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AD8235/AD8237 Correct biasing approach

How do I know that I'm biasing the AD8235/AD8237 correctly?

[edited by: ESanz at 7:32 AM (GMT -4) on 28 Sep 2021]
  • The AD8235 and AD8237 are instrumentation amplifiers (in-amps) and these low power devices are great for a breadth of different applications that include pressure, strain or even temperature sensing.  

    The AD8235 and AD8237 just like many in-amps  have a reference input pin that can be used to apply a bias voltage to set the output  of the in-amp to the correct level for the downstream circuitry. The ability to adjust the output of the in-amp will ensure the complete output signal swing is use.    For 3 op-amp in-amps and 2 op-amp in-amps like the AD8235, internal nodes can saturate if not biased correctly.  When configuring the in-amp for your design it is important to note that the output signal of the in-amp is dependent on the input signal, reference voltage, the gain as well as the power supply voltage and is typically characterized by the "Diamond Plot". 

     The AD8237 is an indirect current mode in-amp and has built in capability to eliminate the Diamond Plot making it much easier to bias. 

    As part of the precision studio toolkit from analog devices, you will find the Instrumentation Amplifier Diamond Plot Tool (link here) There is an excellent article in analog dialogue that unveils the secrets of the diamond plot tool found here, so have a read before diving into your design as it highlights some of the key considerations when configuring the in-amp in your design. The tools supports all of ADIs instrumentation amplifiers, so you will find both the AD8235  and AD8237 supported as well as many of our other instrumentation amplifiers.