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4.4 Receivers
4.4.1 Receiver: GSM900/1800 Diplexer > Filter > LNA > Mixer
From the antenna switch up to the IF-Mixer, the GSM1800 receiver circuit
consists of:
a) a ceramic front end filter (Z555)
b) a LNA (Low Noise Amplifier D550)
c) and a subsequent discrete distortion LC-high-pass-filter.
For GSM900 the signal flow is as follows: From the antenna switch, via a SAW filter
(Z556), through the LNA (D550) and a discrete distortion LC-low-pass-filter to the
IF-Mixer..
The amplification of both LNA´s is approx. 20dB with a matched 50 ohm output.
The LNA is switched "On" with the signal
For switching between GSM1800 and GSM900 the signal
the (SMARTI
pin
37).
The signal
LNAG
(SMARTI
with
LNAG
"active", the LNA reduces the incoming signal in one step by 20dB
The non-symmetrical LNA output is connected to the IF mixer via a discrete
balancing and adaptation circuit. This circuit converts the asymmetrical
signal into a symmetrical signal.
The required voltage
VCC2_8
V1.0
A35-A36-A40
LNAON
(SMARTI
pin
33) is in use, if the received signal level is too high.
is provided by
N430
4413
4414
Page 12 of 38
Company Confidential
pin
36).
BSW
is generated from
4412
Notes
4411
ICM MP CC ST
09/01
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