Analog Devices ADRV9001 User Manual page 167

Reference Manual
RECEIVER GAIN CONTROL
Note that the LNA must be powered down for initial calibrations. Once it is configured or bypassed during the radio on operation, it cannot be
dynamically configured or bypassed.
To accurately apply the attenuation for different components in the datapath, the user needs to measure the external path delay associated with
the LNA and set the delay through the API command adi_adrv9001_Rx_ExternalLna_DigitalGainDelay_Set().
Properly load Rx gain table, set gain control and LNA configurations. Only LNA gain step 0 (0dB) and 1 (NdB) are needed for this
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measurement. Set the delay value as 0.
Based on gain control and LNA configurations, the following info is known:
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1. LNA gain step of N dB = LNAStepdB
2. Min gain index allowed (when LNA gain is 0dB) = minGainIndex
3. The adjacent gain index has a gain step size 0.5dB
With above info, compute the following:
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1. Gain index start and end that correspond to an N dB ADRV9001 RF attenuator only gain change is:
a. attenStartIndex = minGainIndex
b. attenEndIndex = minGainIndex + 2*LNAStepdB
2. Gain index start and end that correspond to an N dB LNA only gain change is:
a. lnaStartIndex = minGainIndex - 2*LNAStepdB
b. lnaEndIndex = minGainIndex
Inject Rx input signal at desired level, through LNA into RX input port
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Initialize ADRV9001 with all initial calibrations properly performed including Rx Gain Delay Initial Calibrations.
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Perform measurement 1 – capture Rx data with attenuator only gain change
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Perform measurement 2 – capture Rx data with LNA only gain change
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Analyze both captures to determine the timing when gain change starts (t1 for RF attenuator gain change and t2 for LNA gain change). The
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LNA delay is calculated as (t2-t1)*ADRV9001 AGC clock/4.
It is recommended to use the external LNA gain control based on the default Rx gain table, as shown in the above example. However, the
ADRV9001 allows to define the minimum gain index in the default Rx gain table (for example, set the minimum gain index to be 211 instead
of 195) to accommodate the gain control requirements in the applications. The minimum gain index (minGainIndex) can be set in the LNA
configuration structure "adi_adrv9001_RxLnaConfig_t".
As mentioned, two AGPIO pins are used for each receiver to perform external gain control. Depending on the hardware register setting,
the AGPIO pins for Receiver 1 and Receiver 2 are selected from AGPIO[3:0], AGPIO[7:4], and AGPIO[11:8].
of Receiver 1 and Receiver 2 external gain element control when AGPIO[0:3] is selected (note that it is also possible to use AGPIO[1:0]
for Receiver 2 and AGPIO[3:2] for Receiver 1). For more details, see the
section.).
Table 69. An Example of Analog GPIOs for External Gain Element Control
Receiver
Rx1
Rx2
Enable these AGPIOs as outputs and set for external gain functionality. The programmed 2-bit value is directly related to the status of these
AGPIO pins. For example, if the external gain word of the Receiver 1 gain table is programmed to three in the selected gain index, then the
AGPIO[0] and AGPIO[1] are high if AGPIO[1:0] is used to control the external gain element, as the example shown in
analog.com
General-Purpose Input/Output (GPIO) and Interrupt Configuration
AGPIO Pins to Control External Gain Element
AGPIO[1:0]
AGPIO[3:2]
ADRV9001
Table 69 shows an example
Figure 151
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