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AD9174

Data Sheet

Rev. A | Page 58 of 164

PDP

JESD204B

ERRORS

SPI

BSM

IRQ0/IRQ1

TXEN0/TXEN1

(LONG/SHORT) PDP_PROTECT

SPI_PROTECT

SPI_TXEN

TXEN

INTERFACE_PROTECT

FLUSH

DATAPATH

DAC

CORE

CHANNEL

SUMMER

CHANNEL

DATAPATHS

BYPASSED

NCO

RAMP UP/DOWN

GAIN

BSM_PROTECT

ERROR

TRIGGER

SOURCE

ENA_SPI_TXEN

Figure 76. Block Diagram of Downstream Protection Triggers

I2 + Q2

SHORT AVERAGE

FILTER

(2.6ns, 1.0µs) AT 12GHz

LONG AVERAGE

FILTER

(1.0µs, 1.0ms) AT 12GHz

SHORT_PA_THRESHOLD

DATAPATH

DATA SAMPLES

LONG_PA_THRESHOLD

LONG_PDP_PROTECT/

SHORT_PDP_PROTECT

Figure 77. PDP Block Diagram

Power Detection and Protection (PDP) Block

The PDP block calculates the anticipated average power at the

DACx core output and prevents overrange signals from being

output from the AD9174, to avoid a potentially destructive

breakdown of power sensitive devices, such as PAs. The protection

block provides a signal, PDP_PROTECT, that can be used ramp

down the DAC output and/or be routed to an I/O pin to flag

external components to shut down.

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 (with the

exception when the total interpolation is 1×). The sum of I2 and

Q2 are calculated as a representation of the input signal power

(to improve response time, only the top six MSBs of data

samples are used). The calculated sample power values are

accumulated through a moving average filter with an output

that is the average of the input signal power across a certain

number of samples. There are two types of average filters with

different lengths: a short filter that detects high power pulses

that may result in voltage breakdown, and a long filter that

detects sustained high power signals that may last longer than

the thermal constant of the PA or another device.

When the output of the averaging filter is larger than the

threshold, the internal signal, PDP_PROTECT, goes high,

which can optionally be configured to trigger an IRQ flag and

turn off the DAC output through the ramp-up/ramp-down.

The PDP block function is illustrated in Figure 77.

The long and short averaging times are 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

following 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

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