AD9173 datasheet(55/144 Pages) AD

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Data Sheet

AD9173

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Rev. C | 55 of 144

Figure 73. Block Diagram of Downstream Protection Triggers

Figure 74. PDP Block Diagram

Power Detection and Protection (PDP) Block

The PDP block detects the average power of the DAC input signal

and prevents overrange signals from being passed to the next

stage, which may potentially cause destructive breakdown on pow-

er sensitive devices, such as PAs. The protection function provides

a signal, PDP_PROTECT, that can shut down the DAC outputs or

be routed externally to shut down a PA.

The PDP block uses a separate path with a shorter latency than

the datapath to ensure that PDP_PROTECT is triggered before the

overrange signal reaches the analog DAC cores (except when the

total interpolation is 1×). The sum of the I2 and Q2 are calculated

as a representation of the input signal power (only the top six MSBs

of data samples are used). The calculated sample power numbers

are accumulated through a moving average filter with an output that

is the average of the input signal power in a certain number of

samples.

There are two types of average filters with different lengths: the

short filter detects pulses with high power in the digital domain and

the long filter detects high power in the digital domain, which lasts

longer than the thermal constant of the PA.

When the output of the averaging filter is larger than the threshold,

the internal signal, PDP_PROTECT, goes high, which can optional-

ly be configured to trigger an IRQ flag and turn off the DAC output

through the ramp-up/ramp-down.

The PDP block is configured as shown in Figure 74.

The long and short averaging time is configured by the LONG_

PA_AVG_TIME (Register 0x585, Bits [3:0]) and the SHORT_

PA_AVG_TIME (Register 0x58A, Bits [1:0]) controls. Use the follow-

ing calculations to determine the average window size times:

Length of Long Average Window = 2LONG_PP_AVG_TIME + 9

Length of Short Average Window = 2SHORT_PA_AVG_TIME

When the average calculation value exceeds a specified threshold,

the ramp-down signal is triggered to ramp down the output. The

thresholds for the long and short average options are programmed

in the registers listed in Table 42, along with their respective

detected power calculation readbacks.

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