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Filter Design (2). Jack Ou ES590. Last Time Outline. Butterworth LPF Design LPF to HPF Conversion LPF to BPF Conversion LPF to BRF Conversion General Cases Dual Networks RL≠RS Other Filters Chebyshev filter Bandpass Design Example Bessel filter Bandpass Design Example
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Filter Design (2) Jack Ou ES590
Last Time Outline • Butterworth LPF Design • LPF to HPF Conversion • LPF to BPF Conversion • LPF to BRF Conversion • General Cases • Dual Networks • RL≠RS • Other Filters • Chebyshev filter • Bandpass Design Example • Bessel filter • Bandpass Design Example • Filter Synthesis via Genesis
Low Pass Filter Design Requirement • fc=1 MHz • Attenuation of 9 dB at 2 MHz. • RS=50 Ohms • RL=25 Ohms
Determine the number of elements in the filter (Same as before) 9 dB of attenuation at f/fc of 2.
Comments about Butterworth Filter • A medium –Q filter that is used in designs that require the amplitude response of the filter to be as flat as possible. • The Butterworth response is the flattest passband response available and contains no ripples.
Chebyshev Response • Chebyshev filter is a high-Q filter that is used when : • (1) a steeper initial descent into the passband is required • (2) the passband response is no longer required to be flat
Comparison of a third order Passband Filter 3 dB of passband ripples and 10 dB improvement in attenuation
Design Methodology • Even though attenuation can be calculated analytically, we will use the graphical method. • Even order Chebyshev filters can not have equal termination (RS≠RL)
Low Pass Filter Design Requirement • fc=1 MHz • Attenuation of 9 dB at 2 MHz. • RS=50 Ohms • RL=25 Ohms • Less than 0.1 dB of Ripple • Design it with a Chebychev Filter
Chbysehv, 0.1 dB Ripple, LPF ripple
Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same.
Butterworth Vs. Chebyshev Butterworth: n=4, 40 dB Chebyshev: n=4, 48 dB, but RS≠RL We have to settle for n=5, 62 dB.
Effect of Limited Inductor Quality Factor Assume each inductor has a quality factor of 10.
Phase of ChebyshevBandpass Filter Phase is not very linear during the passband! You can get a lot of distortion!
Bessel Filter • Bessel Filter is designed to achieve linear phase at the expense of limited selectivity!
Low Pass Filter Design Requirement • fc=1 MHz • Attenuation of 9 dB at 2 MHz. • RS=50 Ohms • RL=25 Ohms
Attenuation Possible to achieve 9dB
Bessel LPF 6.8 dB of attenuation at f/fc=2
Genesys • BPF Design Example
Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same.
Butterworth Vs. Chebyshev Butterworth: n=4, 40 dB Chebyshev: n=4, 48 dB, but RS≠RL We have to settle for n=5, 62 dB.
Start Geneysis Select Passive Filter Start Genesys
Comparison Synthesized Via Genesis Synthesized using Charts
Export Schematic to ADS (Not sure. ADS project is open)
Tune • You can also fine-tune the value of a component and see how it changes the filter response