low pass filters in detail Low Pass Filters RC Low Pass Filter Critical or cutoff frequency Response curve Cutoff frequency of RC LPF RL Low Pass Filter Cutoff Frequency of RL LPF Phase Response in Low Pass Filter

1. LOW PASS
FILTERS
KUNWAR TOUSEEF
L1F12BSEE0120

2. Contents
• Introduction of Filters
• Low Pass Filters
• RC Low Pass Filter
• Critical or cutoff frequency
• Response curve
• Cutoff frequency of RC LPF
• RL Low Pass Filter
• Cutoff Frequency of RL LPF
• Phase Response in Low Pass Filter

3. Introduction of Filters
• Basically, an electrical filter is a circuit that can be
designed to modify, reshape or reject all unwanted
frequencies of an electrical signal and accept or
pass only those signals wanted by the circuits
designer. In other words they "filter-out" unwanted
signals and an ideal filter will separate and pass
sinusoidal input signals based upon their
frequency.

4. Low Pass Filter
• A low-pass filter is a filter that allows signals with low
frequencies to pass from input to output while rejecting higher
frequencies.
• A Low Pass Filter can be a combination of capacitance,
inductance or resistance intended to produce high attenuation
above a specified frequency and little or no attenuation below
that frequency.

5. RC Low Pass Filter
• A simple RC Low Pass Filter or LPF, can be easily made by
connecting together in series a single Resistor with a single
Capacitor. In this type of filter arrangement the input signal
(Vin ) is applied to the series combination (both the Resistor
and Capacitor together) but the output signal (Vout ) is taken
across the capacitor only

7. Critical or Cutoff frequency
• The frequency at which the transition occurs and the filter’s
output is 70.7% of input is called the critical or "cutoff"
frequency.

8. Response curve of Low Pass
Filter

9. Cutoff frequency of RC LPF
• Xc =R
1/2πfc =R
fc =1/2πRc
At the cutoff frequency the output voltge magnitude is
Vout=Vin x Xc/√R^2+Xc^2

10. RL Low Pass Filter
• It is made by connecting a inductor and a resistor in
series and output is taken across the resistor.

11. Cutoff Frequency of RL LPF
XL=R
2πfcL =R
fc =1/2π(L/R)

12. Phase Response in Low Pass
Filter
• Both the RC and RL low pass filter act as lag
network.