LMX2820: Spur-b-gone Algorithm code

Ian,

I am glad that you like the Spur-b-Gone code.  The general strategy is to avoid integer boundary spurs as a first priority. But also, when you are close to, but not exactly near a fraction of 1/2, you also get higher spurs, although less severe.

You can open the LMX2571.py file and find this code as well.

Also realize that for any TICSPro part, you can mouse over boxes and see the name.

For instance "Fosc_FREQ" is the OSCin box.  "Fosc_FREQ.dValue" is this value expressed as a double

This is in python, but the copy and paste ruined the indent, but I think that you can hopefully get the idea.

Regards,
Dean

def btn_SpurBGone_Update():
Fosc=Fosc_FREQ.dValue
Fpd = Fpd_FREQ.dValue
Fvco=Fvco_FREQ.dValue
Fnum=flexPLL_NUM.iValue
OldFden = flexPLL_DEN.iValue
OldMult = flexMULT.iValue


OldTotalR = int(Fosc * OldMult / Fpd)

MultInMin = 10
MultInMax = 30
MultOutMin = 60
MultOutMax = 130

FpdMin = Fpd * 0.7
FpdMax = Fpd * 1.4
if (FpdMax > 140):
FpdMax = 140

BestIBSMetric = 0.00000000001

FpdMin = Fpd * 0.7
FpdMax = Fpd * 1.4
if (FpdMax > 140):
FpdMax = 140

BestIBSMetric = 0.00000000001
FoundBest = False

for Mult in range(1,16):
if (FoundBest==True):
break;
if (Mult==1):
PLL_R_PRE_min = 1
PLL_R_PRE_max = 1
else:
PLL_R_PRE_min = int(math.ceil(Fosc / MultInMax))
if (Fosc > MultInMax*PLL_R_PRE_min):
PLL_R_PRE_min = PLL_R_PRE_min + 1

PLL_R_PRE_max = int(Fosc / MultInMin)
if (Fosc / PLL_R_PRE_max < MultInMin):
PLL_R_PRE_max = PLL_R_PRE_max - 1

for PLL_R_PRE in range(PLL_R_PRE_min,PLL_R_PRE_max+1):
MultOut = Fosc / PLL_R_PRE * Mult
if (Mult==1) or ((MultOut > MultOutMin - 0.0001) and (MultOut < MultOutMax - 0.0001) ):
for PLL_R in range(1,10):
Fpd = Mult * Fosc / (PLL_R_PRE * PLL_R)

if (Fpd<FpdMin):
break;

if (Fpd<FpdMax):
PLL_N = 2 * int(0.5+ 1.0*math.floor(Fvco / Fpd / 2) )

IBS = math.fabs(Fvco - PLL_N * Fpd)
if (IBS > math.fabs(Fpd - IBS) ):
IBS = math.fabs(Fpd - IBS)

IBS2 = math.fabs(Fpd / 2 - IBS)


if (IBS < IBS2):
IBSMetric = IBS
else:
IBSMetric = IBS * (40 * IBS2) / (IBS + 40 * IBS2 + 0.000000000001)


if (IBS < 0.000001):
# Best Case Scenario, integer Channel
BestIBS = 0
BestMult = Mult
BestPreR = PLL_R_PRE
BestPLL_R = PLL_R
BestFpd = Fpd
BestIBS2 = IBS2
BestIBSMetric = IBS2
FoundBest = True
elif (IBS2 > 0.000001) and (IBSMetric > BestIBSMetric):
# Decide based on weighted metric
BestIBS = IBS
BestMult = Mult
BestPreR = PLL_R_PRE
BestPLL_R = PLL_R
BestFpd = Fpd
BestIBS2 = IBS2
BestIBSMetric = IBSMetric


# Decide if it is necessary to update the fractional Denominator
Fden = OldFden

if (OldMult % BestMult > 0):

# Find the Denominator of the original fraction in reduced form
i=2
while (i<math.sqrt(Fden*1.0) ):
if (Fnum%i==0) and (Fden%i==0):
Fden = Fden/i
Fnum = Fnum/i
else:
i=i+1

# X and Y are Mult* x TotalR
X = BestMult * OldTotalR
Y = OldMult * BestPreR * BestPLL_R


while (i<math.sqrt(X*1.0) ):
if (X%i==0) and (X%i==0):
X = X/i
Y = Y/i
else:
i=i+1

# Now find the smallest possible simplified denominator
if (X*Fden > 16777215):
Fden = OldFden
else:
Fden = Fden*X

# Now try to Scale Fden back to something close to the original value
GCD = int(0.5+OldFden*1.0 / Fden)
if (GCD<1):
GCD=1
Fden=Fden*GCD

flexPLL_R_PRE.iValue = BestPreR
flexMULT.iValue=BestMult
flexPLL_R.iValue=BestPLL_R
Fpd_FREQ.dValue=BestFpd
flexPLL_DEN.iValue=Fden
flexPLL_NUM.iValue=Fnum
Fvco_FREQ_Update()
if (GetActivePLL()==1):
PLL_R_PRE_F1.iValue=flexPLL_R_PRE.iValue
MULT_F1.iValue=flexMULT.iValue
PLL_R_F1.iValue=flexPLL_R.iValue
Fpd_F1_FREQ.dValue=Fpd_FREQ.dValue
PLL_N_F1.iValue=flexPLL_N.iValue
PLL_NUM_F1.iValue=flexPLL_NUM.iValue
PLL_DEN_F1.iValue=flexPLL_DEN.iValue
Fvco_F1_FREQ.dValue=Fvco_FREQ.dValue
else:
PLL_R_PRE_F2.iValue=flexPLL_R_PRE.iValue
MULT_F2.iValue=flexMULT.iValue
PLL_R_F2.iValue=flexPLL_R.iValue
Fpd_F2_FREQ.dValue=Fpd_FREQ.dValue
PLL_N_F2.iValue=flexPLL_N.iValue
PLL_NUM_F2.iValue=flexPLL_NUM.iValue
PLL_DEN_F2.iValue=flexPLL_DEN.iValue
Fvco_F2_FREQ.dValue=Fvco_FREQ.dValue