From 5d1cff57f9f5acd740a8b5f8c941beefdcc00176 Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Sun, 28 Jun 2020 16:42:21 +0200
Subject: sw: configure si5351

---
 freqplan.py | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 freqplan.py

(limited to 'freqplan.py')

diff --git a/freqplan.py b/freqplan.py
new file mode 100644
index 0000000..8ad520f
--- /dev/null
+++ b/freqplan.py
@@ -0,0 +1,66 @@
+#!/usr/bin/env python3
+
+from fractions import Fraction
+from math import floor
+
+xtal = 25
+
+print()
+print("# 160MHz and 4.915 MHz on PLLa")
+
+PLLa = xtal * 32
+print(f"PLLa = xtal * 32 = {PLLa} MHz")
+
+# x/y = a + b/y
+# a = floor(x/y)
+# b = x - (a * y)
+
+f1 = 116
+a = floor(PLLa / f1)
+b = PLLa - (a * f1)
+div1 = Fraction(b, f1)
+print(f"CLK1: f1 = PLLa / ({a} + {div1.numerator} / {div1.denominator}) = {f1}")
+
+f2 = 4.91521
+a = floor(PLLa / f2)
+b = PLLa - (a * f2)
+div1 = Fraction(round(b * 10000), round(f2 * 10000))
+print(f"CLK2: f2 = PLLa / ({a} + {div1.numerator} / {div1.denominator}) = {f2}")
+
+
+print()
+print("# VFO between 23 and 25 MHz on PLLb")
+
+def calculate(frequency):
+    divider = floor(900000000 / frequency) # Calculate the division ratio. 900,000,000 is the maximum internal
+
+    if divider % 2:
+        divider -= 1 # Ensure an even integer division ratio
+
+    pllFreq = round(divider * frequency) # Calculate the pllFrequency: the divider * desired output frequency
+
+    xtalFreq = xtal * 1000000
+    mult = floor(pllFreq / xtalFreq) # Determine the multiplier to get to the required pllFrequency
+
+    l = pllFreq % xtalFreq # It has three parts:
+
+    f = floor(l) # mult is an integer that must be in the range 15..90
+    denom = 1048575
+    f *= denom # num and denom are the fractional parts, the numerator and denominator
+    f /= xtalFreq # each is 20 bits (range 0..1048575)
+
+    num = floor(f) # the actual multiplier is  mult + num / denom
+    return (divider, mult, num, denom)
+
+vfo = 23000000
+for i in range(10):
+    divider, mult, num, denom = calculate(vfo)
+
+    PLLb = xtal * 1000000 * (mult + num/denom)
+
+    freq = PLLb / divider
+
+    delta = vfo - freq
+
+    print(f"CLK0: VFO {vfo}, PLLb = xtal * ({mult} + {num} / {denom}) = {PLLb}, PLLb / {divider} = {freq}, delta = {delta:.03} Hz")
+    vfo += 100000
-- 
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