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LMX2240M データシート(PDF) 4 Page - National Semiconductor (TI) |
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LMX2240M データシート(HTML) 4 Page - National Semiconductor (TI) |
4 / 12 page Typical Application Block Diagram TLW11755 – 3 Functional Description OVERVIEW The LMX2240 IF demodulator is a low power IF processor that includes a frequency discriminator an IF hard limiting amplifier and a received signal strength indicator (RSSI) The LMX2240 is capable of differentially demodulating an FM or AM signal with as high an IF as 150 MHz avoiding a costly second down-conversion The RSSI output can be used for time gated channel measurements required in TDMA and other systems Other features include high re- ceiver sensitivity and a power down mode to allow for stand- by operation THE LIMITING AMPLIFIER The limiting amplifier has a typical gain of 70 dB and a sen- sitivity of about b75 dBm This allows it to be used in the DECT system with 20 dB net RF gain in front of it to achieve a sensitivity of b95 dBm The limiter is a five stage amplifier with internal compensation at each stage to ensure stability Two external compensation capacitors are also required to further enhance stability The input to the limiter is a relative- ly low impedance to allow easy matching to typical IF sur- face acoustic wave (SAW) filters The output of the limiter is connected off chip to an external quadrature tank circuit as well as connected internally to the discriminator (mixer) The output impedance of the limiter is 250X (typical) THE RECEIVED SIGNAL STRENGTH INDICATOR (RSSI) The RSSI circuit has a range of 70 dB Its output voltage is proportional to the logarithm of the input signal level The RSSI circuit has a sensitivity of b82 dBm The output volt- age of the circuit ranges from 05V to 15V typically THE FREQUENCY DISCRIMINATOR The frequency discriminator is a Gilbert cell mixer that re- quires an external tank circuit to create a 90 phase shift at the desired frequency The output of this circuit is centered at 15V by an internal level shifting circuit and a mid-range voltage (at 15V) is also provided The sensitivity of the dis- criminator to phase inaccuracies is 55 mVdegree (see Ap- plications Information) This means that for a phase imbal- ance of 10 the received eye diagram will be shifted by about 55 mV off of the 15V mid-range voltage For the typi- cal case this amounts to about 10% of the output eye dia- gram (for 400 mVPP output) 4 |
同様の部品番号 - LMX2240M |
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同様の説明 - LMX2240M |
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