Analog Devices ADRV9005 Reference Manual page 180

Reference Manual
RECEIVER GAIN CONTROL
There are two types of receiver gain tables. One is for gain correction, in which the digital gain is for correcting the small step size inaccuracy
in the front-end attenuator. The other one is for gain compensation, which compensates the entire front-end attenuation. The example
71 stands for a receiver gain correction table. The
used as an observation channel (ORx).
The receive channel can also operate as an observation channel (ORx), as discussed in
a case, a different gain table is used. It provides 0 dB to 30 dB attenuation in 5 dB step size. The gain index is from 2 to 14. Gain index 14
provides 0 dB attenuation, then the next two indexes (both 13 and 12) provide 5 dB attenuation. The last two indexes (both 3 and 2) provide
30 dB attenuation. The digital gain specified in the gain table is only used for gain correction. In addition, only manual gain control is supported.
Note that the ADRV9001 also uses the ORx gain table internally for initial and tracking calibrations (see
Receiver Signal Chain Calibrations) so it should not be modified by user.
Gain Control with External Gain Control
The ADRV9001 can also control external gain such as the gain of an LNA. Configure the LNA gain by configuring the data structure
adi_adrv9001_RxLnaConfig_t and then calling the API adi_adrv9001_Rx_ExternalLna_Configure(). Based on the user configuration, the
ADRV9001 creates a new receiver gain table internally with extended gain indices to accommodate the additional LNA attenuation.
In the case of a single external gain control component, the minimum possible gain index becomes 137, which provides a maximum total of
59 dB attenuation, including the maximum LNA attenuation of 29 dB. For cases with more than one external gain control component, this
limit is relaxed as described in the
attenuation included is only 30 dB 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 two bit control word through two AGPIO pins, which yields four different
gain step sizes for each receive channel. The four step sizes are based on the attenuation relative to the max gain of LNA, and are 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 are multiple integers of 0.5 dB steps. In addition, N + M + L should not exceed 29 dB. Note that the 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.
Create the new receiver gain table first assuming the max LNA gain (0 dB) until the ADRV9001 front-end attenuator "runs out of" attenuation.
Then new gain indices are produced by assuming the LNA gain of -N dB. To achieve the desired total attenuation by maintaining the 0.5 dB
step size, recalculate the front end gain and set it 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 LNA step 2 is configured. The same method
applies to LNA step 3, if it is configured.
As an example, if the LNA is configured with step 1 of 10 dB attenuation only, the receiver gain table uses LNA with 0 dB attenuation for gain
indices from 255 to 195 and sets the external gain control word to be 0. For gain entries below 195, it switches LNA 10 dB of attenuation as the
gain index 195 has an attenuation of 30 dB to maintain 0.5 dB 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 is 30.5 - 10 = 20.5 dB, which reuses the setting associated with the index 255 – 20.5
× 2 = 214. So the entries for new gain index 194 are copied from index 214, plus the external control indicates that the 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 in table entries 213, 212, and until
it reaches 195, which exhausts the maximum front-end attenuation.
Table 72 shows the generated new receiver gain table. It has new entries from 194 to 175 to accommodate the 10 dB LNA attenuation, and
they are copied from 214 to 195 with external gain control set to be 1.
Table 72. New Rx Gain Table Created from the Default Rx Gain Correction Table
Total Effective
Gain Table ADRV9002 Attenuation
1
Index (dB)
175 30
... ...
analog.com
Receiver/Observation Receiver Signal Chain
Multiple External Gain Control Components
Total Effective
External Attenuation Front-End Attenuator
1
(dB) Control Word [7:0]
10 248 (copied from 195)
... ...
section mentions that the receiver can also be
Receiver/Observation Receiver Signal
Transmitter/Receiver/Observation
section. Note that with the extended gain table, the front-end
TIA ADC External Gain
Control Control Control [1:0]
0 0 1
... ... ...
ADRV9001
Table
Chain. In such
Phase Digital Gain/Attenuator
Offset Control Word [10:0]
0 −2
... ...
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