AT86RF211S Datasheet | Atmel

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 k Hz AT86RF211S FSK Transceiver for ISM Radio Applications Application Note 2. From Analog to Digital 2.1 Demodulation .. 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 k Hz - 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 k Hz Vcc 1st filtering stage FRF 2nd filtering stage Discriminator F V Converter L01 L02 10.7 MHz bandwidth = hundreds of k Hz 455 k Hz bandwidth = tens of k Hz SYNCHRONOUS RESHAPED CMOS LEVELS Vcc DATAMSG GND Data slicer threshold DATACLK CLOCK RECOVERY Embedded function The AT86RF211S discriminator is analog: the output voltage is proportional to the input frequency. It was particularly designed to accept a very long sequence of “zeros” or “ones” (i.e. a constant input frequency). This is not the case for all receivers (in other words, with some transceivers it is necessary to use DC-free data encoding). Figure 2-2. Classic Discriminator without DC...