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i have ADS1672Datasheet from TI. in it's datasheet circuit that is recommended for differential interface is: Basic Analog signal connection

but i want to remove amplifier(THS4520 datasheet-it's a Fully differential amplifier) and connect analog input directly to my ADC(ADS1672) ,to simplify circuits.

but i don't know what will happen if i remove it. thanks all.

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  • \$\begingroup\$ Check the ADC input impedance. It might be rather low if they recommend an amplifier. \$\endgroup\$
    – Oldfart
    Jun 6 '18 at 22:01
  • \$\begingroup\$ What are you connecting to the ADC? Input impedance on your ADC is pretty low (figure 22 on page 14 of the datasheet you linked). This means it will load down whatever you are connecting...may be no problem, may be a big problem. \$\endgroup\$ Jun 6 '18 at 22:07
  • \$\begingroup\$ @Oldfart i'm in testing and setting up this ADC. and in fact i connect an potentiometer to input... but the values that i'm reading is very away of thing that have to be... such as sign(it's two's complement output) is that because of eliminating THS4520?? \$\endgroup\$ Jun 6 '18 at 22:39
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The data sheet tells you that the sum of AINN and AINP must typically add to 5 volts. This means the average is 2.5 volts. That is what the common-mode voltage on the VCM pin is all about and that is why the differential amplifiers use the voltage on VCM to set there differential outputs to be nominally biased at 2.5 volts. So, typical acceptable values for AINN and AINP are: -

  • 2.5 volts and 2.5 volts
  • 1.5 volts and 3.5 volts
  • 3.5 volts and 1.5 volts

what will happen if i don't use amplifier before my differential ADC

If you don't stick to the sort of values as shown above then all bets are off because the data sheet doesn't tell you and nobody can guess.

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The amplifier before the ADC is for proper electric conditioning of the signal such that voltage/impedance would fit the ADC range. This amplifier is not a must once your signal is already appropriated to the ADC’s specification.

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