Negative and positive voltages with LTC1403

Hi

Im new here and also electronics ;). I need to measure +/- 3.3V signal. I usually use microcontollers with level shifter but now I need some more precise ADC. I picked LTC1403. How can I measure negative voltages with differential input? Do I need level shifter and IN connect to ground? Or to minus of my of my power supply? Its my first time with external ADC.

Before signal I have some filters.

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  • If you can use the LTC1403-1, an easy solution is to use a fully differential amplifier like the ADA4945 between your filter circuit and the ADC input. Use the same +/-3V supplies for the ADA4945. Use figure 104 of the ADA4945 data sheet and connect VOCM to 1.5V and use 4.75k for RG and 1.96k for Rf. To minimize noise you may want to add an RC filter between the ADA4945 outputs and LTC1403-1 inputs. 51ohms and 47pF is a good starting point.

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  • If you can use the LTC1403-1, an easy solution is to use a fully differential amplifier like the ADA4945 between your filter circuit and the ADC input. Use the same +/-3V supplies for the ADA4945. Use figure 104 of the ADA4945 data sheet and connect VOCM to 1.5V and use 4.75k for RG and 1.96k for Rf. To minimize noise you may want to add an RC filter between the ADA4945 outputs and LTC1403-1 inputs. 51ohms and 47pF is a good starting point.

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