User Guide

NPM-10 (3595)

System Module CC Technical Documentation

Receiver

The receiver is a dualband, direct-conversion, linear receiver. The received RF signal is

routed from the antenna to the RX/TX switch. The RX/TX switch performs both the

switching between receive – transmit routing of the antenna signals as well as the

selection of the band to be used.

The RX signal is routed from the RX/TX switch to the RX bandpass filter. The filter input is

single-ended and the output is balanced in order to exploit the balanced nature of the RF

ASIC. The band-limited signal is amplified in the internal LNA and the pre-gain amplifier

before being converted to a BB signal in the passive mixer.

The gain characteristic of the BB amplifier is an amplifier with a maximum gain of 80 dB

with an AGC range of 72 dB in 6 dB steps.

The receiver selectivity for out-of-band signals is defined by the RF front-end SAW filter.

The receiver ability to withstand large out-of-band signals is defined by the RF SAW

filter and the large signal behavior of the LNA – pregain and mixer.

The inband selectivity is define by the channel filters in Mjoelner, and the in-band large

signal behavior is a combination of the RF front-end and the BB amplifier large signal

behavior.

AGC

Since the receiver is a linear type, the AGC must keep the BB level from the receiver

within a certain range in order to stay within the dynamic range for the BB, even during

fading. The AGC has to be set before each received burst with pre-monitoring or without

pre-monitoring. In pre-monitoring, the receiver is switched on approximately 130 µs

before the burst begins. DSP measures the received signal level and adjusts AGC

amplifiers via the serial bus.

RSSI must be measured accurately on range -48 dBm to -110 dBm. After the -48 dBm

level, MS reports to base station the same reading.

The AGC is a combination of gain-controlled elements at both RF and BB frequencies.

It is the LNA in RF that is used as an AGC element with one step. The AGC step size of the

LNA will have different values between 900 MHz and 1800 MHz, as well as across the

band.

In BB the AGC has 12 steps, a combination of DCN_1 and AGC, with a resolution of

~6 dB, giving a total BB AGC range of 72 dB.