at86rf211 ATMEL Corporation, at86rf211 Datasheet - Page 16

• Manufacturer Part Number: at86rf211
• Description: Fsk Transceiver For Ism Radio Applications
• Manufacturer: ATMEL Corporation

FSK Demodulator
16
AT86RF211
Figure 19. ADC Converter Input Selection
Note:
The ADC measuring the RSSI can be turned into voltage or discriminator output DC
level measurement.
Its structure is based on an oscillator:
Figure 20. Schematic of the FSK demodulator
The oscillator’s natural frequency is F
The signal at the output of the oscillator (point A) is proportional to the frequency differ-
ence between Fin and F
cycle (point B).Thereafter by low-pass filtering of the signal is obtained a mean voltage
of the signal (point C).
The architecture of this demodulation is thereby analog and allows the transmission of
continuous data stream of the same value as the output voltage is proportional to the
input frequency. Thus it is not mandatory to use Manchester encoding and the first bit is
correctly demodulated.
The oscillator feedback resistor controls the center frequency F
ing to the output of a dummy FSK demodulator driven by a 455 kHz internal reference
frequency which is a division of the reference crystal. The discrete components con-
nected to pin 32 DISCFILT are the loop filter of the PLL stabilizing the 455 kHz signal.
Vcc supply
DISCOUT
(MOFFSET)
Fin
For voltage measurement, the LSB weighs 85 mV and the reference voltage is 1.25V.
RBW
CTRL1[1]
M
U
X
Voltage
D
RSSI
. The XOR function translates the difference into a pulse duty
F D
M
U
X
oscillator
D
CTRL1[24]
and it actually oscillates at the Fin frequency.
ADC
A
M
U
X
D
. It is adjusted accord-
B
STATUS register
MRSSI
MVCC
1942C–WIRE–06/02
C