512-point Sine

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FreeCore Function #9:
512-point Sine
Module name: sine
Current release: version 1.0, August 19, 1997
Contributed by: Rune Baeverrud

Introduction

Shown below is the schematic representation of the Sine Module.

The Sine Module has the following key properties:

512 points around the unit circle (128 points / quadrant), using single 256 point lookup-table (one EAB).
7 bits + sign bipolar or 8 bit unipolar output resolution, giving Signal-to-Noise Ratio (SNR) = 50,23dB.
Cosine table generated with the MIFGEN utility, see below for details.
Variable length pipeline for up to 80MHz operation.

Based on the Cosine Module

The Sine Module is based on the Cosine Module. The parameters are all passed through - the Sine Module only modifies the Angle input to provide a 90 degrees phase shift into the Cosine Module.

The Cosine Look-up Table

The cosine look-up table was generated using the MIFGEN utility also available on this web site. The MIFGEN utility was set up with the following parameters:

Angle range = "0-180 degrees"
Peak Amplitude = 126.20
Number of Samples = 256
Number of Bits = 8
Function = "Cosine"
Options = "Symmetry"

Two files exists, one with Offset = 0 named "COS180N.MIF" and another with Offset = 128 named "COS180P.MIF". COS180N.MIF will be used if parameter POLARITY is set to "BIPOLAR", and COS180P.MIF will be used if parameter POLARITY is set to "UNIPOLAR". Options = "Symmetry" was chosen, requiring absolutely no manipulation of the look-up table output. This gives the advantage of high speed and very compact design. The amplitude was chosen to 126.2 - giving the highest possible SNR and therefore the closest approximation to a pure cosine.

High Speed

With no pipelining (all levels set to "UNREGISTERED") a speed of 30-40 MHz is achievable in a FLEX 10K -3 device. With level 1, 2 and 3 set to "REGISTERED" (3 levels of pipeline) a speed of above 80MHz is achievable in a FLEX 10K -3 device.

Module Parameters

PARAMETERS
POLARITY	Set to "UNIPOLAR" (1..128..255) operation or "BIPOLAR" (-126..0..126) operation (using 2's complement).
LEVEL1	Should be "REGISTERED" or "UNREGISTERED". Level 1 is the output of the subtractor ("angle/index modifier") and multiplexer which feeds the EAB look-up table.
LEVEL2	Should be "REGISTERED" or "UNREGISTERED". Level 2 is the input registers in the EAB look-up table.
LEVEL3	Should be "REGISTERED" or "UNREGISTERED". Level 3 is the output registers in the EAB look-up table.
INPUT PORTS
SysClk	System clock input.
Angle[8..0]	9 bits (512 indexes) input giving the relative angle on the unit circle. Values 0-255 correspond to angles in the 0-180 degree range, values 256-511 correspond to angles in the 180-360 degree range.
OUTPUT PORTS
Wave[7..0]	Digital Waveform output, unipolar or bipolar, depending on the POLARITY parameter setting.

NOTE: You need to copy the files COS180N.MIF and COS180P.MIF to your current working directory.

Enjoy!