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Entry  Wed May 13 09:31:18 2015, Chenfei Yang, transparent-mode voltage tek00000_.png
    Reply  Wed May 13 09:45:51 2015, Stefan Ritt, transparent-mode voltage 
       Reply  Wed May 13 09:55:09 2015, Chenfei Yang, transparent-mode voltage 
          Reply  Wed May 13 10:16:40 2015, Stefan Ritt, transparent-mode voltage 
             Reply  Wed May 13 10:27:43 2015, Chenfei Yang, transparent-mode voltage 
             Reply  Wed May 13 12:34:49 2015, Stefan Ritt, transparent-mode voltage 
                Reply  Wed May 13 12:52:22 2015, Chenfei Yang, transparent-mode voltage 
                Reply  Wed May 13 16:13:07 2015, Chenfei Yang, transparent-mode voltage 
                   Reply  Wed May 13 16:25:24 2015, Stefan Ritt, transparent-mode voltage 
Message ID: 415     Entry time: Wed May 13 10:16:40 2015     In reply to: 414     Reply to this: 416   417
Author: Stefan Ritt 
Subject: transparent-mode voltage 

I see your point. Actually I will soon have the same issue since we design right now a board with an AD9637 using the transparent mode. Which one are you using? The common mode range given in the datasheet is limited to guarantee optimal performance. But some ADCs allow a slightly bigger common mode range with reduced performance, but which might still be ok for some application. A "real" solution would be to put switchable level shifters between the DRS and the ADC, but that requires 8 additional chips which is bad. Alternative the ADC could pick up the signal not at the DRS output but at the DRS input, but that would aslo require additional chips for multiplexing. So unfortunately no perfect solution for that...

Chenfei Yang wrote:

Here's the problem. My external ADC has 2Vpp differtial input voltage range. And the common-mode voltage of the inputs need to be 1.3V. I cannot make both the transparent-output and the readout-output meet the ADC input requirement.

Stefan Ritt wrote:

The ROFS signal has no effect in the transparent mode, so you have to adjust O_OFS between sampling and transparent mode accordingly. Either use a DAC or two voltages with an analog switch.

Chenfei Yang wrote:

Hello Mr. Stefan Ritt

  For DRS4 differential inputs ranges form 500mV to 1100mV, with ROFS set to 1.55V, O_OFS set to 1.3V, the outputs of DRS4 is shown in the attachment.

  The left part of the waveform,DRS4 works in transparent mode, and then the readout take place. The DMV of transparent mode is bigger then the readout mode, and that makes ADC sampling harder.How may I solve this problem?

  Best wishes!

                                 Chenfei Yang

 

 

 

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