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5418A–WIRE–04/05

AT86RF211S Application Note

• The crystal specifications in this document (ageing and temperature drifts) are given for the

868 to 915 MHz bands. For an application in the 400 MHz to 480 MHz band, these

specifications can be relaxed and multiplied by 2.

• These specifications (temperature and ageing) include the Tx and Rx sides: the overall drift

must meet these requirements.

• Thanks to the high resolution of the AT86RF211S synthesizer (typically 200 Hz) a given

accuracy can be achieved by software: a small shift of the frequency (made by software) is

able to compensate a temperature or ageing drift with no additional hardware cost.

2.2

Data Slicing

Once the frequency has been converted into a voltage, a decision must be made to identify

the “0” and “1” levels and convert them into CMOS levels. This is achieved thanks to a com-

parator. The AT86RF211S offers two data-slicing possibilities.

Figure 2-4.

Data Slicing

With the AT86RF211S, a hold is possible on the SKFILT capacitor. This helps to maintain the

average value of the signal captured without any discharge during reception of the message.

2.2.1

External Mode Comparing The Signal to its Average Value

A first possibility consists in comparing the signal to its own average value: a capacitor on

SKFILT (pin 25) is charged to the average value of the signal.

Demodulated signal on DISCOUT pin

Data slicer threshold set on SKFILT pin

Data slicer threshold level set by internal DAC (DSREF)

Data slicing

options