Other Considerations - Analog Devices AFDF7021 Application Note

Application Note
START
RSSI VALUE AT
POINT A < BEST?
YES
SET BEST = A VALUE
SET SUBOPTIMAL COUNTER = 0
INCREMENT ITERATION COUNTER
ITERATIONS
< MAX ALLOWABLE
VALUE?
YES
END
REITERATE GRADIENT
CALCULATION
Figure 10. Gradient Descent Algorithm Terminating Conditions
NO
INCREMENT
SUBOPTIMAL
COUNTER
SUBOPTIMAL
YES
< MAX ALLOWABLE
VALUE?
NO
NO
SET IR CALIBRATION
TO BEST STORED
VALUES
END
CALIBRATION
COMPLETE

OTHER CONSIDERATIONS

IR calibration evaluation software is provided by Analog
Devices. This is included with the ADF7xxx evaluation
software.
The optimum calibration values vary with temperature.
Figure 11 shows the image rejection varying with changes
in temperature. It is recommended to recalibrate when the
temperature changes by 20°C. The on-chip temperature sensor
is suitable for detecting such temperature changes. Reading
back the temperature sensor is explained in the relevant
ADF7021, ADF7021-N, and
the ADF7021 family of parts must be switched to Tx mode
when reading back the temperature sensor. Additionally, the
ADC must be enabled by writing to R8_DB8.
60
50
40
30
V = 3.0V
DD
IF BW = 25kHz
20
WANTED SIGNAL:
RF FREQ = 430MHz
MODULATION = 2FSK
10 DATA RATE = 9.6kbps,
PRBS9
f
= 4kHz
DEV
LEVEL= –100dBm
0
–60 –40
Figure 11. Image Rejection Variation with Temperature after Initial
Rev. 0 | Page 11 of 12
ADF7021-V data sheet. Note that
CAL AT +25°C
CAL AT +85°C
INTERFERER SIGNAL:
RF FREQ = 429.8MHz
MODULATION = 2FSK
DATA RATE = 9.6kbps,
PRBS11
f
= 4kHz
DEV
–20 0 20 40
TEMPERATURE (°C)
Calibrations at −40°C, +25°C, and +85°C
AN-1258
CAL AT –40°C
80
60 100