Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Problem with defining DNL of Nyquist ADC

Status
Not open for further replies.

neoflash

Advanced Member level 1
Joined
Jul 2, 2005
Messages
492
Helped
10
Reputation
20
Reaction score
2
Trophy points
1,298
Activity points
4,759
INL/DNL of Nyquist ADC

There is statement saying:

If DNL > 1LSB, there must be a missing code.

Why it is true? How many different definitions does DNL have?
 

Shaber_Mezbah

Newbie level 6
Joined
Oct 3, 2005
Messages
11
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,281
Activity points
1,386
INL/DNL of Nyquist ADC

If you apply one positive going ramp and check:

{code(i)-code(i+1)} in terms of lsb. then it should increase by 1-lsb. so, if you substruct 1-lsb from it then you get zero. it makes DNL(i)=0.

All definition has the same meaning, only diferent in approach.

for missing code(from positive ramp); if DNL<-1lsb.
then only you will miss your code.
 

neoflash

Advanced Member level 1
Joined
Jul 2, 2005
Messages
492
Helped
10
Reputation
20
Reaction score
2
Trophy points
1,298
Activity points
4,759
INL/DNL of Nyquist ADC

DNL < -1LSB should not imply missing code.

I think they do not have direct relationship. If bit (i) DNL is -1.5dB, bit (i+1) DNL is 1dB, bit (i+2) DNL is 0.5dB, then the total INL induced is zero and there is no missing code. Code (i+1), (i+2) is still there.
 

Shaber_Mezbah

Newbie level 6
Joined
Oct 3, 2005
Messages
11
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,281
Activity points
1,386
INL/DNL of Nyquist ADC

DNL is not defined in dB.!!!.
 

neoflash

Advanced Member level 1
Joined
Jul 2, 2005
Messages
492
Helped
10
Reputation
20
Reaction score
2
Trophy points
1,298
Activity points
4,759
INL/DNL of Nyquist ADC

sorry, should be LSB, typo...
 

maxwellequ

Full Member level 3
Joined
Jun 27, 2001
Messages
185
Helped
25
Reputation
50
Reaction score
13
Trophy points
1,298
Activity points
2,208
Re: INL/DNL of Nyquist ADC

The DNL it is the normalized deviation of the difference between two consecutive code transition levels, with respect to the ideal value, VLSB:
DNL(i)=(Vt[i+1]-Vt-VLSB)/VLSB=(Vt[i+1]-Vt)/VLSB-1
where Vt is the input voltage where the transition from code i-1 to i occurs.

Thus, when DNL=-1, we have Vt[i+1]=Vt, which means that code i does not exist -> missing code.

So, Shaber_Mezbah is right.

Rgds
 

    neoflash

    Points: 2
    Helpful Answer Positive Rating

Mline7

Member level 1
Joined
Dec 28, 2004
Messages
34
Helped
5
Reputation
10
Reaction score
4
Trophy points
1,288
Location
Marseille, FRANCE
Activity points
523
Re: INL/DNL of Nyquist ADC

DNL < -1LSB does not mean that a code is missing. But it implies that the converter is not monotonic. Which may be a serious matter in closed loop applications such as regulation.
 

sankudey

Full Member level 3
Joined
Sep 6, 2005
Messages
177
Helped
37
Reputation
74
Reaction score
11
Trophy points
1,298
Location
India
Activity points
3,515
Re: INL/DNL of Nyquist ADC

Hi,
In my view the definition is correct....although it is not the actual definition...but the definition implies this....you can go thru the folloing post ....a very good book...and hopefully convince on the matter....



may help you....

sankudey
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top