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lin_method_dem.py
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lin_method_dem.py
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""Dynamic element matching.
@author: Arnfinn Aas Eielsen
@date: 07.03.2024
@license: BSD 3-Clause
"""
import numpy as np
from numpy import matlib
import math
from scipy import signal
def ssb(c, d):
"""
Segmenting switching block.
c
input
d
randomiser
"""
# d = np.random.randint(2)
if c % 2: # c is odd
s = 0
else: # c is even
if d:
s = 1
else:
s = -1
t = (c - 1 - s)/2
b = 1 + s
return int(t), int(b) # top switch, bottom switch
def nssb(c, d):
"""
Non-segmenting switching block.
c
input
d
randomiser
"""
# d = np.random.randint(2)
if c % 2: # c is odd
if d:
s = 1
else:
s = -1
else: # c is even
s = 0
t = (c - s)/2
b = (c + s)/2
return int(t), int(b) # top switch, bottom switch
def dem(X, Rng, Nb):
"""
X
input signal
Rng, N
quantiser params. (for re-quantisation and code generation)
"""
# DEM code input range
M = 2*(2**Nb - 1)
cmin = 2**(Nb-1) - 1
cmax = M - 2**(Nb-1) + 1
Qseg = Rng/(cmax-cmin) # segmented step-size (LSB)
cin = 2**(Nb-1) # when input it bipolar an offset is needed
# DEM mapping from output segment weights to codes
Ks = 2**np.arange(0, Nb).astype(int)
Ks = matlib.repmat(Ks, 2, 1)
# Store codes
C = np.zeros((2, X.size)).astype(int) # individual DAC codes (1 ch. per row)
Ci = np.zeros(X.size).astype(int) # initial codes
#Csum = np.zeros(X.size).astype(int) # sum of segmented codes (verification)
from lin_method_dem import ssb, nssb
for i in range(0, X.size):
w = X[i]
# Re-quantizer for segmented DAC
qs = math.floor(w/Qseg + 0.5) + cin # mid-tread
# Generate DEM codes
c = qs + cmin
Ci[i] = c
# DEM
Ss = np.zeros((2, Nb)).astype(int) # segment switching block results
c1 = c # initial switching block input
# random switching sequence
d = np.random.randint(2, size=2*Nb-1) # white
for j in range(0, Nb-1):
Sst, Ssb = ssb(c1, d[2*j]) # segmenting switching
c1 = Sst # save for next iteration
c2 = Ssb # feed to next switching block
Snt, Snb = nssb(c2, d[2*j+1]) # non-segmenting switching
Ss[0, j] = Snt
Ss[1, j] = Snb
c2 = Sst
Snt, Snb = nssb(c2, d[-1]) # non-segmenting switching
Ss[0, Nb-1] = Snt
Ss[1, Nb-1] = Snb
C[:, i] = np.sum(Ss*Ks, 1)
#Csum[i] = np.sum(C[:, i]) # (verification)
return C