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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.

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Presentation on theme: "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."— Presentation transcript:

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 – RLRS Other Filters – Chebyshev filter – Bandpass Design Example – Bessel filter – Bandpass Design Example Filter Synthesis via Genesis

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

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

5 Use a Low Pass Prototype Value for RSRL

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 (RSRL)

14 Low Pass Filter Design Requirement f c =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 dBChebyshev: n=4, 48 dB, but R S R L We have to settle for n=5, 62 dB.

21 Chebyshev, 5 th Order, 0.1 dB Ripple

22

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 f c =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 dBChebyshev: n=4, 48 dB, but R S R L We have to settle for n=5, 62 dB.

36 Start Geneysis Start Genesys Select Passive Filter

37 Filter Properties

38 Comparison Synthesized Via Genesis Synthesized using Charts

39 Change Settings

40 Q L =50, Q C =100

41 Q L =10, Q C =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


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