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ad_dds_sine_cordic: Fix sine pic to pic amplitude. 

When the tool calculates the X value for different phase widths, we
get rounding errors for every width in the interval [8;24].
Depending on the width thess errors cause overflows or smaller amplitudes
of the sine waves.
The error is not linear nor proportional with the phase. To fix the issue
a simple aproximation was chosen.
main
AndreiGrozav 2018-04-03 12:05:37 +03:00 committed by AndreiGrozav
parent 6a1853654a
commit 3dc7be3eab
1 changed files with 5 additions and 2 deletions
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7
library/common/ad_dds_sine_cordic.v
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@ -82,10 +82,13 @@ module ad_dds_sine_cordic #(
localparam ANGLE_ROT_VAL_22 = 0.0000136603783400; localparam ANGLE_ROT_VAL_22 = 0.0000136603783400;
localparam ANGLE_ROT_VAL_23 = 0.0000068301891700; localparam ANGLE_ROT_VAL_23 = 0.0000068301891700;
// 1.64676025812 = system gain // 1.64676025812 =~ system gain
localparam X_FSCALE = 1 << (CORDIC_DW); localparam X_FSCALE = 1 << (CORDIC_DW);
localparam [CORDIC_DW-1:0] X_VALUE = ((X_FSCALE/2)/1.64676025812)-3; // ((2^N)/2)/1.647... localparam APROX_DW_GAIN_ERR = (CORDIC_DW < 21) ? 4 :
(CORDIC_DW <= 24) ? 7 : 0;
// ((2^N)/2)/1.647...
localparam [CORDIC_DW-1:0] X_VALUE = ((X_FSCALE/2)/(1.64676))-APROX_DW_GAIN_ERR;
// Registers Declarations // Registers Declarations