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參數(shù)資料
| 型號： | LMX2240 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Crimp Tool for Power Connectors, Male; For Use With:Molex Pitch Sabre Terminals; Wire Size (AWG):18-14 |
| 中文描述： | 中頻接收機(jī) |
| 文件頁數(shù)： | 4/12頁 |
| 文件大小： | 208K |
| 代理商： | LMX2240 |
Typical Application Block Diagram
TL/W/11755–3
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
b
75 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
b
95 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 250
X
(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
b
82 dBm. The output volt-
age of the circuit ranges from 0.5V to 1.5V 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 1.5V by an internal level shifting circuit, and a mid-range
voltage (at 1.5V) is also provided. The sensitivity of the dis-
criminator to phase inaccuracies is 5.5 mV/degree (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 1.5V mid-range voltage. For the typi-
cal case, this amounts to about 10% of the output eye dia-
gram (for 400 mV
PP
output).
4
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相關(guān)代理商/技術(shù)參數(shù) |
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| LMX2240M | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Intermediate Frequency Receiver |
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| LMX2301TM | 制造商:Texas Instruments 功能描述: |
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| LMX2305 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:PLLatinumTM 550 MHz Frequency Synthesizer for RF Personal Communications |
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