Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic 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.

Register Log in

Common mode voltage significance.

Status
Not open for further replies.

Rahul Soni

Member level 1
Joined
Aug 24, 2014
Messages
41
Helped
0
Reputation
0
Reaction score
0
Trophy points
6
Activity points
292
What is the significance of common mode voltage(CMV)?
In the datasheets, common mode voltage is given with the differential voltage.
What is the use of common mode voltage. What will be the effects if we don't consider CMV. ?

thanks in advance :)
 

crutschow

Advanced Member level 5
Joined
Feb 22, 2012
Messages
3,750
Helped
896
Reputation
1,790
Reaction score
875
Trophy points
1,393
Location
L.A. USA Zulu -8
Activity points
21,115
You don't "use" common-mode voltage, it is just the DC voltage that's common to both halves of a differential signal.
Thus you could have a 1mVac differential signal that's riding on a 3V common-mode DC level.
Differential amplifiers are rated as to the common-mode voltage they can tolerate on their inputs while still operating properly, so you must be sure the input signal stays within those limits.
If you do, then the differential signal will be amplified but the common-mode signal will be ignored (rejected).
Since no amplifier is perfect the amplifier spec will list the rejection value for the common-mode voltage (how much of the common-mode voltage appears at the output). Typically this value is very small (>80dB at DC)
So called rail-to-rail input op amps can operate with a common-mode voltage anywhere between the positive supply rail and the negative supply rail.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
18,124
Helped
4,060
Reputation
8,120
Reaction score
3,982
Trophy points
113
Activity points
119,562
Hi,

the term "common mode voltage" is used for many applications.

Please tell us what application is in your mind.

Klaus
 

Rahul Soni

Member level 1
Joined
Aug 24, 2014
Messages
41
Helped
0
Reputation
0
Reaction score
0
Trophy points
6
Activity points
292
Hi,

the term "common mode voltage" is used for many applications.

Please tell us what application is in your mind.

Klaus
While using ICS85104I fan out buffer, I found this table
Screenshot.jpg

I am unable to understand why this Vcm is provided and where will it be used?

Thanks in advance.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
18,124
Helped
4,060
Reputation
8,120
Reaction score
3,982
Trophy points
113
Activity points
119,562
Hi,

VPP says the difference between the two inputs must not be more than 1.3V.

But referenced to GND both inputs may be near GND and also near VCC. (Common mode).

With differential inputs the absolute voltage level referenced to GND is not that important.
If CLK0 is at 0.8V and nCLK0 is at 0.5V, then the output is HIGH.
If CLK0 is at 1.5V but nCLK0 is at 1.8V, then the output is LOW, although now the CLK0 level is much higher than before.

See both inputs as comparator inputs. CLK0 is the noninverting input, nCLK0 is the inverting input.

Klaus
 
Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top