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

OPAMP: General question about chosing resistors

Status
Not open for further replies.

Juja

Newbie level 3
Joined
May 15, 2015
Messages
4
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
44
Dear forum,

just a simple (?) beginner question:

What is the difference e.g. having a differential opamp circuit with v=10 and using

1) 10k-resistor and 100k-resistor (OPAMP_1.png)

OR

2) 1k-resistors and 10k-resistor (OPAMP_2.png)

Thanks so far!
 

Attachments


SunnySkyguy

Advanced Member level 5
Joined
Sep 26, 2007
Messages
6,743
Helped
1,675
Reputation
3,348
Reaction score
1,643
Trophy points
1,413
Location
Richmond Hill, ON, Canada
Activity points
50,727
same gain, difference is input impedance and output drive current

Iout for rail-rail OP Amps is small ( due to high RdsON of internal CMOS output stage) so 10k may not reach 100% both rails if reference is Vbat/2, so >> 10k feedback R is preferred for low Iout.

But if R values are too high, then input bias current offset may cause a Vin offset which may be significant, espec. if using high ratio gains >>10 like 1k~10k
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,817
Helped
1,738
Reputation
3,478
Reaction score
1,337
Trophy points
1,393
Location
Germany
Activity points
39,031
Dear forum,
just a simple (?) beginner question:
An answer to your question was given above.
However, as you are a beginner: Are you aware that using only one single supply voltage (s shown in your diagrams) imposes some severe operational restrictions?
The classical opamp application requires dual supply (+/- voltages).
 

godfreyl

Advanced Member level 5
Joined
Apr 18, 2012
Messages
1,981
Helped
632
Reputation
1,266
Reaction score
624
Trophy points
1,393
Activity points
12,776
Another consideration may be noise. If you make the resister values 10 times higher, the Johnson noise will be 10dB higher. This only matters if you want very low noise obviously, and then you need to use a low-noise opamp otherwise the opamp noise will be higher than the resistor noise anyway.
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top