Hybrid Agc Mode; Fast Attack Agc Mode - Analog Devices AD9361 Reference Manual

UG-570

HYBRID AGC MODE

The hybrid AGC mode is the same as the slow AGC mode with
the exception that the gain update counter is not used. Instead,
gain updates occur when the BBP pulls the CTRL_IN2 signal
high. The hybrid term arises because the BBP has taken some
control of the algorithm away from the
no longer completely automatic. Hybrid mode is enabled with the
ad9361_set_rx_gain_control_mode function.

FAST ATTACK AGC MODE

Fast attack AGC mode is intended for waveforms that burst on
and off, such as those found in TDD applications or GSM/EDGE
FDD applications. The AGC responds very quickly to overloads at
the start of a burst so that the AGC can settle to an optimum gain
FINAL OVERRANGE
COUNT EXCEEDED
VARIOUS OVERLOAD
CONDITIONS OR ENERGY LOST
AD9361 so gain control is
RXON
DECREASE
PEAK OVERLOAD
GAIN
PEAK
OVERLOAD
MEASURE POWER LOCK
LEVEL GAIN CHANGE
PEAK
OVERLOAD
STATE 4
UNLOCK GAIN MEASURE POWER PEAK
DECREASE GAIN
OVERLOAD DETECT
GAIN LOCK MEASURE
Figure 25. Fast Attack AGC High Level Stage Diagram
Rev. A
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AD9361 Reference Manual
index by the time the data portion of the signal arrives. The AGC
also has an optional slow decay that allows the gain to increase if
the signal power decreases while the AGC is locking to an
optimum gain. Fast attack mode is configured with the
ad9361_set_rx_gain_control_mode function.
When the AD9361 enters the Rx state, the fast attack AGC state
machine leaves State 0 and enters State 1 as shown in Figure 25.
Its goal is to adjust the gain index such that an optimum receive
gain is realized in a very short period of time. The AGC
progresses through several states on its way to Gain Lock, in
which state the gain does not change (unlock) unless large signal
level changes occur or if the burst ends. When the gain unlocks,
the AGC state machine moves back to its reset state and starts
over. Figure 25 shows a high-level diagram of the AGC states.
STATE 0
(RESET)
STATE 1
DETECT
PEAK
OVERLOAD
STATE 2
LOW
POWER
STATE 3 STATE 2A
LOWER POWER
LOW
DETECT
POWER
STATE 5
POWER
INCREASE
GAIN
LOW
POWER