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

[SOLVED] The concept virtual ground in op-amps

Status
Not open for further replies.

ashugtiwari

Full Member level 4
Joined
Dec 12, 2008
Messages
218
Helped
45
Reputation
90
Reaction score
44
Trophy points
1,308
Activity points
3,310
Hi All,
In Op-Amps what actually the concept virtual ground? Is it only considered in Op-Amps based design or in other descrete design too? What is its significance.

Please reply.
Thanks in advance
Ashutosh
 

Mehdi1357

Member level 2
Joined
Jan 18, 2008
Messages
47
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,286
Location
the Earth
Activity points
1,651
Re: Virtual ground

In the theory of electrical networks, a virtual ground (or virtual earth) is a node of the circuit that is maintained at a steady reference potential, without being connected directly to the reference potential. In some cases the reference potential is considered to be that of the surface of the earth, and the reference node is called "ground" or "earth" as a consequence.

See, for more information

http://en.wikipedia.org/wiki/Virtual_ground
 

ashugtiwari

Full Member level 4
Joined
Dec 12, 2008
Messages
218
Helped
45
Reputation
90
Reaction score
44
Trophy points
1,308
Activity points
3,310
Re: Virtual ground

Thanks for info Mehdi
Can you please tell me how the concept used in op-amp design and what is its significance in terms of virtusl ground or how can I use this concept in op-amp desingning.

Ashutosh
 

dick_freebird

Advanced Member level 5
Joined
Mar 4, 2008
Messages
7,127
Helped
2,088
Reputation
4,180
Reaction score
1,934
Trophy points
1,393
Location
USA
Activity points
57,176
Virtual ground

As an example, a single-ended op amp configured as
an inverting amp (or integrator, differentiator, etc.)
would often tie the + terminal to GND (perhaps via a
resistor, or not). The - terminal is servoed by the amplifier
output via the feedback network to match the + terminal
potential, thus it is "virtual" as opposed to "explicit" even
though (at rest) the two potentials may be identical. The
impedance and current loops, however, are certainly not.
 

Vabzter

Member level 1
Joined
Jan 18, 2007
Messages
33
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,286
Activity points
1,492
Re: Virtual ground

Hi,
In case of a differential amplifier when you give pure differential signal to the inputs then one voltage on the gate is increasing and the voltage on the other gate is decreasing. The point where the sources of both the transistors are connected remains same. Hence you can assume that a vitual ground is present. Hence to analyze this circuit you can break the circuit in two halves and use half circuit analysis as all the other components and connections are same. This simplifies the analysis to a large extent as now you have a common source stage to analyze.

Hope this helps
BR
Vabzter
 

Mehdi1357

Member level 2
Joined
Jan 18, 2008
Messages
47
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,286
Location
the Earth
Activity points
1,651
Re: Virtual ground

ashugtiwari said:
Can you please tell me how the concept used in op-amp design and what is its significance in terms of virtusl ground or how can I use this concept in op-amp desingning.

Ashutosh

the virtual ground is a node that have extremely little voltage swing at any conditions.
there are Ac,Dc or both virtual grounds.you should distinct the type of virtual ground before analysing a circuit.
remember in any negative feedback circuit with op amp there is one virtual ground at least.
usisng virtual ground concept will help you to solve op_amp circuits and reduces the calculation costs.
see the following articles:
http://tangentsoft.net/elec/vgrounds.html
www.colorado.edu/physics/phys3330/PDF/Experiment5.pdf
 

snafflekid

Full Member level 4
Joined
May 9, 2007
Messages
214
Helped
31
Reputation
62
Reaction score
8
Trophy points
1,298
Location
USA
Activity points
2,644
Re: Virtual ground

Yeah. In the idealized concept of negative feedback op-amp circuits, the voltage that is applied to one input will be forced to appear on the other input by negative feedback. In a non-inverting op-amp configuration, the positive input is often grounded, so the feedback forces the negative input to ground. It is not actually ground, but conceptualizing that the negative input is virtually grounded lets you easily work out the currents flowing in the feedback resistors and whatever else.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top