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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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