1. Filter Design (2)
Jack Ou
ES590

2. Last Time Outline Butterworth LPF Design General Cases Other Filters
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
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

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

24. Minimum Required Q

25. Phase of Chebyshev Bandpass Filter
Phase is not very linear during the passband!
You can get a lot of distortion!

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

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

28. Attenuation
Possible to achieve 9dB

29. Bessel LPF Prototype Elementary Value

30. Matlab Calculation

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

32. Phase of Bessel LPF (n=2)

33. Genesys
BPF Design Example

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

35. 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.

36. Start Geneysis
Select Passive Filter
Start Genesys

37. Filter Properties

38. Comparison
Synthesized Via Genesis
Synthesized using Charts

39. Change Settings

40. QL=50, QC=100

41. QL=10, QC=100

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

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