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Voyager
Voyager
2,099 Views
Registered: ‎06-26-2015

dds compiler phase question

when in Rasterized, both PINC and POFF is adjust base on the raster modulus parameter?  for example if I want phase offset of 90degree from my current output wave, do I just  (M-1)/4 round of to integer?  something like that?  also the output phase port, is that the current phase for the data?

 

same for PINC, I adjust the M parameter for my phase increment   where delta phi=fout * M/fclk ?

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Xilinx Employee
Xilinx Employee
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Registered: ‎08-01-2008

When rasterized mode is selected, the hardware values of PINC and POFF that are input or configured must be 0 to Modulus-1. This corresponds to a full circle. So for negative PINC or POFF values, add the Modulus to the negative value desired to map to the required range. For example with Modulus = 100, the required range is 0 to 99. An angle of -90° would be -25 with this Modulus. Adding 100 gives 75 (270°)

 

The rasterized mode of operation of the DDS does not truncate the accumulated phase. Rasterized operation is intended for configurations where the desired frequency is a rational fraction of the system clock (output frequency = system frequency * N/M, where 0 < N < M). Values of M from 9 to 16384 are supported. The SIN/COS LUT is configured accordingly for values from 0 to M-1, which describe a full circle. Because there is no phase truncation in the rasterized mode of operation, there is no need for dither or Taylor correction because these mitigate the effects of phase truncation. In rasterized operation, the phase noise is significantly reduced. Therefore, the output phase angle resolution and amplitude resolution are determined by the LUT table output width alone. In rasterized mode, quadrant symmetry is exploited where applicable to reduce memory use.

 

For rasterized mode, phase increment values must be considered unsigned due to the internal implementation. The phase increment values [0 to Modulus-1] describe the range [0,360].

 

The phase values in rasterized mode are positive integers in the range 0 to Modulus-1. Therefore the PHASE_OUT field is padded with zeros up to the next multiple of 8 bits and becomes m_axis_phase_tdata

 

When the DDS is configured for rasterized mode, both PINC and POFF values (fixed, programmable or streaming) are expected to be in the range 0 to Modulus-1. Values outside this range are not supported and can lead to erroneous output. The signals event_pinc_invalid and event_poff_invalid are asserted when a value outside the supported range is detected

 

For rasterized mode, the frequency resolution is fixed by the system clock

Thanks and Regards
Balkrishan
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Voyager
Voyager
2,046 Views
Registered: ‎06-26-2015

 raster is more accurate due to fact it doesn't truncate the bit and lower phase noise etc?  is there any advantage of standard mode over raster?  my design require constant config of phase inc/offset, which I belief streaming config is the best.  for this purpose is there any reason standard mode is better than raster?

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Voyager
Voyager
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Registered: ‎06-26-2015

as for phase_out padding, this is extend the MSB to 16 bits right?
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