AT86RF211S

Data Demodulation and Crystal Selection for the AT86RF211S 1. Introduction This document gives an overview of the receiver chain of the AT86RF211S and its associated embedded features: Discriminator: Demodulation of the RF signal (principle, measurement/tuning of output voltage) Data slicer:From analog to digital world (different modes of functioning, how to set up the data slicer threshold) It also emphasizes the new possibilities of the AT86RF211S Selection of lower cost crystal Data rate up to 128 kbps Frequency deviation wider than ±100 kHz AT86RF211S FSK Transceiver for ISM Radio Applications Application Note 2. From Analog to Digital 2.1 Demodulation www.DataSheet4U.com 2.1.1 Principle The FSK modulation used by the AT86RF211S consists in coding each bit as follows: “0”: transmission of an RF signal at a frequency F0 “1”: transmission of an RF signal at a frequency F1 The channel frequency (or carrier) is the middle frequency Fc = (F0 + F1)/2 F1 - Fc = Fc - F0 is called the frequency deviation The receiver therefore has the overall task to: Down-convert the signal at lower frequencies (for filtering purposes): 10.7 MHz and 455 kHz Convert the frequencies into voltages (= discriminator) Make a decision to separate “0” from “1” levels (= data slicer) Rev. 5418A–WIRE–04/05 Figure 2-1. Principle of Demodulation Signal down-converted at 10.7 MHz 2 nd down-conversion at 455 kHz Vcc 1st filtering stage FRF 2nd filtering stage Discriminator ...