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What op amp to use as buffer in ultrasound application

Question asked by analog.interest on Sep 30, 2015
Latest reply on Oct 15, 2015 by analog.interest

We are working on a 40 MHz board for an ultrasound application, and on the receive side, we are planning to use an ultrasound-specific LNA (https://datasheets.maximintegrated.com/en/ds/MAX2034.pdf) that has differential output and a Vcm of 2.5 V.

 

I am looking for an op amp to buffer the signal from the LNA off-board, and came across the AD8044 (http://www.analog.com/media/en/technical-documentation/data-sheets/AD8044.pdf). If we could use this with G = +1 V/V or +2 V/V, I think that would be ideal for our application.

 

However, I am having difficulties understanding (1) whether this op amp is actually what we are looking for in terms of compatibility and (2) if it is what we are looking for, how to connect it.

 

If we connect the positive/negative output of the LNA to the positive/negative input of the AD8044, how do we connect the feedback to set the gain? I think we would use something similar to what is described here (www.electronics-tutorials.ws/opamp/opamp_5.html) with R1 = R2 = R3 = R4, but there are probably more trade-offs that I am not yet aware of.

 

Page 11 of the LNA datasheet has 100 nF cas at the output to filter out the DC component of the signal, but if we use the AD8044 with the single +5 V supply, we would leave these caps out and the input voltage for the AD8044 would be correctly biased (around 2.5 V). We could then put the 100 nF caps at the output of the buffer to DC filter the signal. Does this look correct?

 

Thank you for taking the time to read and consider these questions.

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