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Switching signals and input conditioning for 1GHz data acquisition

flix
Prodigy 40 points
Other Parts Discussed in Thread: ADS5474, THS4304, THS9000, THS4509

Hi,

I am dreaming of a system with 2-4 ADS5474 (14bit-400MHz) to measure decay times.

To be more flexible, I would like to offer the possibility to either sample 1 channel with (if possible) 1.6 GHz (=400MHz *4), or 4 channels with 400MHz.

Do you think, that signal switching with a RF relais, e. g. a Meder CRF 7GHz Reed relais, makes sense? I also looked for semiconductor switches, but the 1GHz semiconductor switches as e. g. the ts3usb211e specify a propagation delay jitter of 0.2ns, which is far too much.

Further question: The ADS5474 EVM boards usually use a fully passive input handling with transformers. To be more flexible and to facilitate input protection, I would prefer to use a high-speed OP, as e. g. the THS4304. Does this make sense (are there application boards with OP input conditioning available anywhere?) or is this a more stupid idea?

  • 0
    TI__Mastermind 18095 points

    Using switching relays may be possible but we have never implemented this approach.

    It is possible to use a high speed op-amp input interface tot he ADC.  The THS4509 op-amp is recommended for those applications.  Note, the addition of active circuitry will typcially degrade SNR performance (due to noise output of op-amp) and degrade SFDR performance (due to harmonics from the op-amp).  Many of the TI ADC EVMs provide an option for the THS4509 interface.  The ADS5474 does have an option to use two THS9000 IF amplifiers (one for each differential leg).  Alternatively, a separate TI THS4509 could be used and connected differentially to the ADC with the transformers bypassed for evaluation purposes.

    --RJH