Analog Devices ADRV9001 User Manual

UG-1828 Preliminary Technical Data
Rev. PrC | Page 160 of 338
Figure 150. APD/HB Thresholds and Gain Changes Associated with Underrange and Overrange Conditions
It is possible to enable a fast attack mode whereby the AGC is instructed to reduce gain immediately when an over range condition
occurs, instead of waiting until the next expiry of the gain update counter using changeGainIfThreshHigh. This parameter has
independent controls for the APD and HB detectors. Values from 0 to 3 are valid as shown in Table 63.
Table 63. changeGainIfThreshHigh Settings
changeGainIfThreshHigh[1:0] Gain Change following APD Over range Gain Change following HB Overrange
00 After expiry of gainUpdateCounter After expiry of gainUpdateCounter
01 After expiry of gainUpdateCounter Immediately
10 Immediately After expiry of gainUpdateCounter
11 Immediately Immediately
Figure 151 shows how the AGC reacts when the changeGainIfThreshHigh is set for APD or HB detector. In this case when the interferer
appears, the gain is updated as soon as the number of peaks exceed the peak counter. It does not wait for the next expiry of the gain
update counter. Hence a number of gain changes can be made in quick succession providing a much faster attack than the default
operation. The assumption here is that if the ADC is overloaded then it is best to decrease the gain quickly rather than wait for a suitable
moment in the received signal in order to change the gain. This mode is referred as “fast attack” mode.
Figure 151. APD/HB Gain Changes with Fast Attack Enabled
Besides the “fast attack” mode, it is also possible to enable a “fast recovery” mode. This functionality is enabled with the
enableFastRecoveryLoop parameter.
This “fast recovery” mode only works with the HB detector. The operation is illustrated in Figure 136. In this mode, the “fast recovery” is
achieved by utilizing multiple low thresholds and step sizes as well as the update periods. When the signal level falls below
hbUnderRangeLowThresh, the lowest threshold, the gain is incremented the most by hbGainStepLowRecovery following the expiry of a
gain update period. Note that in the “fast recovery” mode the agcUnderRangeLowInterval is used instead of the gain update counter to set
the gain update period (This also applies to the APD.). After sufficient gain increases to bring the signal level above
hbUnderRangeLowThresh, the gain is incremented by hbGainStepMidRecovery after the expiry of agcUnderRangeMidInterval, which is
SIGNAL
LEVEL
apdHighThresh/
hbHighTresh
INTERFERER
PRESENT
INTERFERER
REMOVED
GAIN DECREMENT
(apdGainStepAttack/
hbGainStepAttack)
GAIN UPDATE
PERIOD
GAIN INCREMENT
(apdGainStepRecovery/
hbGainStepHighRecovery)
GAIN INCREMENT
(apdGainStepRecovery/
hbGainStepHighRecovery)
GAIN DECREMENT
(apdGainStepAttack/
hbGainStepAttack)
apdLowThresh/
hbUnderRangeHighTresh
24159-108
SIGNAL
LEVEL
apdHighThresh/
hbHighTresh
INTERFERER
PRESENT
INTERFERER
REMOVED
GAIN INCREMENT
(apdGainStepRecovery/
hbGainStepHighRecovery)
GAIN INCREMENT
(apdGainStepRecovery/
hbGainStepHighRecovery)
GAIN DECREMENT
(apdGainStepAttack/
hbGainStepAttack)
GAIN DECREMENT
(apdGainStepAttack/
hbGainStepAttack)
GAIN UPDATE
PERIOD
apdLowThresh/
hbUnderRangeHighTresh
24159-109

Analog Devices ADRV9001 Specifications

General

Brand	Analog Devices
Model	ADRV9001
Category	Transceiver
Language	English