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EMG circuit simulation, TINA - Operating point not found

Usama Imtiaz
Prodigy 105 points

Other Parts Discussed in Thread: INA333

Hi,

I've been trying to find the transfer function of my circuit. I am not very familiar with TINA. Though my actual circuit has some more modules, in this circuit, I removed the RLD circuitry, as well as an opamp-regulated reference voltage (replaced by 1.5V battery), Also I removed all the supply bypass capacitors. 

For the circuit, if I disconnect the INA333 from the Low pass filter (Just before R10), I can see the AC Transfer characteristic. But if they are connected, TINa gives me an error: Operating point not found U3.D17, which tells me it's having some issue with the Low pass filter, but I can't seem to figure out what. I've tried changing some Analysis parameters but haven't found any solution. I've attached the schematic file, and will be very grateful for your help.

 

Regards

Usama

 

6560.Final EMG sim.zip

  • 0
    Genius 5430 points

    Usama;

    Here is how I made it work-- add a 50M resistor from each INA333 input to ground and change the circuit to operate on +/-1.5V bipolar supplies instead of a single +3V supply.

    I can't explain why the circuit doesn't converge on a single supply-- sorry.

  • 0 in reply to Neil Albaugh
    Prodigy 105 points

    Hi,

    Thanks for your help, I don't want to add the 50M resistors as I've already implemented the circuit on PCB and want to check it's characteristics.

    Also, I'm afraid it will affect the AC Coupling and CMRR.

     

    The bipolar supply works! Actually I implemented my circuit with a single supply using a 3V Li battery.

    But just using bipolar batteries to get the same equivalent shifts (I had to replace all grounds with -1.5V and so on), it finally works! Thanks