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Filter Design (2) Jack Ou ES590 Slide 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 Slide 3 Low Pass Filter Design Requirement f c =1 MHz Attenuation of 9 dB at 2 MHz. RS=50 Ohms RL=25 Ohms Slide 4 Determine the number of elements in the filter 9 dB of attenuation at f/f c of 2. (Same as before) Slide 5 Use a Low Pass Prototype Value for RSRL Slide 6 Comparison: RS=RL Slide 7 Frequency and Impedance Scaling Slide 8 Matlab Calculation Slide 9 Low Frequency Response Slide 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. Slide 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 Slide 12 Comparison of a third order Passband Filter 3 dB of passband ripples and 10 dB improvement in attenuation Slide 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) Slide 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 Slide 15 0.1 dB Attenuation Chart Slide 16 0.1 dB, n=2, Chebyshev Slide 17 Matlab Calculation Slide 18 Chbysehv, 0.1 dB Ripple, LPF ripple Slide 19 Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same. Slide 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. Slide 21 Chebyshev, 5 th Order, 0.1 dB Ripple Slide 22 Slide 23 Effect of Limited Inductor Quality Factor Assume each inductor has a quality factor of 10. Slide 24 Minimum Required Q Slide 25 Phase of Chebyshev Bandpass Filter Phase is not very linear during the passband! You can get a lot of distortion! Slide 26 Bessel Filter Bessel Filter is designed to achieve linear phase at the expense of limited selectivity! Slide 27 Low Pass Filter Design Requirement f c =1 MHz Attenuation of 9 dB at 2 MHz. RS=50 Ohms RL=25 Ohms Slide 28 Attenuation Possible to achieve 9dB Slide 29 Bessel LPF Prototype Elementary Value Slide 30 Matlab Calculation Slide 31 Bessel LPF 6.8 dB of attenuation at f/fc=2 Slide 32 Phase of Bessel LPF (n=2) Slide 33 Genesys BPF Design Example Slide 34 Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same. Slide 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. Slide 36 Start Geneysis Start Genesys Select Passive Filter Slide 37 Filter Properties Slide 38 Comparison Synthesized Via Genesis Synthesized using Charts Slide 39 Change Settings Slide 40 Q L =50, Q C =100 Slide 41 Q L =10, Q C =100 Slide 42 Export Schematic to ADS (Not sure. ADS project is open) Slide 43 Tune You can also fine-tune the value of a component and see how it changes the filter response