN(0 1 800)
V3 102 101 SIN(0 ???? ????) ; Enter the amplitudes and frequencies
V5 1 102 SIN(0 ???? ????) ; of the third and fifth harmonic
; terms.
R1 ; Enter the device statements for the
R2 ; Butterworth filter circuit.
R3
C1
C2
E1
R4
R5
R6
C3
C4
E2
.TRAN ; Complete the .TRAN command for an
; analysis over a 5-millisecond period.
.PROBE
.END