Gain Control; Overview - Analog Devices AD9361 Reference Manual

AD9361 Reference Manual

GAIN CONTROL

OVERVIEW

The AD9361 transceiver has several gain control modes that
enable its use in a variety of applications. Fully automatic gain
control (AGC) modes are available that address time division
duplex (TDD) as well as frequency division duplex (FDD)
scenarios. In addition, the AD9361
(MGC) options that allow the BBP to control the gain of the
receiver. The ad9361_set_rx_gain_control_mode function
configures all of the gain control modes.
The AD9361 receive signal path can be broken up into several
blocks as shown in Figure 18. The gain of almost all of the
blocks is variable as shown by the arrows through the shapes in
Figure 18.
RX
INPUT
LNA
has manual gain control
LMT PEAK
OVERLOAD
DETECTOR
LMT LPF
MIXER TRANS-Z LOW PASS
AMP (TIA) FILTER
Figure 18.
LNA
GAIN
GAIN INDEX
(POINTER)
Figure 19. AD9361
Rev. A
Each receiver has its own gain table that maps a gain control
word to each of the variable gain blocks in Figure 19. A pointer
to the table determines the control word values sent to each
block as shown in Figure 19. Whether automatic gain control
(AGC) or manual gain control (MGC) is used, the pointer
moves up and down the table, which changes the gain in one or
more of the blocks shown in Figure 18.
The ADC maximum input (0 dBFS) is 0.625 V peak. However,
to avoid compression the maximum recommend peak input
level to the ADC is 0.5 V peak, which is 1.9 dB lower than full
scale.
ADC PEAK LOW AVERAGE
OVERLOAD POWER
DETECTOR DETECTOR
DIGITAL
HALF-
ADC
BAND
FILTERS
DIGITAL
MILTIPLICAND
AD9361 Receive Signal Path
LMT GAIN
MIXER TIA LPF DIGITAL
GAIN GAIN GAIN GAIN
Gain Table Mapping
| Page 35 of 128
DIGITAL SAT
PEAK
DETECTOR
TO INPUT/
RX
OUTPUT
FIR
PORT
BYPASS
UG-570