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ADA4930 Input Common Mode Adjustment with Resistors

Question asked by Pete3 on Dec 19, 2012
Latest reply on Jan 14, 2013 by charlyelkhoury

I'm using the ADA4930 with a single 5V supply to convert from single ended to differential to drive an ADC. The circuit is connected to a 50ohm source and load and I'm trying to achieve a voltage gain of 14dB or higher. From Table 13 on pg 18 of the datasheet, 14dB should be possible but ideally I'd like 20dB. I need to set the Vocm to 0.95V for the ADC.

 

I need to increase the input common mode voltage using resistors as described on page 22 of the datasheet. I haven't been able to follow the procedure to get the results I want. I also haven't been able to replicate the example results.To example doesn't specify the Vocm being used but I found that 0.75V gave the correct values but then at Step 7 I get different values for B1 and B2.Has anyone been able to confirm the values in the example? Is it possible to use this procedure to calculate values that will give me a 14dB gain or higher?

 

Any help much appreciated,

 

Pete

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