基于MAX5891 的差分輸出的測量方法簡介

VCODE是計算的DAC輸出電壓值。

下面的等式用于計算任意給定編碼的DNL：

DNLCODE(LSBs) = [VCODE - VCode-1 - VLSB]/VLSB(公式4)

其中

CODE是要計算的數字編碼。

VCODE是針對CODE計算的DAC輸出電壓值。

VCODE-1是針對CODE - 1計算的DAC輸出電壓值。

VLSB是公式2中計算的電壓值。

以下舉例說明利用MATLAB腳本計算MAX5889、MAX5890和MAX5891的線性度。每次計算都得到最小和最大DNL和INL誤差編碼和誤差值。實例還為所有編碼畫出了傳輸函數，得到INL和DNL。要求用戶輸入前面表格中所列出編碼的電壓測量值。必須按照所列順序輸入數值。

計算16位線性度的MATLAB腳本

function Lin16(Measurements)

%Calculate INL and DNL of a 16-bit device with a 5-4-3-4 segmentation architecture

% DacCodes is the range of possible input data to the 16-bit DAC

DacCodes=[0:65535]’;

%VOUT for each code is calculated from the measured points

%create a VOUT variable and fill it with zeros

VOUT=zeros(size(DacCodes));

%The first measurement is the zero-scale point, or code (0x0000)

ZS=Measurements(1);

VOUT(1)=ZS;

%The last measurement is the full-scale point, or code (0xFFFF)

FS=Measurements(length(Measurements));

VOUT(65536)=FS;

%Midscale is stored at position 43 of the input data array

MS=Measurements(43);

%The device has four segmentation levels

Segments=4;

%The decimal values for the LSB codes are 1, 2, 4 and 8

Seg1Codes=[1;2;4;8];

%The voltages for the LSBs are in positions 2-5 of the input array

for i=1:4

Seg1V(i)=Measurements(i+1)-MS;

end

%The second level of segmentation is controlled with input codes 16 through

%112 in steps of 16. Create the code array and fill the measurements for

%this segmentation level

Seg2Codes=[16:16:16*7]’;

for i=1:7

Seg2V(i)=Measurements(i+5)-MS;

end

%Segmentation level 3 uses input codes 128 through 1920 in steps of 128.

%Create the code array and fill the measurements array.

Seg3Codes=[128:128:128*(2^4-1)]’;

for i=1:15

Seg3V(i)=Measurements(i+12)-MS;

end

%Segmentation level 3 uses input codes 2048 through 63,488 in steps of 2048.

%Create the code array and fill the measurements array.

Seg4Codes=[2048:2048:2048*(2^5-1)]’;

for i=1:31

Seg4V(i)=Measurements(i+27)-ZS;

end

%The endpoints have been defined, now fill in the voltages for the

%remaining points of the DAC transfer function.

for i = 2:65535

targetcode=i-1;

VOUT(i)=ZS;

for s=31:-1:1

if Seg4Codes(s)=targetcode

targetcode=targetcode-Seg4Codes(s);

VOUT(i)=VOUT(i)+Seg4V(s);

s=0;

end

end

for s=15:-1:1

if Seg3Codes(s)=targetcode

targetcode=targetcode-Seg3Codes(s);

VOUT(i)=VOUT(i)+Seg3V(s);

s=0;

end

if targetcode==0

s=0;

end

end

for s=7:-1:1

if Seg2Codes(s)=targetcode

targetcode=targetcode-Seg2Codes(s);

VOUT(i)=VOUT(i)+Seg2V(s);

s=0;

end

if targetcode==0

s=0;

end

end

if targetcode==0

s=0;

end

for s=4:-1:1

if Seg1Codes(s)=targetcode

targetcode=targetcode-Seg1Codes(s);

VOUT(i)=VOUT(i)+Seg1V(s);

end

end

end

%Plot the transfer function

figure(1)

plot(DacCodes, VOUT);

xlabel(‘DAC Input Code’);

ylabel(‘Measured Voltage’);

axis([0 65536 -1.1 1.1]);

title(‘DAC Transfer Function’);

set(gca,’XTick’,0:16384:65536)

%Calculate the linearity

LSB=(max(VOUT)-min(VOUT))/65535;

INL(1)=0;

DNL(1)=0;

for i=2:65536

INL(i)=(VOUT(i)-(VOUT(1)+(i-1)*LSB))/LSB;

DNL(i)=(VOUT(i)-VOUT(i-1)-LSB)/LSB;

end

%Plot INL

figure(2)

plot(DacCodes, INL);

title(‘DAC Integral Linearity’);

xlabel(‘DAC Input Code’);

ylabel(‘INL (LSBs)’);

axis([0 65536 min(INL)*1.1 max(INL)*1.1]);

set(gca,’XTick’,0:16384:65536)

%Plot DNL

figure(3)

plot(DacCodes, DNL);

title(‘DAC Differential Linearity’);

xlabel(‘DAC Input Code’);

ylabel(‘DNL (LSBs)’);

axis([0 65536 min(DNL)*1.1 max(DNL)*1.1]);

set(gca,’XTick’,0:16384:65536)

txtstr=sprintf(‘INL MAX = %f’, max(INL));

disp (txtstr);

txtstr=sprintf(‘INL MIN = %f’, min(INL));

disp (txtstr);

txtstr=sprintf(‘DNL MAX = %f’, max(DNL));

disp (txtstr);

txtstr=sprintf(‘DNL MIN = %f’, min(DNL));

disp (txtstr);

16位腳本產生的曲線