Analog Devices ADRV9005 Reference Manual page 187

Reference Manual ADRV9001
RECEIVER GAIN CONTROL
configured to be close to the same value of dBFS, but assuming some small difference between the thresholds, then as soon as apdLowThresh
is exceeded, recovery no longer occurs. The reverse is not true. hbUnderRangeHighThresh does not prevent the gain recovery towards the
apdLowThresh. Given the strong recommendation that the apdLowThresh and hbUnderRangeHighThresh be set equally, then a condition
whereby apdLowThresh is 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 167 provides a flow diagram of the decisions of the AGC when recovering the gain in the peak detect
mode.
Figure 167. Flow Diagram for AGC Recovery in Peak Detect AGC Mode
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 overrange condition, both the
peak and the power detector can instantiate a gain decrement. In the event of an underrange, only the power detector can increment the gain.
The power detector changes gain solely at the expiry of the gain update counter. As mentioned earlier, the peak detector is 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 164 and Figure 165). Therefore, in
the peak/power detect mode, if the gain attack is instantiated by peak detectors, it is possible to perform the fast attack.
The power detector provides the RMS power measurement of the receiver data at the output of the HB filtering block. In the power detect
mode, the AGC compares the measured signal level to programmable thresholds, which provide a second order control loop, whereby the gain
is changed by the larger amounts when the signal level is farther from the target level while making smaller gain changes when the signal is
closer to the target level. This allows the gain to change faster when the level is farther from the targeted range.
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