Baseband Tx Analog Filter Calibration - Analog Devices AD9361 Reference Manual

UG-570

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
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tuner block.
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Table 6. Typical Tx Baseband Filter Calibration Times
Desired
Standard
BBBW (MHz)
LTE 5 MHz 2.5
LTE 10MHz 5
LTE 15 MHz 7.5
LTE 20 MHz 10
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× 3.2 × ��
BBPLL Frequency
(MHz)
983.04
983.04
737.28
983.04
Rev. A
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
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control until the Tx baseband filter calibration bit self clears.
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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.
(6)
TxBBF Divider
Actual BBBW (MHz)
(decimal)
28 35.1086
14 70.2171
7 105.326
7 140.434
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AD9361 Reference Manual
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Max Calibration
time (µs)
10.1115
5.0558
3.3705
2.5278
(7)
× 3.2 × π
(8)