Analog Devices ADRV9005 Reference Manual page 192

Reference Manual
RECEIVER GAIN CONTROL
Half-Band Peak Detector
The HB peak detector is located in the digital domain at the output of the HB filtering block. It can, therefore, also be referred to as the
decimated data overload detector because it works on decimated data. Like the APD detector, it functions by comparing the signal level to
programmable thresholds. It monitors the signal level by observing individual samples (I2 + Q2 or peak I/peak Q) over a period of time and
compares these samples to the threshold. If a sufficient number of samples exceed the threshold in the period of time, then the threshold is
noted as exceeded by the detector. hbOverloadDurationCount controls the duration of the HB measurement, while hbOverloadThreshCount
controls the number of samples that should exceed the threshold in that period.
Once the required number of samples exceeds the threshold for the duration required, the detector records that the threshold is exceeded. Like
the APD detector, the HB detector requires a programmable number of times for the threshold to be exceeded in a gain update period before it
flags an overrange condition.
Figure 171 shows the two-level approach, which is different from APD. It shows the gain update counter period, with the time broken
into subsets of time based on the setting of hbOverloadDurationCount. Each period is considered separately, and hbOverloadThreshCount
individual samples must exceed the threshold within hbOverloadDurationCount to declare an overload. These individual samples greater
than the threshold are shown in gray. Two examples are shown; one where the number of samples exceeding the threshold is sufficient
for the HB peak detector to declare an overload, and a second example where the number of samples exceeding the threshold is not
sufficient to declare an overload. The number of overloads is counted, and if the number of overloads of the hbHighThresh exceeds the
hbUpperThreshPeakExceededCount in a gain update counter period, an overrange condition is called. Likewise, if the number of overloads
of the hbUnderRangeHighThresh does not exceed hbUnderRangeHighThreshExceededCount, an underrange condition is called. Note that
if hbOverloadDurationCount is set to equal to the time duration of one sample and hbOverloadThreshCount is set to one, the HB two-level
approach becomes similar to the APD algorithm.
The HB detector has a number of programmable thresholds. Some of these thresholds are only used in the fast recovery mode of the peak
detect AGC configuration, as summarized in
Table 84. HB Overload Thresholds
HB Threshold
hbHighThresh
hbUnderRangeHighThresh
hbUnderRangeMidThresh
hbUnderRangeLowThresh
For more details of how the AGC uses these thresholds, see the relevant sections in this document. The thresholds are related to an ADC
dBFS value using the following equations.
ℎbHigℎTℎresℎ = 16384 × 10
ℎbUnderRangeHigℎTℎresℎ = 16384 × 10
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Figure 171. HB Detector, Two-Level Approach for an Overload Condition
Table 84.
Use
Gain attack in both peak and peak/power detect AGC modes.
Gain recovery in peak detect AGC mode. In the peak/power detect AGC mode, it prevents overloads during gain
recovery.
Only when the fast recovery option of the peak detect AGC mode is being used.
Only when the fast recovery option of the peak detect AGC mode is being used.
ℎbHigℎdBFS
20
ℎbUnderRangeHigℎdBFS
20
ADRV9001
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