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Circuit with AD620: Wheatstone Bridge amplification

Category: Hardware
Product Number: AD620

Hi! I would like to know a few thing about an application that requires the use of the AD620 for amplifying signals from a full- wheatstone bridge with strain gauges.
I am using 350Ohms Strain gauges connected to the AD620 like shown in the photo. Also, I am driving the Ref Pin to a mid-voltage using a buffer, as required by the IC. In my board, there are a total of 4 AD620 (so it is possible to use 4 force sensors.). Can I use the output of the same LM358 to drive the Ref Pin in all AD620 chips? Or should I use one OpAmp for each sensor? The offset level should be the same for each w-bridge.

Also, should I use any resistor between the signal from the bridge and the AD620 inputs?

Thank you.

Circuit Diagram:

The VCC is 3v3 and this circuit is replicated 4 times in my current design. If it is possible to use only one LM358 for every AD620, it would significantly reduce my board design size. 

  • Hi pfu2,

    Good day!

    Unfortunately, we do not LM358. However, to answer your question regarding the reference terminal of AD620, you may use a single buffer amplifier to supply multiple AD620 vrefs since buffer amplifier will allow a low-impedance connection to the vrefs. You need to consider the sourcing capability of the opamp you will use. For this, you may consider ADA4807-1. This is a low-noise rail-to-rail amplifier, good for this type of application.

    Also, you may consider using voltage reference ICs instead of a buffer amplifier. Voltage reference ICs are specifically used for supplying reference terminals of other ICs. One voltage reference IC that you may consider is the LT6654.

    Regarding your supply voltages, 3.3V VCC is not possible for AD620. The supply range (+Vs to -Vs) should be from 4.6V to 36V. You may choose to supply the AD620 at 5V and your vref can be at 2.5V.

    You may use our Diamond Plot Tool to check for valid input voltages for our instrumentation amplifiers.

    I hope this helps.

    Best regards,