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REFT & REFB & Input Span problems with AD9235

Question asked by Chuck on Dec 22, 2011
Latest reply on Jan 21, 2012 by PMH

Im using AD9235-20 in single-ended configuration with 1V applied to Vin-.The power supply of AVDD and DRVDD were both 3.3V.And the clk was drived by a 10.000Mhz-crystal-controlled oscillator.

 

The testing source came from a regulated power supply.The problem was that,when input varied from 0v to 2v,AD9235 could only accept signals ranged from 0V-1.9V(When   Vin+ was applied with a level above 1.9V,the OTR changed to ’1‘).

 

So I used a multimeter to check several pins.Sense&Mode pins were connected to ground.To my surprise,the voltages at REFT & REFB pins were 2.29V and 1.28V respectively.They should be 2.15V and 1.15V.

 

Was it wrong to using a multimeter to check the REFT & REFB pins?(Maybe the output impedance at REFT & REFB pins cannot be ignored compared to a multimeter.)

 

Or the power supply were too high?(I tried a 3V power supply.And the voltage at REFT & REFB pins changed to 2.1V and 1.1V respectively.)

Or the input impedance didn't match because i only applied the 1V of CM to Vin-?( I have noticed the Fig37 in datasheet of AD9235.But if i had used  AD9235 in that way,I couldn't have got the DC component in my signal.)

 

Can anyone help me,plz?

If needed,i can upload the picture of my schematic diagram of AD9235.

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