UG-570 AD9361 Reference Manual
| Page 10 of 128
BASEBAND Tx ANALOG FILTER CALIBRATION
The baseband Tx analog filter calibration tunes the cutoff
frequency of the third-order Butterworth Tx anti-imaging filter.
The Tx filter is located just after the DAC in the Tx signal path
and is normally calibrated to 1.6× the BBBW. Note that the
BBBW is half the complex bandwidth and coerced between
20 MHz to 0.625 MHz for the equations used in this filter
tuning. To generate this Tx tune clock, the BBPLL is divided
down using a divide by 1 to 511 divider dedicated to the Tx
tuner block.
=
× ()
,
× . ×
(6)
The Tx baseband analog filter calibration runs as part of the
ad9361_set_tx_rf_bandwidth. Calibration completion can be
monitored on a control out pin or by reading calibration
control until the Tx baseband filter calibration bit self clears.
,
=
× ()
. × ×
(7)
= 355 ×
()
,
× . ×
(8)
Similar to the baseband Rx analog filter, there is quantization of
the corner frequency for the Tx analog filter as well. If the
quantization becomes too large it may be necessary to adjust the
desired BBBW.
Table 6. Typical Tx Baseband Filter Calibration Times
Standard
Desired
BBBW (MHz)
BBPLL Frequency
(MHz)
TxBBF Divider
(decimal)
Actual BBBW (MHz)
Max Calibration
time (µs)
LTE 5 MHz 2.5 983.04 28 35.1086 10.1115
LTE 10MHz 5 983.04 14 70.2171 5.0558
LTE 15 MHz 7.5 737.28 7 105.326 3.3705
LTE 20 MHz 10 983.04 7 140.434 2.5278
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