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Filter Design (2)

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)

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  1. Filter Design (2) Jack Ou ES590

  2. 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

  3. Low Pass Filter Design Requirement • fc=1 MHz • Attenuation of 9 dB at 2 MHz. • RS=50 Ohms • RL=25 Ohms

  4. Determine the number of elements in the filter (Same as before) 9 dB of attenuation at f/fc of 2.

  5. Use a Low Pass Prototype Value for RS≠RL

  6. Comparison: RS=RL

  7. Frequency and Impedance Scaling

  8. Matlab Calculation

  9. Low Frequency Response

  10. 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.

  11. 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

  12. Comparison of a third order Passband Filter 3 dB of passband ripples and 10 dB improvement in attenuation

  13. 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)

  14. 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

  15. 0.1 dB Attenuation Chart

  16. 0.1 dB, n=2, Chebyshev

  17. Matlab Calculation

  18. Chbysehv, 0.1 dB Ripple, LPF ripple

  19. Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same.

  20. 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.

  21. Chebyshev, 5th Order, 0.1 dB Ripple

  22. Effect of Limited Inductor Quality Factor Assume each inductor has a quality factor of 10.

  23. Minimum Required Q

  24. Phase of ChebyshevBandpass Filter Phase is not very linear during the passband! You can get a lot of distortion!

  25. Bessel Filter • Bessel Filter is designed to achieve linear phase at the expense of limited selectivity!

  26. Low Pass Filter Design Requirement • fc=1 MHz • Attenuation of 9 dB at 2 MHz. • RS=50 Ohms • RL=25 Ohms

  27. Attenuation Possible to achieve 9dB

  28. Bessel LPF Prototype Elementary Value

  29. Matlab Calculation

  30. Bessel LPF 6.8 dB of attenuation at f/fc=2

  31. Phase of Bessel LPF (n=2)

  32. Genesys • BPF Design Example

  33. Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same.

  34. 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.

  35. Start Geneysis Select Passive Filter Start Genesys

  36. Filter Properties

  37. Comparison Synthesized Via Genesis Synthesized using Charts

  38. Change Settings

  39. QL=50, QC=100

  40. QL=10, QC=100

  41. Export Schematic to ADS (Not sure. ADS project is open)

  42. Tune • You can also fine-tune the value of a component and see how it changes the filter response

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