Data Sheet

LJ1269HC
Rev1.0 Page 22 Web: www.ljelect.com
3.4 Receiver Description
The LJ1269HC features a digital receiver with the analog to digital conversion process being performed directly following the
LNA-Mixers block. The zero-IF receiver is able to handle (G)FSK and (G)MSK modulation. ASK and OOK modulation is,
however, demodulated by a low-IF architecture. All the filtering, demodulation, gain control, synchronization and packet
handling is performed digitally, which allows a very wide range of bit rates and frequency deviations to be selected. The receiver
is also capable of automatic gain calibration in order to improve precision on RSSI measurements.
Block Diagram
Figure 6. Receiver Block Diagram
The following sections give a brief description of each of the receiver blocks.
3.4.1. LNA - Single to Differential Buffer
The LNA uses a common-gate topology, which allows for a flat characteristic over the whole frequency range. It is designed to
have an input impedance of 50 Ohms or 200 Ohms (as selected with bit LnaZin in RegLna), and the parasitic capacitance at the
LNA input port is cancelled with the external RF choke. A single to differential buffer is implemented to improve the second order
linearity of the receiver.
The LNA gain, including the single-to-differential buffer, is programmable over a 48 dB dynamic range, and control is either
manual or automatic with the embedded AGC function.
Note In the specific case where the LNA gain is manually set by the user, the receiver will not be able to properly handle FSK
signals with a modulation index smaller than 2 at an input power greater than the 1dB compression point, tabulated in section
Table 12 LNA Gain Settings
LnaGainSelect
LNA Gain
Gain Setting
000
Any of the below, set by the AGC loop
-
001
Max gain
G1
010
Max gain - 6 dB
G2
011
Max gain - 12 dB
G3
100
Max gain - 24 dB
G4
101
Max gain - 36 dB
G5
110
Max gain - 48 dB
G6
111
Reserved
-
Sub GHz FSK/OOK Transceiver Module DATASHEET