Report

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 • Filter Synthesis via Genesis Low Pass Filter Design Requirement • • • • fc=1 MHz Attenuation of 9 dB at 2 MHz. RS=50 Ohms RL=25 Ohms Determine the number of elements in the filter (Same as before) 9 dB of attenuation at f/fc of 2. Use a Low Pass Prototype Value for RS≠RL Comparison: RS=RL Frequency and Impedance Scaling Matlab Calculation Low Frequency Response 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. 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 Comparison of a third order Passband Filter 3 dB of passband ripples and 10 dB improvement in attenuation 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) 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 0.1 dB Attenuation Chart 0.1 dB, n=2, Chebyshev Matlab Calculation Chbysehv, 0.1 dB Ripple, LPF ripple Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same. 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. Chebyshev, 5th Order, 0.1 dB Ripple Effect of Limited Inductor Quality Factor Assume each inductor has a quality factor of 10. Minimum Required Q Phase of Chebyshev Bandpass Filter Phase is not very linear during the passband! You can get a lot of distortion! Bessel Filter • Bessel Filter is designed to achieve linear phase at the expense of limited selectivity! Low Pass Filter Design Requirement • • • • fc=1 MHz Attenuation of 9 dB at 2 MHz. RS=50 Ohms RL=25 Ohms Attenuation Possible to achieve 9dB Bessel LPF Prototype Elementary Value Matlab Calculation Bessel LPF 6.8 dB of attenuation at f/fc=2 Phase of Bessel LPF (n=2) Genesys • BPF Design Example Typical Bandpass Specifications When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same. 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. Start Geneysis Start Genesys Select Passive Filter Filter Properties Comparison Synthesized Via Genesis Synthesized using Charts Change Settings QL=50, QC=100 QL=10, QC=100 Export Schematic to ADS (Not sure. ADS project is open) Tune • You can also fine-tune the value of a component and see how it changes the filter response