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b. FIFOs should have a means to detect and recover automatically from upsets that might cause overflow/

underflow conditions.

5. the user may program JTT to get an additional level of protection from functional interrupts.

9.1.7.3 NCO Reliability

The NCO does not include radiation immune flip-flops; however, there are two general strategies described in

the following sections that can be employed to make sure the NCO recovers from upset events.

9.1.7.3.1 NCO Frequency and Phase Correction (Strategy #1)

This strategy uses a periodic reference signal to correct any upsets in the NCO accumulator. This strategy is

appropriate for phased-array systems or other systems where the NCO phase must remain coherent with other

system components.

1. Program NCO_AR=1 to configure the accumulator to be reset on every synchronization event.

2. Configure the NCO to use SYSREF as the synchronization source (NCO_SYNC_SRC=2). Program

SPI_SYNC=1.

3. Make sure the SYSREF generator is configured for continuous/periodic output.

4. Since the accumulator is reset periodically, the user must make sure that the programmed NCO frequency is

an integer multiple of the SYSREF frequency. Consider the frequency raster that the system requires when

choosing the SYSREF frequency.

5. If the user cannot choose a SYSREF frequency that satisfies the frequency raster and is also a sub-

harmonic of the multiframe/EMB frequency, then use the LSB of the JESD204C data stream to periodically

synchronize the NCO. Use NCO_SYNC_SRC=3, and provide a periodic reference signal on the LSB of the I

samples for DUC0.

6. If any NCO accumulator or internal frequency register is upset, it is restored on the next synchronization

event.

9.1.7.3.2 NCO Frequency Correction (Strategy No. 2)

This strategy also uses a periodic synchronization signal, but the NCO accumulator is not reset. Only the internal

frequency registers inside each NCO are corrected by the synchronization signal. This makes sure the NCO

returns to the proper frequency after an upset occurs, but the phase of the NCO is not corrected. This strategy is

appropriate for non-phased-array systems where an occasional, arbitrary phase jump can be tolerated.

1. Program NCO_AR=0 to configure the accumulator to NOT be reset by a synchronization event.

2. Configure the NCO to use SYSREF as the synchronization source (NCO_SYNC_SRC=2). Program

SPI_SYNC=1.

3. Make sure the SYSREF generator is configured for continuous/periodic output.

4. Since the accumulator is not reset periodically, the user has the freedom to program any NCO frequency

regardless of the SYSREF frequency. The period of SYSREF must still be a multiple of the multiframe/EMB

period.

5. While the NCO is operating, any upset to the internal frequency register is corrected on the next SYSREF

pulse (the frequency word is re-copied from the SEU-immune FREQ register). The NCO operates for a brief

time at an improper frequency before returning to the correct frequency, but with arbitrary phase.

9.2 Typical Application

9.2.1 S-Band Radar Transmitter

9.2.2 Design Requirements

S-band covers a frequency range of 2GHz to 4GHz. For this example, use a radar with signal bandwidth of

200MHz and a center frequency of 3.2GHz.

Doppler radars use the frequency shift in the returned signal to measure the velocity of object. Large reflected

signals from for example ground clutter mix with the TX and RX phase noise, which can potentially swamp the

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DAC39RF10-SP, DAC39RF10-SEP

DAC39RFS10-SP, DAC39RFS10-SEP

SBAS932A – MARCH 2024 – REVISED FEBRUARY 2026

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