# Current to voltage conversion with level shifting for the current

#### Ajay1989

Joined Feb 1, 2016
6
Hi Guys and Gals,

I am working with a sensor which outputs current in the range of +/- 72 mA.
I want to amplify (1.1976mA to 1.2024 mA) of the sensor output to (0 to 5V).

I am comfortable with current to voltage amplification but I am not sure how to do level shifting for the current i.e. 1.1976 mA corresponds to 0V and 1.2024 mA corresponds to 5V.

What I was thinking was, to connect the output from the sensor to a 1.1976 mA current sink (so that my 1.1976 mA to 1.2024 mA becomes 0 to 4.8 uA), and then apply 10^6 amplification using op-amp transimpedence amplifier. But I can not find any more information if this can be done.
Any seniors could shed some light if this can work? Or is there any other simpler way to achieve this?

Thank you in advance and please let me know if you need any more clarification from my side

Regards
Ajay

#### PeterCoxSmith

Joined Feb 23, 2015
148
Take a look at the instrumentation amplifier AD623. Apply a reference of 2.5V and the output will swing from 0 to 5v, centred on 2.5V, with an input scaled to +/-0.5V and a gain of 5.

#### Ajay1989

Joined Feb 1, 2016
6
AD623 will very well work if the output from the sensor is voltage (please correct me if I am wrong)

But my sensor generates +/- 72 mA and I have to extract 1.976 to 1.204 mA and amplify to 0 to 5V.

Thanks
Ajay

#### PeterCoxSmith

Joined Feb 23, 2015
148
AD623 will very well work if the output from the sensor is voltage (please correct me if I am wrong)

But my sensor generates +/- 72 mA and I have to extract 1.976 to 1.204 mA and amplify to 0 to 5V.

Thanks
Ajay
use a resistor to convert current to voltage, calculate the resistance using ohm's law to scale +/-72mA to +/-0.5V...
R=0.5/0.072...6.94R...nearest value is 6.98R 0.1% tolerance.

#### Bordodynov

Joined May 20, 2015
2,885
See

#### Ajay1989

Joined Feb 1, 2016
6
Dear Bordodynov,

Thank you very much for your diagram. I assume I1 you drew is current sink of 1.2 mA. And I understood the 1 stage amplification circuit.
But I still have couple of doubts.

1. What is the use of R2, R3, U4 and BAT54S in this circuit
2. How do we realize 1.2mA current sink in actual circuit i.e. how to realize I1. I saw one sample design and is attached here. Will this work?

Thank you

Ajay

#### dannyf

Joined Sep 13, 2015
2,197
I would add it. Analog solutions are dicy, as the resolution is high.

An act with 20x gain plus Pam can do this easily, in a 8dip package.

#### Ajay1989

Joined Feb 1, 2016
6
I would add it. Analog solutions are dicy, as the resolution is high.

An act with 20x gain plus Pam can do this easily, in a 8dip package.
Thank you Danny for the reply. But I didn't understand your explanation here. Would you be able to elaborate a bit more?

Thank you
Ajay

#### Bordodynov

Joined May 20, 2015
2,885
On the twin Schottky diode limiter made. This protects the input of the amplifier. When operating in the linear range of the amplifier at the inverting input voltage is substantially zero. Therefore there is no need for precision current generator! Current generator can be replaced by a resistor. Used reference diode napyazheniem ~ 1.22V. For example LM4041-1.2, ZXRE125. With stable voltage across the resistor goes stable current. For the flowing currents of the current scheme is necessary to turn the resistor. It is also necessary to add an inverting amplifier. What is the current direction you?
Current resistor I have divided into two parts. This is the usual resistor and multi-turn potentiometers.
If you wish to limit the output voltage range (0V-5V), you'll need to add a precision limiter with operational amplifiers.

Last edited:

#### Ajay1989

Joined Feb 1, 2016
6
Thank you so mucj Bordodynov for your explanation.
Could you please share the .asc file for Ltspice IV ?

Thank you once again

Ajay

#### Bordodynov

Joined May 20, 2015
2,885
Get scheme and another. And many models of AD.

#### Attachments

• 107.3 KB Views: 2

#### Ajay1989

Joined Feb 1, 2016
6
Get scheme and another. And many models of AD.
Thank you for the files.
Could you also share the models for BAT54S, ShuntRef and Pot. When I opened the file it was showing error as shown in the pic below.

Thank you
Ajay

#### Bordodynov

Joined May 20, 2015
2,885
I am sorry. Replace standard.dio my file.

#### Attachments

• 262.3 KB Views: 2