signal-conditioning circuit using an instrumentation amplifier

Question

Dear sir/Ma'am, 
 We want to design the front end of a signal-conditioning circuit using an instrumentation amplifier. We are using an (AD8226) instrumentation amplifier so that the common mode noise is rejected at the front end. 
 The differential input voltage to the op-amp will be +2V or -2V when it is DC and 4Vpk-pk if signal is 14kHz AC sin wave. It should be noted that at any given time, the input will be any one i.e. +2V or -2V or 4Vpk-pk. The below figure shows the typical connection which will be used in the application. 
 INSTRUMENTATION AMPLIFIER USED: AD8226 
 POWER SUPPLY TO THE AMPLIFIER: SINGLE SUPPLY 5V 
 GAIN: 1 
 REFERANCE VOLTAGE: 2.5V 
 INPUT TO OP-AMP: DIFFERENTIAL INPUT 
 Querry: When the differential Input to the op-amp is 2VDC the expected output is 4.5V but we are getting 4.13V 
 which can be observed in the circuit, please correct us if we are wrong. If so, please suggest a suitable instrumentation amplifier for our application. we eagerly await your recommendation

GLADION · Accepted Answer

Hi ANG162 , 
 
 Good day. Is adjusting the supply range allowable for your application? It seems that the current configuration is not within the operating range which could explain the measurement you are getting. See below the simulation for a Vref of 0 V. Here you can observe that there is already a limitation for a 4 Vpk-pk wave. 
 
 The diamond plot tool shows that the configuration is not operating within the supply limits. Please see the below figure: 
 
 To address this, I would recommend increasing the supply range. Instead of having a 5 V supply, I suggest you use a +/- 5 V supply range to extend the supply range. 
 
 I hope this helps. 
 Regards, Gilbeys)

Arsol · Answer

Hi ANG162 
 
 Thank you for reaching out and sharing this inquiry with us. 
 
 Can you modify some of your circuit connections, similar to the one we made in the simulation below? 
 Where IN- is connected to GND. This circuit will result in Out = 4.5V. 
 
 GLADION 
 Thanks,

ANG162 · Answer

Thanks for the reply. In our application the input section, should be symmetrical and hence we are using the instrumentation amplifier in differential mode. The input voltage of 26.3V will be applied in two different configuration as shown below. Hence single ended is not suitable for our application. Please suggest a suitable circuit for our application 
 Configuration: 01 
 
 Configuration: 02

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signal-conditioning circuit using an instrumentation amplifier

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