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Is it possible to use voltage attenuator AD8275 for driving 24 bit ADC ADS1220, without adding input Op-amp buffer?

I want to use AD8275 for attenuating the output from sensors varying from -10V to +10V, before giving to ADC.

Is AD8275 meant to use only for driving 16 bit successive approximation ADC? Is it possible to use AD8275 for driving 24-bit ADS1220, which is having sigma delta architecture?

Also, Can we use AD8275 without adding op-amp buffer at the input side? In which all system conditions, would you recommend to use input op-amp buffer?

  • There is no inherent reason that the AD8275 cannot be used to drive a 24-bit ADC, but the problem is that the noise and distortion (SINAD or THD + N) of the AD8275 is just 106 dB, corresponding to about 17 bits. If the AD8275 is not to degrade overall performance, the THD + N must be higher than the THD + N of the ADC. Since the theoretical best THD + N of an ADC occurs when there is no distortion and THD + N = SINAD, the theoretical best of which is 6.02 * n + 1.76 db, where”n” is the resolution of the ADC in bits, the highest resolution the AD8275 should be used for is less than 17 bits, and we come up with 16 bits. If you are willing to accept the fact that the AD8275 will degrade the system THD + N performance to about 16 to 17 bits, then you can use it to drive a 24-bit ADC. However, if you can tolerate that degradation, why use a 24-bit ADC? If the reason is because you have a 24-bit bus, then I suggest you use an ADC of resolution as low as your system really needs and set the lower bits to zero. That would provide a much more cost effective solution. On the other hand, if you are using a 24-bit ADC to get maximum linearity and the distortion is not an issue (as in the case where you are converting a d.c. voltage), then the THD may not be an issue and the noise can be averaged out with multiple conversions. On the other hand, if you really need 24-bit a.c. performance, they I suggest that the AD8275 is not what you need and you will probably have to design your own attenuator. For this, the amplifier you use will need an SNR of 146 dB or better.