filter
The following describes filter types, what they do and how they perform. Along with definitions and detailed graphs, we are hopeful this information is both useful and informative.
Filter Types
Monolithic Crystal Filters
2 Quartz resonator internally coupled utilizing piezoelectric effect.
Discrete Crystal Filter
Single quartz resonator with external components utilizing the piezoelectric effect.
Notch filters
Crystal or Discrete component filter that passes all frequencies except those in a stop band centered on a center frequency. High Pass Filters
Discrete component filter that passes high frequency but alternates frequencies lower then the cut off frequency. Low Pass Filters
Discrete component filter that passes low frequency signals but alternates signals with frequencies higher then the cut off frequency.
Filter Designs
Chebyshev
The transfer function of the filter is derived from a chebychev equal ripple function in the passband only. These filters offer performance between that of Elliptic function filters and Butterworth filters. For the majority of applications, this is the preferred filter type since they offer improved selectivity, and the networks obtained by this approximation are the most easily realized.
Butterworth
The transfer function of the filter offers maximally flat amplitude. Selectivity is better then Gaussian or Bessel filters, but at the expense of delay and phase linearity. For most bandpass designs, the VSWR at center frequency is extremely good. Butterworth filters are usually the least sensitive to changes in element values.
Bessel/Linear Phase
The transfer function of the filter is derived from a Bessel polynomial. It produces filter with a flat delay around center frequency. The more poles used, the wider the flat region extends. The roll-off rate is poor. This type of filter is close to a Gaussian filter. It has poor VSWR and loses its maximally flat delay
Filter Types
Monolithic Crystal Filters
2 Quartz resonator internally coupled utilizing piezoelectric effect.
Discrete Crystal Filter
Single quartz resonator with external components utilizing the piezoelectric effect.
Notch filters
Crystal or Discrete component filter that passes all frequencies except those in a stop band centered on a center frequency. High Pass Filters
Discrete component filter that passes high frequency but alternates frequencies lower then the cut off frequency. Low Pass Filters
Discrete component filter that passes low frequency signals but alternates signals with frequencies higher then the cut off frequency.
Filter Designs
Chebyshev
The transfer function of the filter is derived from a chebychev equal ripple function in the passband only. These filters offer performance between that of Elliptic function filters and Butterworth filters. For the majority of applications, this is the preferred filter type since they offer improved selectivity, and the networks obtained by this approximation are the most easily realized.
Butterworth
The transfer function of the filter offers maximally flat amplitude. Selectivity is better then Gaussian or Bessel filters, but at the expense of delay and phase linearity. For most bandpass designs, the VSWR at center frequency is extremely good. Butterworth filters are usually the least sensitive to changes in element values.
Bessel/Linear Phase
The transfer function of the filter is derived from a Bessel polynomial. It produces filter with a flat delay around center frequency. The more poles used, the wider the flat region extends. The roll-off rate is poor. This type of filter is close to a Gaussian filter. It has poor VSWR and loses its maximally flat delay