Analog Devices ADRV9001 User Manual page 162

UG-1828
The apdLowThresh has priority in terms of preventing recovery. If apdLowThresh reports an over range condition (sufficient signal peaks
have exceeded its threshold in a gain update counter period), then no further recovery is allowed. apdLowThresh and
hbUnderRangeHighThresh should be configured to be as close to the same value of dBFS, but assuming some small difference between
the thresholds, then as soon as apdLowThresh is exceeded, recovery will no longer occur. The reverse is not true,
hbUnderRangeHighThresh will not prevent the gain recovery towards the apdLowThresh. Given the strong recommendation that
apdLowThresh and hbUnderRangeHighThresh being set equally, then a condition whereby apdLowThresh was at a lower dBFS level to
hbUnderRangeLowThresh or hbUnderRangeMidThresh should not occur.
Another exception is if the recovery step size for a detector is set to zero. If so, the AGC makes the gain change of the highest priority
detector with a non-zero recovery step. Figure 153 provides a flow diagram of the decisions of the AGC when recovering the gain in peak
detect mode.
N
apdLowThresh under-range
AND apdGainStepRecovery
Peak/Power Detect Mode
In this mode, the peak and power detect work jointly to control the gain of the receiver chain. In the event of an over-range condition,
then both the peak and the power detect can instantiate a gain decrement. In the event of an under-range, only the power detect can
increment the gain. The power detector will change gain solely at the expiry of the gain update counter. As previously mentioned, the
peak detect can be set in one of two modes (depending on the setting of gainChangeIfThreshHigh) whereby the AGC: 1) waits for the
gain update counter to expire before initiating a gain change; or 2) immediately updates the gain as soon as the overrange condition
occurs (see Figure 150 and Figure 151). Therefore, in the peak/power detect mode, if the gain attack is instantiated by peak detectors, it is
possible to perform fast attack.
N
IF
N
hbUnderRangeHighThresh
under-range AND
hbGainStepHighRecovery
NOT 0
IF
Y
NOT 0
RECOVER GAIN BY
apdGainStepRecovery
Figure 153. Flow Diagram for AGC Recovery in Peak Detect AGC Mode
GAIN RECOVERY
IF
Y
apdLowThresh
under-range
N
hbUnderRangeLowThresh
hbGainStepLowRecovery
IF
N
hbUnderRangeMidThresh
under-range AND
hbGainStepMidRecovery
NOT 0
Y
RECOVERY GAIN BY
hbGainStepHighRecovery
END
Rev. PrC | Page 162 of 338
Preliminary Technical Data
IF
Y
under-range AND
NOT 0
Y
RECOVERY GAIN BY
hbGainStepLowRecovery
RECOVERY GAIN BY
hbGainStepMidRecovery