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AR# 39223

Logicore DUC/DDC Compiler v1.1 - What is the difference between the raster frequency step size in the GUI and the air standard raster requirement in the datasheet?


For the Logicore DUC/DDC Compiler v1.1, what is the difference between the raster frequency step size in the GUI and the air standard raster requirement in data sheet DS766?

For example, inthe data sheet, the minimum frequency raster for LTE is 200 kHz, but on the GUI for the IP the frequwncy raster is 20 kHz. Which is correct?


There is a difference in the concepts of air standard raster requirement versus DDS frequency raster capability.

A rasterized DDS is capable of generating only those frequencies which fall on a raster defined by a particular "raster" or step size.

The air standard raster specification states the minimum requirement for carrier separation and, therefore, the minimum requirement for DDS programmability (i.e what is the maximum step size at which the DDS needs to be programmable). The maximum step size requirement is useful in determining the upper limit for the DDS raster requirement, but the DDS is capable of being programmed to a finer granularity. The DDS raster is determined based on a number of factors like:

a) the air standard raster requirement
b) the desired mixing frequency
c) the individual channel bandwidth.

This value may be less than or equal to the minimum carrier separation from the air standard raster specification. For example, in the data sheet this is 200 kHz.

The frequency raster reported in the GUI is the DDS raster capability (i.e. the step size at which the DDS can be programmed). For example, 20 kHz.

- we do not physically restrict the user from programming carrier frequencies which violate the minimum carrier separation (that would cost extra logic unnecessarily), we simply make sure it is possible to achieve the required minimum carrier separation exactly. The user needs to know the programming raster in order to know what numeric values to program into the carrier frequency registers:

Register value = Desired Frequency / DDS Raster

For ease of use by software, the frequency raster is also reported as a constant which can be read at register location 0x088; this allows the software to be generic and read the raster from a fixed location and determine the programming values automatically based on absolute desired frequency values.

AR# 39223
Date 12/15/2012
Status Active
Type General Article
  • ISE Design Suite - 12.1
  • ISE Design Suite - 12.2
  • ISE Design Suite - 12.3
  • DUC/DDC Compiler
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