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Can I use AC coupling capacitor on CWI/Q output of AD9279 ?

Question asked by shengwuei on Nov 11, 2014
Latest reply on Nov 11, 2014 by AshrafS

Hi Sir,

 

Below is the reference circuit of CW output circuitry of AD9279, the first stage(U401) is an I to V conversion stage and the second stage(U403) is a 20X voltage amplifier.

 

CW.png

According to the datasheet of AD9279, the CWI/Q outputs(CWI_POS/CWI_NEG on above schematic) are current output, with 1.5V DC level and +/-1.25mA full scale current.

 

Let's focus on the I to V stage, because DC level of CWI/Q output is 1.5V, and assuming the power supplies on ADA4841 is +/-5V, the maximum positive current output is limited to  (5-1.5)/3.9K = 0.8974mA, which is far from the maximum output current 1.25mA.

My question is, can I replace R455/R456 to a big capacitor(i.e. 22uF) to block the 1.5V DC, and connect positive inputs of ADA4841(U401.3 / U401.6) to ground, so the maximum positive current output is 5/3.9k = 1.2821mA ?

 

Thanks.

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