AT86RF211 datasheet(17/48 Pages) ATMEL

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AT86RF211

1942C–WIRE–06/02

The input RBW resistor controls the discriminator bandwidth. This bandwidth is selected

by CTRL1[6]. The default value is "standard discriminator BW". The slope of the discrim-

inator increases by 5 mV/kHz/V with V

CC andis 14mV at 2.4V.

Example:

CC = 3V implies +17 mV/kHz sensitivity for the demodulator

CC = 3.6V implies +20 mV/kHz sensitivity for the demodulator

Data Slicer

The analog signals at the output of the discriminator (DISCOUT, pin 27) are converted

into CMOS level data by a high resolution comparator called a Data Slicer.

The Data Slicer has a reference for its comparator which can be chosen thanks to

CTRL1[4]. The reference sets the comparison level of the comparator. One option is to

extract the average value of the demodulated signal on the SKFILT pin (25), this is the

external mode. The other option is to set an absolute value for this reference (internal

mode).

•

External mode:

The external mode uses the average value of the demodulated signal as the compari-

son level for the comparator. Thus there must be enough transitions in the message to

ensure that the average value remains between the "0" level and the "1" level. Manches-

ter encoding can be used in this mode as well as DC-free encoding schemes. The

choice for SKFILT capacitor is a trade-off between the maximum duration of a constant

bit (whatever "0" or "1") and the max allowed settling time to charge this capacitor after

powering up.

Note:

The SKFILT pin is in high impedance state during the "sleep" period of the Wake Up

mode, so that the level is kept constant and there is no need to charge again this tank.

•

Internal mode:

The internal mode uses the output of a DAC as the comparison level. Once this thres-

hold has been correctly set, an "absolute" data slicing of the demodulated signal is

possible: no need for DC-free modulation scheme (it is possible to send a "0" or "1"

infinitely).

Figure 21. Schematic of the Data Slicer

DATAMSG

100 k

Ω

DISCOUT

Vdd/2

SKFILT

DSIN

4 bits

Choice of internal or

external reference for

the data slicer

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