Tx Arch's8337_2008c

Tx Arch's8337_2008c - Transceiver Architectures 1 Analog...

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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 1 Transceiver Architectures
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 2 Transceiver Architectures ± Limited spectrum z Need coding/compression and efficient modulation schemes ± Need to avoid being overpowered by large neighboring interferes z Linearity ± Narrow band filtering/amplification z Filtering and down-conversion ± Small desired signal z Typically need 100dB of overall gain (a few micro volts) ± Criteria for selection z Complexity z Cost z Power z Number of external components z Time to market
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 3 Lowering Costs ± Lowering costs nearly synonymous with increased integration MTT, Aravind Loke and Fazal Ali , Fellow, IEEE, November 2002
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 4 Rx Architectures Classification ± One classification z Single IF Homodyne Zero-IF / direct conversion z Multiple IF Hetrodyne Super-hetrodyne ± The last IF frequency z Zero IF z Low IF ± Real or complex IF ± Where you sample & digitize
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 5 Radio Architectures Study ± Single-IF z Zero-IF (homodyne) z Low-IF ± Traditional multi-IF z Zero-IF (hetrodyne, super-hetrodyne) ± Complex frequencies ± Harley & Weaver architectures revisited ± Image-reject architectures ± Complex filters ± Modern multi-IF ± Other architecture issues ± WLAN examples
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 6 Narrow Bandwidth ± Rx ± Q-Requirements z IS-54 or IS-98 z Not feasible even with SAW devices z Tradeoff between loss and Q z Cannot vary center frequency of filter Adjacent Channels Desired Channel LNA BPF 30kHz centered @900MHz BPF 45kHz 60dB Q RF = 900 MHz 30 kHz = 3 × 10 4
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 7 Architectures ± Downconversion ± Filter Q requirements z At RF z AT IF (let IF = 10.7MHz) w lo w rf w rf LPF W rf -w lo W rf + w lo w IF =W rf lo Q RF = 900 MHz 30 kHz = 3 × 10 4 Q IF = 10.7 MHz 30 kHz 357
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 8 Down Conversion Architectures ± Mixers are usually lossy and not optimized for low noise z Therefore, add a low noise amplifier (LNA) in front ± Image problem z Local oscillator (LO) and intermediate frequency (IF) selected because of image considerations z For hetrodyne systems bands symmetrically above and below the LO are down converted to the same frequency w lo w rf w rf LPF W rf -w lo W rf + w lo w IF =W rf lo LNA
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 9 Image Problem ± Image can be much larger than desired signal z Problem can be serious Image Desired LO IF
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 10 Image Rejection ± 1 method to handle image problem use image reject (IR) filter w lo w rf LNA IR Filter Image Desired LO IR FIlter W IF W IF
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 11
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Tx Arch's8337_2008c - Transceiver Architectures 1 Analog...

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