Analog Devices ADRV9001 User Manual page 175

Preliminary Technical Data
To find the best model tap order for a specific power amplifier design model, the user can take the following recommended procedures:
1. Set the amplifier output power to have a compression ratio of 1 dB or slightly less, as shown in Figure 1, i.e. the maximum peak of
the output signal is 1 dB below ideal linearity.
2. Determine the initial highest polynomial order of the main tap, TAP1, by measuring the spectral regrowth bandwidth to carrier
bandwidth ratio. All lower order polynomial terms must be included. For example, if the bandwidth ratio is 5, set the initial highest
polynomial to k = 5,that is, x(t – 1)|x(t – 1)|
3. Set the other taps to zeros, that is, turn off the other taps.
4. Use only TAP1 to execute DPD with order 5, then 6, and 7 (i.e. up to two orders above the initial estimate). Measure the ACPR for
each case. Select the one that yields a better ACPR. If the difference is small, select a lower order one, say 5.
5. While keeping the main tap determined above, set the side taps, TAP0 and TAP2, to about half the order of the main tap. In the
above example, the main tap has an order of 5, select the initial side tap order to be 2. Execute DPD with the main tap of order 5,
and the side tap order of 2, then 3, and 4. Select the side tap order that yields the lowest ACPR, say 3.
6. While keeping the main tap and side tap orders determined above, set the initial cross term tap order, TAP3, to be 2. Execute DPD
with the cross-term tap order of 2 and 3. Select none, 2 and 3, which yields the best ACPR. If the difference is small, select the lower
order one, including "none" taps. Some power amplifiers do not need a cross term.
7. Iterate the above procedure as necessary with different combinations until you are confident with the selections. Keep all tap order
selections to be minimal that satisfies your ACPR requirement with a 5 dB margin, which helps to keep DPD more stable. For
example, if your ACPR requirement is −60 dB, set your ACPR target to be −65 dB.
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