Analog Devices ADRV9005 Reference Manual page 191

Reference Manual
RECEIVER GAIN CONTROL
There are two APD thresholds, as shown in
apdLowThresh, respectively. The thresholds are typically considered relative to the full scale voltage of the ADC, which is 850 mV peak. The
mV setting of the APD thresholds is determined using the following equations.
To determine the setting of the APD thresholds in terms of the closest possible setting in terms of dBFS of the ADC assuming apdHighdBFS
and apdLowdBFS for apdHighThresh and apdLowThresh, respectively, the following equations can be used.
The APD threshold must be exceeded a programmable number of times within a gain update counter period before an overrange condition
occurs. Both the upper and lower thresholds have a programmable counter in the API structure, as indicated in
Table 82. APD Programmable Threshold Counters
Threshold
Upper Threshold (apdHighThresh)
Lower Threshold (apdLowThresh)
The Automatic Gain Control (AGC)
peak/power detect mode, the APD can be used for gain attack and is used to prevent overloading during gain recovery. For more details, see
the Automatic Gain Control (AGC)
In the AGC mode, the APD has programmable gain attack and gain recovery step sizes, as shown in
Table 83. APD Attack and Recovery Step Sizes
Gain Change
Gain Attack
Gain Recovery
Step size refers to the number of indices in the gain table when the gain is changed. As mentioned earlier, the gain table is programmed
with the largest gain in the Max Gain Index (typically index 255), with ever decreasing gain for decreasing gain index. Thus, if APD gain
attack step size is programmed to six, then this means that the gain index is reduced by six when the apdHighThresh is exceeded more than
apdUpperThreshPeakExceededCnt times. For example, if the gain index is 255 before this overrange condition, then the gain index reduces
to 249. The amount of gain reduction this equates to is dependent on the gain table in use. The default table has 0.5 dB steps, which in this
example equates to a 3 dB gain reduction upon an APD overrange condition.
The APD is held in reset for a configurable amount of time following a gain change to ensure the receiver path is settled at the new gain setting.
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Figure 170. Analog Peak Detector Thresholds
Figure 170. These thresholds are contained in the agcPeak API structure, apdHighThresh, and
section shows that the APD is used for both gain attack and gain recovery in the peak detect mode. In the
section.
Step Size
apdGainStepAttack
apdGainStepRecovery
Counter
apdUpperThreshPeakExceededCnt
apdLowerThreshPeakExceededCnt
Table
ADRV9001
Table 82.
83.
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