Analog Devices ADRV9005 Reference Manual page 179

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 71 shows the first three and the last three rows in a sample gain table.
Table 71. Sample Rows from the Default Rx Gain Table
Gain Table Total Effective ADRV9001
1
Index Attenuation (dB)
187 34
188 33.5
189 33
... ...
253 1
254 0.5
255 0
1
This column is not part of the Rx Gain Table and included only for illustrative purposes.
2
TIA Control is a legacy component and won't be included in ADRV9001.
3
ADC Control is a legacy component and won't be included in ADRV9001.
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.
analog.com
Figure 162. Rx Datapath and Gain Control Blocks
TIA
Front-End Attenuator
Control
Control Word [7:0]
248 0
247 0
250 0
... ...
28 0
14 0
0 0
256 − N
10
256
Table 71 shows that for gain index 253, the digital gain is calculated as -2 × 0.05 = -0.1 dB.
ADC
External Gain
2 3
Control
Control [1:0]
0 0
0 0
0 0
... ...
0 0
0 0
0 0
ADRV9001
Digital Gain/Attenuator Con-
trol Word
Phase
[10:0]
Offset
0 −2
0 −17
0 −4
... ...
0 −2
0 −1
0 0
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