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ADS5263 VCM input voltage range and ADS5263 spice model

Question asked by antonf on May 11, 2018
Latest reply on May 11, 2018 by JinoL

Hello!

I'm trying to simulate ADC driver based on AD8139. It is supposed to drive ADS5263

Please see ltspice schematics attached to the post. Supply rails are 0v and 10v. ADC requires Vocm=1.5V, so V=1.5V is supplied to VCM pin of AD8139. Amplifier's gain is set to G=1. V=3.75V is supplied to inverting input of amplifier circuit, while signal with swing of 1.75..5.84V goes to non inverting input of the circuit.

Expected output swing at diffamp positive pin is:  0.5V .. 2.54V. I believe both input and output voltage swings are within values recommended by  AD8139's datasheet. In particular AD8139's datasheet says VCM voltage swing −3.8..+3.8 for supply voltage +-5V. One can also see similar data on Figure 51 of the datasheet. So for my Vee=0V Vcc=10V allowed VCM voltage swing should be +1.2..+8.8V. Am I right? However the simulation shows Vocm=(Vpos+Vneg)/2=~1.67V which is far from 1.5V.

So is the model incorrect or VCM=1.5V is too low for AD8139?

 

I would also like to note that noise model of AD8139 is still incorrect (as has been already mentioned in AD8139 noise response ). Is there updated model as Tina promised?

 

Thank you!

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