Specifications

Page 28
WT1231H
RssiValue
[dBm]
Note - RssiValue can only be read when it exceeds RssiThreshold
- The receiver is capable of automatic gain calibration, in order to improve the precision of its RSSI measurements.
This functio
n injects a known RF signal at the LNA input, and calibrates the receiver gain accordingly. This
calibration is automatically performed during the PLL start-up, making it a transparent process to the end-user
- RSSI accuracy depends on all components located between the antenna port and pin RFIO, and is therefore
limited to
a few dB. Board-level calibration is advised to further improve accuracy
0.0
RSSI Chart - With AGC
-20.0
-40.0
-60.0
-80.0
-100.0
-120.0
-120 -110 -100 -90 -80 -70 -60 -
50 -40 -30 -20 -10
0
Pin
[dBm]
Figure 9. RSSI Dynamic Curve
3.4.10. Cordic
The Cordic task is to extract the phase and the amplitude of the modulation vector (I+j.Q). This information, still in the
digital domain is used:

Phase output: used by the FSK demodulator and the AFC blocks.

Amplitude output: used by the RSSI block, for FSK demodulation, AGC and automatic gain calibration purposes.
Real- t ime
Magnitude
Q(t)
Real-time Phase
I(t)
Figure 10. Cordic Extraction