Analog Devices ADRV9001 User Manual Download Page 157

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Preliminary Technical Data

UG-1828

Rev. PrC | Page 157 of 338

example shown in Table 56 stands for a receiver gain correction table. In the Receiver/Observation Receiver Signal Chain section of this
User Guide, it mentions that receiver can also be used as ORx for signal observation. Note another gain table exists for ORx gain control.
However, for ORx gain control, there is no AGC mechanism but only MGC. In addition, the digital gain is only for gain correction.
Besides these 2 fields, the External Gain Control sets the external gain such as the gain of an LNA. User configures the LNA gain by
configuring the data structure adi_adrv9001_RxLnaConfig_t and then calling the API adi_adrv9001_Rx_ExternalLna_Configure(). Note
user should not modify the default Rx gain table. Based on user configuration, ADRV9001 creates a new Rx gain table internally with
extended gain indices to accommodate the additional LNA attenuation. In such a case, the minimum possible gain index becomes 137,
which can provide a maximum total of 59dB attenuation including the maximum LNA attenuation of 29dB. Note with the extended gain
table, the Front-end attenuation included is only 30dB to avoid gain step size inaccuracy from gain index 194 to 187.
As indicated in the default gain table, the External Gain Control uses a 2 bit control word via 2 AGPIO pins which could yield 4 different
gain step size for each receive channel. The 4 step sizes are based on attenuation relative to the max gain of LNA and defined as the
following:
step 0 (control word 0) = 0 dB
step 1 (control word 1) = -N dB
step 2 (control word 2) = -N - M dB (optional)
step 3 (control word 3) = -N - M - L dB (optional)
Gain steps N, M and L should be multiple integers of 0.5 dB steps. In addition, N+M+L should not exceed 29dB. Note N and M are
optional. The gain table maintains a gain step of 0.5 dB between adjacent gain indices and it assumes that the LNA step sizes are accurate.
The new Rx gain table is created by first assuming the max LNA Gain (0dB) until the ADRV9001 front-end attenuator “runs out of”
attenuation. Then new gain indices are produced by assuming LNA gain of -N dB. To achieve the desired total attenuation by maintaining
the 0.5dB step size, the front end gain needs to be recalculated and set properly in the new rows. Once the front-end attenuator “runs out
of” attenuation again with LNA gain of -N dB, the new gain indices are further produced by assuming LNA gain of -N-M dB if user
configures LNA step 2. The same method applies to LNA step 3 if it is configured.

As an example, if user configures the LNA with step 1 of 10 dB attenuation only,  the Rx gain table uses LNA with 0 dB attenuation for
gain indices from 255 to 195 and set the External Gain control word to be 0. For gain entries below 195 it switches LNA to 10 dB of
attenuation. Since gain index 195 has an attenuation of 30dB, to maintain 0.5dB step size,  the next gain index 194 represents 30.5 dB of
total attenuation with a 10 dB external LNA. Therefore the front end attenuation should be 30.5-10 =20.5dB, which should reuse the
setting associated with the index 255 – 20.5*2 = 214. So the entries for new gain index 194 should be copied from index 214, plus the
external control should indicate LNA is enabled with 10 dB attenuation step by using control word 1. Each lower gain entry is simply
copied from the next lower gain from table entry 213, 212, until it reaches 195 which exhaust the maximum front end attenuation.

The generated new Rx gain table is shown in Table 57. It has new entries from 194 to 175 to accommodate the 10dB LNA attenuation and
they are copied from 214 to 195 with external gain control set to be 1.

Analog Devices ADRV9001, User Manual

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