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Abridged Glossary of Filter Terminology
Attenuation
Loss of signal through a filter during transmission; measured in decibels (dB).
Bandwidth
The width of the pass band of a
band-pass
filter
is the frequency difference
between
lower and
upper corner
frequencies,
such as 1 or 3 db
points.
Center Frequency
The arithmetic mean frequency
is called
center
frequency (F0).
It is calculated using
the
1 or
3 dB relative band
edges (F1 and F2)
as
( )
2
1 F0 = F1+F2/2,
where F1 and F2 are
lower and
upper frequencies
at which
a particular signal
attenuation occurs (see Figure 3).
Cutoff Frequency (Fc)
The cutoff frequency (Fc) is
the upper
passband edge in
low-pass filters or the
lower
passband edge in high-pass
filters.
A .Uvitech normally uses the
point at
which the
attenuation
has relative 1 or 3 dB loss.
This
point is usually called the relative
1 or 3 dB
point (Figures 1 and 2).
High-Pass Filter
A filter that passes high frequencies
and rejects
low frequencies.
Input Impedance
The impedance measured at the input
terminal
of a filter when it is properly
terminated at its
output.
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Input Impedance
The impedance measured at the input terminal
of a filter when it is properly terminated at its
output.
Insertion Loss
The loss of signal caused by a filter being
inserted into a circuit and measured in decibels.
In general, it is the ratio of power delivered to
the load with a filter in the circuit to the power
in the load if a perfect lossless matching
transformer replaced the filter.
A .Uvitech maintains insertion loss values from DC to 90% of center frequency for low pass filters, and from
110% of center frequency to maximum spurious-free frequency for high-pass filters (Figures 1 and
2) and at center frequency, or for the full pass band for band-pass filters.
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Filter Response
A .Uvitech Ltd. designs and manufactures filters with various amplitude shapes, phase, and group
delay response. The majority of the filters are designed to one of the following responses:
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- Butterworth Response. Maximum flat pass band insertion loss and monotonic stop bands. Pass
band is defined as the 3 dB relative insertion loss.
- Chebyshev Response. Equal ripple insertion loss in the pass band, and monotonic stop bands.
Pass band insertion loss is defined as the relative 1 dB or 3 dB points.
- Generalized Chebyshev Response. Equal ripple insertion loss, and a single pole in each stop
band.
- Elliptic (Caver) Response. Equal ripple insertion loss in pass band, and equal minimum
attenuation in stop bands.
- Gaussian Response. Compromise between high rejection and linear phase response.
- Bessel Response. Optimized phase linearity response in pass band, maintaining a constant
group delay. The rejection in stop bands is however sacrificed.
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