Berkeley ELENG 240A - Lecture 19: High-Speed Filter Design

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EECS240 – Spring 2009Lecture 19: High-Speed Filter DesignElad AlonDept. of EECSEECS240 Lecture 19 2Link Channels and ISI0 2 4 6 8 10-60-50-40-30-20-100frequency [GHz]Attenuation [dB]9" FR4, via stub26" FR4,via stub26" FR49" FR4• 20-30dB loss at 3GHz• How bad is that?• Two related issues:• (1) Noise and min. signal amplitude• (2) IntersymbolinterferenceEECS240 Lecture 19 3Inter-symbol interference (ISI)• Channel is low pass• Short TX pulses get spread out0 1 2 300.20.40.60.81nspulse responseTsymbol=160psEECS240 Lecture 19 4Impact of ISI• Middle sample is corrupted by 0.2 trailing ISI (from previous symbol) and 0.1 leading ISI (from next symbol) • Total ISI: 0.3 total ISI• Middle symbol incorrectly detected0 2 4 6 8 10 12 14 16 1800.20.40.60.81Symbol timeAmplitudeError!EECS240 Lecture 19 5Equalization• ISI is proportional to TX swing• Generally can’t just boost signal to overcome it• Solution: Equalization• If channel applies filter H(s)• Pass the signal through another filter H-1(s)EECS240 Lecture 19 6Equalization cont’d• Link channel basically low-pass• Equalizer boosts high frequency, attenuates low frequencyEECS240 Lecture 19 7Equalizer RequirementsEECS240 Lecture 19 8Equalizer Requirements cont’dEECS240 Lecture 19 9Equalizer Options and LimitationsEECS240 Lecture 19 10RX EqualizerEECS240 Lecture 19 11RX Equalizer ImplementationsEECS240 Lecture 19 12RX Equalizer ImplementationsEECS240 Lecture 19 13RX Equalizer ImplementationsEECS240 Lecture 19 14RX Equalizer ImplementationsEECS240 Lecture 19 15ProgrammabilityEECS240 Lecture 19 16Aside: Switched Cap. ResistorEECS240 Lecture 19 17Aside: Switched Cap Low-Pass


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Berkeley ELENG 240A - Lecture 19: High-Speed Filter Design

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