RF69 datasheet(23/81 Pages) ETC2

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RF69

Page 23

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3.4. Receiver Description

The RF69 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.

3.4.1. Block Diagram

Rx Calibration

Reference

RFIO

From

PA1

LNA

Single to

Differential

Mixers



Modulators

Channel

Filter

Cancellation

Complex

Filter

CORDIC

Phase

Output

Module

Output

RSSI

FSK

Demodulator

OOK

Demodulator

Local

Oscillator

AFC

Bypassed

in FSK

AGC

Figure 7. Receiver Block Diagram

The following sections give a brief description of each of the receiver blocks.

3.4.2. 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 3.4.3.

Table 12 LNA Gain Settings

LnaGainSelect

LNA Gain

Gain Setting

000

Any of the below, set by the AGC loop

001

Max gain

010

Max gain - 6 dB

011

Max gain - 12 dB

100

Max gain - 24 dB

101

Max gain - 36 dB

110

Max gain - 48 dB

111

Reserved

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