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LTC 2065 is not working between 2 V - 4 V power supply

Category: Hardware
Product Number: LTC 2065

Hello,
I'm having a problem with the LTC2065 operational amplifier design. I use a 3.3V supply as I show in the picture, and after boosting my input signal I make it oscillate at 1.8V using a 1.8V virtual ground.
Everything is normal until the low pass filter (U4) output. I see the signal I give from the input at the output with as much gain as I expected, and I use the same opamp in the high pass filter (U2), but here I get the wrong output signal. The strange thing is that when I give my supply signal a voltage of 4 V or above, my system works without any problems.
Below I give my circuit and signal outputs. How can I find a solution for my design, what am I missing?

Circuit 



Low pass output with 3.3 V supply (V2)



High pass output with 3.3 supply  (V2)


Low pass output with 5 V supply (V2)



High pass output with 5V supply  (V2)




Wrong picture
[edited by: atifkocak at 9:23 PM (GMT -4) on 12 Oct 2023]

Top Replies

    •  Analog Employees 
    •  Super User 
    Oct 3, 2023 +1 verified

    Hi  ,

    Good day. I tried simulating the frequency response of the circuit for 3.3 V and 5 V and observed that the gain response shifted to a much lower gain value for 3.3 V supply voltage. Since…

  • Hi  ,

    Good day. I tried simulating the frequency response of the circuit for 3.3 V and 5 V and observed that the gain response shifted to a much lower gain value for 3.3 V supply voltage. Since the input is approx. 15 Hz, I tried to focus on the gain of the circuit at this frequency. 

    This is for 3.3 V. Notice that the HP filter had a gain response of - 34.8 dB which would attenuate the output which could be the reason for your output. 

    This is for 5 V. The gain response is at 93 dB which is much higher than that with a supply of 3.3 V.

    I would recommend adjusting the value of R5 ( 7.5 MOhms) to 7.5 kOhms to change the gain of the circuit. This would shift the frequency response to a higher gain value and would amplify the output.