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Unformatted text preview: 1 1 Summary of Lecture #26 10/26/09 Analog filters What arfe filters for? Filter type by freq. characteristic: LP, HP, BP and BR filters Filter type by key components Filter order and roll off rate Realization of LP filters, examples Transformation from LP to HP, BP and BR Frequency and magnitude scaling +- +- V in (s) V out (s) s-domain circuit +- +- v in (t) v out (t) time-domain circuit 2 What are analog filters for? Frequency selectivity, i.e., to pass or block a frequency band To maximize power transfer from source to load To minimize reflection and interference caused by impedance mismatch Classification by frequency characteristic Low pass filters (LP) High pass filters (HP) Band pass filters (BP) Band rejection filters (BR) Types of analog filters by key components RLC filters Operational amplifier RC filters (op amp active RC filters) Switched-capacitor (SC) filters Operational transconductance amplifier (OTA) filters Current-conveyor (CC) filters Microwave filters Electromechanical filters Crystal filters RLC filters Made of passive elements: resistors, capacitors, and inductors (coils and transformers) No power supply is required. No signal distortion Practical from audio frequencies up to a few hundred MHz Shortcomings Significant pass band loss Inductors are required. Bulky and heavy at low frequencies Active RC filters Made of resistors, capacitors and active IC components (op. amp.) No inductor A power supply is required. Practical from 0.1 Hz to 500 kHz Size and weight advantage Compatible with planar IC technology Shortcomings A power supply is required. Output signal may be distorted if the input signal is too large. Possibly noisy 6 V in V out + _ + _ 1/(j C) R R V in V out + _ + _ 1/(j C) V in V out + _ + _ j L R V in V out + _ + _ R j L Low pass filters High pass filters Band pass filters Band rejection filters Examples of RLC filters 2 7 Examples of low pass and high pass filters- 20 dB/dec (first order)- 40 dB/dec (2nd order) +20 dB/dec (first order) + 40 dB/dec (2nd order) out in V (s) 1 H(s) V (s) 1 RCs = = + 1 RCs 3 ) RCs ( 1 ) s ( H 2 + + = ) L / R ( s s ) s ( H + = 2 2 2 ) L R ( s L R 3 s s ) s ( H + + = 8 Examples of band pass filters...
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