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Review of Important AM Receiver Concepts

Review of Important AM Receiver Concepts. Receiver Sensitivity: P SB,MIN ( dBm ) - N EFF ( dBm ) > SNR MIN (dB) P SB,MIN ( dBm ) = P SENS ( dBm ) - 10log 10 (2/m 2 + 1) N EFF ( dBm ) = kT 0 B( dBm ) + NF(dB) + 3 dB (if no image rejection after first amp)

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Review of Important AM Receiver Concepts

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  1. Review of Important AM Receiver Concepts • Receiver Sensitivity: • PSB,MIN(dBm) - NEFF(dBm) > SNRMIN(dB) • PSB,MIN(dBm) = PSENS(dBm) - 10log10(2/m2 + 1) • NEFF(dBm) = kT0B(dBm) + NF(dB) • + 3 dB (if no image rejection after first amp) • PSENS(dBm) = kT0B(dBm) + NF(dB) + SNRMIN(dB) + 10log10(2/m2 + 1) + 3 dB (?) • Required detector power for undistorted demodulation: • (1-m)EC,DET > VD PSB,MIN

  2. Review of Important AM Receiver Concepts • Total Gain Required (RF and IF) • GMIN(dB) = PDET,MIN(dBm) – PSENS(dBm) • Image Rejection - Preselectors • fIM = fCH+ 2fIF (…depending upon high/low injection) • Worst Case – Highest channel frequency for Low Side Injection • Lowest channel frequency for High Side Injection • Adjacent Channel Rejection – IF Filters • Channel spacing includes guard band • Center Frequency is IF Frequency • Bandwith (B) extends to guard band edges • Required rejection must be exhibited at edge of adjacent channel guard band

  3. Build a Radio!! Frequency Range 161 – 174 Mhz (Land Mobile Band) Channel Spacing: 30 kHz, Guard Band: 5 kHz IF filter: crystal filter with Qu = 20,000 (want 40 dB adjacent channel rejection) Pre-selectors: LC filters with Qu= 180 (want 40 dB image rejection) Detector: VD = 0.2 v, RDC = 500 ohms Mixer: Conversion loss = 6 dB Want 1.5 uV sensitivity for ma = 0.7 (SNR = 12 dB) Design Tradeoff: The higher the IF frequency, the easier it is to get image rejection, but the harder it is to achieve adjacent channel rejection. • Tasks • Determine Pre-selector characteristics • Determine IF Frequency and filter characteristics • Determine Required Gain • Determine PSENS, noise figure/loss requirements • Determine PDET,MIN

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