Analog Devices ADRV9001 User Manual page 100

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device goes through a variable gain amplifier (VGA), a low pass filter (LPF) and a power amplifier before transmitting through antenna.
In the receive path, typically, the RF signal receiving from antenna goes through a low noise amplifier (LNA) and a band pass filter (BPF)
before sending to the device. The duplexer is for supporting both FDD and TDD modes, which could stand for a frequency duplexer in
FDD mode and a RF switch in TDD mode.
As shown in Figure 95, for each Rx, besides acting as a primary data channel for receiving RF signals, it could also serve as an observation
channel, which receives loopback signals from Tx. There are 3 loopback paths, which are internal loopback (ILB), external loopback type
1 (ELB1) and external loopback type 2 (ELB2) as shown in Figure 95. When users are in full control of the loopback channel for running
their own algorithms, we rename the Rx as observation Rx (ORx). In such a case, user can use either ELB1 or ELB2 depending on the
algorithm requirements. For example, if running an external DPD, user should utilize the ELB2 path.
ANTENNA A
ANTENNA B
The 3 loopback paths could also be used internally by ADRV9001 for two major purposes: Tx init calibrations and Tx tracking
calibrations including the integrated digital pre-distortion (DPD) operation. Tx init calibrations is to configure the device properly based
on system configurations during the initialization time. It can be done through either ILB, ELB1 or ELB2. The major advantage of using
ELB1 comparing with ILB is to observe common mode voltage. In addition, during Tx init calibrations procedure, test tones are
generated and present at Tx output. Therefore, user needs to ensure appropriate level of isolation from ADRV9001 Tx output to antenna
to ensure that test tones are not transmitted by the system. This isolation could be achieved by disabling power amplifier during Tx init
calibration in ELB1. For ELB2, the calibration signal might be transmitted out through the antenna. Although the power level of
calibration signal is set as low as possible, the user should make sure that this will not cause any problem when using this option. See the
Transmitter/Receiver/Observation Receiver Signal Chain Calibrations section for more information.
Tx tracking calibrations is to tweak the system on the fly during its normal operations for optimal performance. Similarly, it could utilize
ILB, ELB1 or ELB2. ILB and ELB1 are used when DPD is not required while ELB2 is used when DPD is required, in which the Tx
transmit signal is looped back to the receiver after power amplifier. Note ELB1 and ELB2 shares the same Rx input, so they can't be used
simultaneously.
No matter used by user or internally by the device, the observation channel shares the same datapath as the regular Rx, therefore the
observation can only be performed when no regular Rx reception is required at the same time. This is the case for Tx init calibrations and
the user should aware that Rx might not be idle since it works as observation channel during the time period of initialization internally
by the device. Different from Tx init calibrations, Tx tracking calibrations are performed on the fly, so they have to time share with the
regular Rx operations. For example, in a TDD system, when Tx is transmitting Rx should not be receiving, therefore, it could be used for
observation for Tx tracking calibrations. For a system where Rx is fully occupied all the time for receiving RF signals, such as a 2Tx2Rx
FDD system, it is not possible to perform Tx tracking calibrations including DPD operations in such a system. However, in a 1Tx1Rx
FDD system, since 1 Rx is always idle, it can be used as an observation channel. For example, if Tx1 is transmitting, then Rx1 can be used
for observation by receiving loop back signals from Tx1 and Rx2 can be used as the main receive path. Note it is required that the
observation must be at the same side of the Tx it observes so observation Channel 1 is always for Tx1 and observation Channel 2 is
PA LPF
ELB2
DUPLEXER
(TDD,FDD)
LNA BPF
LNA BPF
DUPLEXER
(TDD,FDD)
ELB2
LPF
PA
Figure 95. ADRV9001 Rx/ORx/Loopback Diagram
Rev. PrA | Page 100 of 253
Preliminary Technical Data
ADRV9001
VGA TX1 TX1
ILB
ILB INPUT
ELB1
Rx1B
RX1/ ORX1
Rx1A
Rx2A
RX2/ ORX2
Rx2B
ELB1
ILB INPUT
ILB
VGA
TX2 TX2