Analog Devices ADRV9001 User Manual page 165

Reference Manual
RECEIVER GAIN CONTROL
In this gain table, each row provides a unique combination of six fields, including front-end attenuator, TIA control, ADC control, external gain
control, phase offset, and digital gain/attenuator. Among them, the TIA control that sets the TIA gain, ADC control that sets the ADC gain, and
phase offset that compensates for the phase discontinuity during gain change are reserved for future use.
Based on the table row selected, either manually in the MGC mode or automatically in the AGC mode, the gain control block updates the
variable gain elements depicted by the dash lines. In the MGC mode, the user controls the variable gain elements through the same gain table
using the API commands and DGPIOs.
Table 67 shows the first three and the last three rows in a sample gain table.
Table 67. Sample Rows from the Default Rx Gain Table
Gain Table Front-End Attenuator Control
Index Word [7:0]
187 248
188 247
189 250
... ...
253 28
254 14
255 0
The gain table index is the reference for each unique combination of gain settings in the programmable gain table. The current possible range
of the gain table is 187 to 255. The gain index region is user configurable. Call an API function adi_adrv9001_Rx_MinMaxGainIndex_Set()
right after loading the gain table to load multiple gain table regions and switch between multiple gain table regions during runtime.
The front-end attenuator and digital gain/attenuator are the two fields used in the default gain table. The front-end attenuator is an 8-bit control
word. The amount of attenuation applied depends on the value set in this column of the selected gain table index. The following equation
provides an approximate relationship between the attenuation in dB and the front-end attenuation control word programmed in the gain table,
Attenuation dB = 20log
N:
It is shown that index 255 denotes a 0 dB front-end attenuation and the step size between the adjacent gain index is approximately 0.5 dB.
Note that when the index is below 195, the actual step size becomes less accurate.
The digital gain/attenuator column is used to apply the gain or attenuation digitally. The 11-bit signed word defines the digital gain applied,
which equals the control word times 0.05 in dB.
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
67 stands for a receiver gain correction table. The
used as an observation channel (ORx). Note that there is another gain table to control ORx gain. However, to control ORx gain, there is no
AGC mechanism but only MGC. In addition, the digital gain is only for gain correction.
analog.com
Figure 150. Rx Datapath and Gain Control Blocks
TIA ADC
Control Control
0 0
0 0
0 0
... ...
0 0
0 0
0 0
256 − N
10
256
Table 67 shows that for gain index 253, the digital gain is calculated as -2 × 0.05 = -0.1 dB.
Receiver/Observation Receiver Signal Chain
External Gain Control Phase Offset Digital Gain/Attenuator Control Word
[1:0]
0 0
0 0
0 0
... ...
0 0
0 0
0 0
section mentions that the receiver can also be
ADRV9001
[10:0]
-2
-17
−4
...
−2
−1
0
Table
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