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Change DDS to using signed integers to try to keep our DC bias averaged out.

This commit is contained in:
Stephen Olesen 2015-07-02 19:30:53 -06:00
parent 437e750e76
commit 7db28bff0e
2 changed files with 30 additions and 5 deletions
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10
DDS.cpp
View File

@ -140,9 +140,13 @@ uint8_t DDS::getDutyCycle() {
uint8_t phAng; uint8_t phAng;
#endif #endif
phAng = (accumulator >> ACCUMULATOR_BIT_SHIFT); phAng = (accumulator >> ACCUMULATOR_BIT_SHIFT);
uint8_t position = pgm_read_byte_near(ddsSineTable + phAng)>>(8-COMPARATOR_BITS); int8_t position = pgm_read_byte_near(ddsSineTable + phAng)>>(8-COMPARATOR_BITS);
// Apply scaling and return // Apply scaling and return
uint16_t scaled = position; int16_t scaled = position;
// output = ((duty * amplitude) / 256) + 128
// This keeps amplitudes centered around 50% duty
scaled *= amplitude; scaled *= amplitude;
return scaled>>8; scaled >>= 8;
scaled += 128;
return scaled;
} }

25
DDS.h
View File

@ -128,7 +128,28 @@ static const uint8_t ddsSineTable[1024] PROGMEM = {
}; };
#else #else
#define ACCUMULATOR_BIT_SHIFT (ACCUMULATOR_BITS-8) #define ACCUMULATOR_BIT_SHIFT (ACCUMULATOR_BITS-8)
static const uint8_t ddsSineTable[256] PROGMEM = { static const int8_t ddsSineTable[256] PROGMEM = {
0, 3, 6, 9, 12, 16, 19, 22, 25, 28, 31, 34, 37, 40, 43, 46, 49,
51, 54, 57, 60, 63, 65, 68, 71, 73, 76, 78, 81, 83, 85, 88, 90,
92, 94, 96, 98, 100, 102, 104, 106, 107, 109, 111, 112, 113, 115,
116, 117, 118, 120, 121, 122, 122, 123, 124, 125, 125, 126, 126,
126, 127, 127, 127, 127, 127, 127, 127, 126, 126, 126, 125, 125,
124, 123, 122, 122, 121, 120, 118, 117, 116, 115, 113, 112, 111,
109, 107, 106, 104, 102, 100, 98, 96, 94, 92, 90, 88, 85, 83, 81,
78, 76, 73, 71, 68, 65, 63, 60, 57, 54, 51, 49, 46, 43, 40, 37,
34, 31, 28, 25, 22, 19, 16, 12, 9, 6, 3, 0, -3, -6, -9, -12, -16,
-19, -22, -25, -28, -31, -34, -37, -40, -43, -46, -49, -51, -54,
-57, -60, -63, -65, -68, -71, -73, -76, -78, -81, -83, -85, -88,
-90, -92, -94, -96, -98, -100, -102, -104, -106, -107, -109, -111,
-112, -113, -115, -116, -117, -118, -120, -121, -122, -122, -123,
-124, -125, -125, -126, -126, -126, -127, -127, -127, -127, -127,
-127, -127, -126, -126, -126, -125, -125, -124, -123, -122, -122,
-121, -120, -118, -117, -116, -115, -113, -112, -111, -109, -107,
-106, -104, -102, -100, -98, -96, -94, -92, -90, -88, -85, -83,
-81, -78, -76, -73, -71, -68, -65, -63, -60, -57, -54, -51, -49,
-46, -43, -40, -37, -34, -31, -28, -25, -22, -19, -16, -12, -9, -6, -3
};
/*static const uint8_t ddsSineTable[256] PROGMEM = {
128,131,134,137,140,143,146,149,152,155,158,162,165,167,170,173, 128,131,134,137,140,143,146,149,152,155,158,162,165,167,170,173,
176,179,182,185,188,190,193,196,198,201,203,206,208,211,213,215, 176,179,182,185,188,190,193,196,198,201,203,206,208,211,213,215,
218,220,222,224,226,228,230,232,234,235,237,238,240,241,243,244, 218,220,222,224,226,228,230,232,234,235,237,238,240,241,243,244,
@ -145,7 +166,7 @@ static const uint8_t ddsSineTable[256] PROGMEM = {
10,11,12,14,15,17,18,20,21,23,25,27,29,31,33,35, 10,11,12,14,15,17,18,20,21,23,25,27,29,31,33,35,
37,40,42,44,47,49,52,54,57,59,62,65,67,70,73,76, 37,40,42,44,47,49,52,54,57,59,62,65,67,70,73,76,
79,82,85,88,90,93,97,100,103,106,109,112,115,118,121,124 79,82,85,88,90,93,97,100,103,106,109,112,115,118,121,124
}; };*/
#endif /* DDS_TABLE_LARGE */ #endif /* DDS_TABLE_LARGE */
class DDS { class DDS {