filters Flashcards
what is a low pass filter
allows signals with lower frequencies to pass whilst rejecting higher frequencies
what is a passband
the range of frequencies passed by a filter within a specified limit
what is the cut off frequency / critical frequency
(-3db)
the frequency at which the output voltage is 70.7% of the max
- can be constructed from either RC or RL components
how is cut off frequency calculated in a RC circuit
fc = 1 / 2 x pie x R x C
how is cut off frequency calculated in a RL circuit
fc = 1 / 2 x pie x (L/R)
low pass RL & RC circuits both are log networks at cut off freqeuncies. What is their phase shift angle
45º
what is decibels
the ratio between 2 physical quantities
10log (Pout/Pin)
Pout - power output
Pin - power input
when measuring voltage across the same impedance, how is decibels calculated
20log (Vout/Vin)
Vout - voltage ouput
Vin - voltage input
what is the roll of response
when output drops from 0 to -3db at critical frequency and then continues to drop off at a fixed rate
what is roll off rate of basic RC/RL filters
-20db per decade
what is a high pass filter
allows signals with a high frequency to pass whilst rejecting lower frequencies
what is the phase shift angle for high pass RC & RL circuits
they are lead networks so +45º
what is bandwidth
where the frequencies drop to 70.0% of max on bell curve
what is resonant frequency
Vmax
what is Fc1 & Fc2
Fc1 - lower cut off point
Fc2 - higher cut off point
how is resonant frequency calculated
fr = 1 / 2 x pie x (square root LC)
L - inductance
C - capacitance
how is band width calculated
fr / Q
Q = XL/ wR
Fc2 - Fc1
Q = quality factor
how is fc1 calculated
fr - bw/2
how is fc2 calculated
fr + bw/2
