Analog Devices ADRV9001 User Manual page 171

Reference Manual
RECEIVER GAIN CONTROL
It is highly recommended that the apdHighThresh and hbHighThresh are set to an equivalent dBFS value. Likewise, it is highly recommended
that the apdLowThresh and the hbUnderRangeHighThresh are set to equivalent values. This equivalence is approximate, as these thresholds
have unique threshold settings and are not exactly equal. This section discusses the relevant priorities between the detectors and how the AGC
reacts when multiple threshold detectors are exceeded.
Table 75. Priorities of Attack Gain Steps
apdHighThresh Overrange
No
No
Yes
Yes
Note that in the case of apdHighThresh Overrange is Yes, but hbHighThresh Overrange is No, there are two possibilities: one is due to the
out-of-band blocker, which is only observed by the APD, the other one is due to a low frequency signal near DC. In the second case, when the
signal is near DC, due to the characteristics of the APD, it might generate positive overrange conditions. To overcome this issue, a mitigation
mode is designed, which utilizes a secondary digital threshold to decide if the APD overrange is a false positive. When the mitigation mode is
turned on, if the secondary threshold is exceeded, then it confirms a false positive due to a signal near DC, so the gain does not change. If the
secondary threshold is not exceeded, then it confirms an out-of-band blocker, so the gain is decremented. In the current implementation, the
mitigation mode is always turned on, and the user is not allowed to configure the secondary digital threshold.
For recovery, the number of thresholds is dependent on whether fast recovery is enabled or not. Considering this, the fast recovery scenario
and the priority of the thresholds is:
1. hbUnderRangeLowThresh Underrange Condition
2. hbUnderRangeMidThresh Underrange Condition
3. hbUnderRangeHighThresh Underrange Condition
4. apdLowThresh Underrange Condition
Upon one underrange condition, the AGC changes the gain by the corresponding gain step size of this condition. However, if multiple
conditions occur simultaneously, then the AGC prioritizes based on the priorities indicated; i.e., if hbUnderRangeLowThresh is reporting an
underrange condition, then the AGC adjusts the gain by hbGainStepLowRecovery with two exceptions.
The apdLowThresh has priority in terms of preventing recovery. If apdLowThresh reports an overrange condition (sufficient signal peaks have
exceeded its threshold in a gain update counter period), then no further recovery is allowed. apdLowThresh and hbUnderRangeHighThresh are
analog.com
Figure 154. AGC Operation with HB Detector in Fast Recovery Mode
Table 75 shows the priorities between the detectors when multiple overranges occur.
hbHighThresh Overrange
No
Yes
No
Yes
ADRV9001
Gain Change
No Gain Change
Gain Change by hbGainStepAttack Gain
Change by apdGainStepAttack
Gain Change by apdGainStepAttack
Rev. 0 | 171 of 351