AD7653: input noise of AD7653

Question There is a unwanted noise coming out from the input pin as the figure shown. CH1(yellow): BUSY SIGNAL CH2(cyan): CNVST SIGNAL CH3(purple): UNWANTED SIGNAL FROM INPUT PIN Answer This is the natural behavior of the ADC input. On the CONVST falling edge (cyan), the ADC samples the signal at the input – you can see the glitch on the input coincident with the falling edge of CONVST. As per the operation of the AD7653 the ADC then hold with the cap switched in until the conversion is finished (as indicated by the Busy signal going low). At this point the conversion is complete and the ADC goes back into track, where the input again starts to charge the sampling cap to the correct level again. The time from when BUSY comes low until the next falling edge of the CNVST is then the acquisition time – it means that during this time the amplifier must settle the kick from the ADC and charge the ADC internal sampling cap to the correct and settled value before it is again sampled. Amplifier needs to be in the circuit – this enables the front end to settle correctly.

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AD7653 Production
The AD7653 is a 16-bit, 1 MSPS, charge redistribution SAR, analog-to-digital converter that operates from a single 5 V power supply. The part contains...
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AD7653 on Analog.com