AT86RF211S Application Note
Figure 2-3. AT86RF211: Discriminator with DC Ability
0 1 0 1 10 1
Standard/Narrowband Modes of the Discriminator
Since the output swing of the discriminator is proportional to the input frequency deviation,
small frequency deviations (used in narrowband applications) lead to smaller peak-to-peak
values of discriminator output. For this reason, the discriminator’s gain can be selected. The
AT86RF211S features four different gains – NDB, SDB, MDB and WDB – where NDB and
SDB are fully compatible with the AT86RF211.
The slope of the demodulator is:
• Standard Discriminator Bandwidth mode: 14 mV/kHz at 2.4V (+5 mV per volt of power
• Narrow Discriminator Bandwidth mode: 28 mV/kHz at 2.4V (+10 mV per volt of power
• Medium Discriminator Bandwidth mode: 9 mV/kHz at 2.4V (+4 mV per volt of power
• Wide Discriminator Bandwidth mode: 5.5 mV/kHz at 2.4V (+2 mV per volt of power supply)
In order for the system to operate properly, the basic requirements are the following:
• The frequency deviation must be in accordance with the data rate (the higher the data rate,
the larger the frequency deviation).
• The down-converted frequencies must remain within the IF filters over the entire operating
conditions (temperature range, ageing), particularly when a narrow IF2 filter is used.
The typical values are:
=> 10.7 MHz filter: ±50 to ±150 kHz (ceramic filter)
=> optional 455 kHz second IF filter: ±2 to ±17.5 kHz (ceramic filter).
• The output of the discriminator must not exceed the maximum allowed voltage range. The
level on DISCOUT depends on several parameters: the received signal frequency, the
receiver local oscillator, the amplifier offsets, etc.
• The temperature drifts of the crystal are often given in ppm (parts per million) over a given
temperature range. 1 ppm is 0.9 kHz at 900 MHz and 0.4 kHz at 400 MHz, with a 10.245