# 8.6.1. Low Pass Rc Filter¶

#r# This example shows a low-pass RC Filter.

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import math
import numpy as np
import matplotlib.pyplot as plt

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import PySpice.Logging.Logging as Logging
logger = Logging.setup_logging()

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from PySpice.Plot.BodeDiagram import bode_diagram
from PySpice.Spice.Netlist import Circuit
from PySpice.Unit import *

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#f# circuit_macros('low-pass-rc-filter.m4')

circuit = Circuit('Low-Pass RC Filter')

circuit.SinusoidalVoltageSource('input', 'in', circuit.gnd, amplitude=1@u_V)
R1 = circuit.R(1, 'in', 'out', 1@u_kΩ)
C1 = circuit.C(1, 'out', circuit.gnd, 1@u_uF)

#r# The break frequency is given by :math:f_c = \frac{1}{2 \pi R C}

break_frequency = 1 / (2 * math.pi * float(R1.resistance * C1.capacitance))
print("Break frequency = {:.1f} Hz".format(break_frequency))
#o#

simulator = circuit.simulator(temperature=25, nominal_temperature=25)
analysis = simulator.ac(start_frequency=1@u_Hz, stop_frequency=1@u_MHz, number_of_points=10,  variation='dec')
# print(analysis.out)

#r# We plot the Bode diagram.

figure, axes = plt.subplots(2, figsize=(20, 10))
plt.title("Bode Diagram of a Low-Pass RC Filter")
bode_diagram(axes=axes,
frequency=analysis.frequency,
gain=20*np.log10(np.absolute(analysis.out)),
phase=np.angle(analysis.out, deg=False),
marker='.',
color='blue',
linestyle='-',
)
for ax in axes:
ax.axvline(x=break_frequency, color='red')

plt.tight_layout()
plt.show()

#f# save_figure('figure', 'low-pass-rc-filter-bode-diagram.png')


This example shows a low-pass RC Filter.

import math
import numpy as np
import matplotlib.pyplot as plt

import PySpice.Logging.Logging as Logging
logger = Logging.setup_logging()

from PySpice.Plot.BodeDiagram import bode_diagram
from PySpice.Spice.Netlist import Circuit
from PySpice.Unit import *

circuit = Circuit('Low-Pass RC Filter')

circuit.SinusoidalVoltageSource('input', 'in', circuit.gnd, amplitude=1@u_V)
R1 = circuit.R(1, 'in', 'out', 1@u_kΩ)
C1 = circuit.C(1, 'out', circuit.gnd, 1@u_uF)


The break frequency is given by $$f_c = \frac{1}{2 \pi R C}$$

break_frequency = 1 / (2 * math.pi * float(R1.resistance * C1.capacitance))
print("Break frequency = {:.1f} Hz".format(break_frequency))

Break frequency = 159.2 Hz

simulator = circuit.simulator(temperature=25, nominal_temperature=25)
analysis = simulator.ac(start_frequency=1@u_Hz, stop_frequency=1@u_MHz, number_of_points=10,  variation='dec')
# print(analysis.out)


We plot the Bode diagram.

figure, axes = plt.subplots(2, figsize=(20, 10))
plt.title("Bode Diagram of a Low-Pass RC Filter")
bode_diagram(axes=axes,
frequency=analysis.frequency,
gain=20*np.log10(np.absolute(analysis.out)),
phase=np.angle(analysis.out, deg=False),
marker='.',
color='blue',
linestyle='-',
)
for ax in axes:
ax.axvline(x=break_frequency, color='red')

plt.tight_layout()
plt.show()