Continue to Site

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.

Register Log in

ADC -- How to measure negative voltage

Status
Not open for further replies.
F

funghome

Newbie level 4
Joined
Oct 15, 2006
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,323
adc negative voltage

I have an ADC LTC2410. How can it measure negative voltage with respect to ground, but not IN-?
IN- will be grounded in measuring.
Thanks.
 

negative voltage adc

Hi,
Either you need to invert the negative signal and apply, or, you can level shift the signal around half Vcc, apply it to IN+ and connect IN- to half Vcc. Vref in the second case should be Vcc and the shifted signal range to be adjusted to be within 0 to 5V.
Normally, if the signal is floating, you should ground the -ve lead and connect the positive lead directly to IN+ without any problem.

Regards,
Laktronics
 

adc negative

laktronics said:
Hi,
Either you need to invert the negative signal and apply, or, you can level shift the signal around half Vcc, apply it to IN+ and connect IN- to half Vcc. Vref in the second case should be Vcc and the shifted signal range to be adjusted to be within 0 to 5V.
Normally, if the signal is floating, you should ground the -ve lead and connect the positive lead directly to IN+ without any problem.

Regards,
Laktronics
Click to expand...
Invert the negative signal need two resistor and opamp. I think it will lost some precision.
Can you draw a circuit digram to explain more how to shift the input signal half Vcc. Input signal is bipolar voltage and common ground with ADC.
Thanks.
 

adc negative input

Hi,
As you have rightly pointed out, any tampering with input is likely to affect precision and introduce additional noise. In the first place it appears the chip is not designed to handle negative inputs.
If your input voltage range is +/-5V, you may use two equal metal film resistors of say, 10kvalue, connected in series, with Vref(5V) connected to one end and Vin connected to the other end. Connect the mid point of the resistors to IN+. To IN- connect the mid point of another pair of series connected equal resistors with their free ends connected to Vref and ground. You have to ensure that all the four resistors have matching characteristics.

Regards,
Laktronics
 

    F

    funghome

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top