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ADS5282EVM DC coupling & alternatives parts more suitable for dc coupling

sujeeva wettasinghe
Intellectual 460 points
Other Parts Discussed in Thread: ADS5282EVM, ADS5282

 

My customer  is working on an investigation that requires simultaneous digitisation of at least 6 signals at a rate of at least 50 MSPS. Since it is a preliminary investigation, I prefer to use an evaluation board rather than design a custom PCB. Using single ended.

 

I have been using an ADS5282EVM (8-channel, 50 MSPS), but it has proven unsuitable as the application requires DC-coupling the ADC inputs.

 

  1. Is there an alternative ADC evaluation board that provides DC-coupled inputs along with the other requirements mentioned above?

  1. Does TI have any recommendations for DC-coupling the ADS5282 and/or modifying the ADS5282EVM to achieve this?

Sujeeva Wettasinghe

Avnet FAE

 

  • 0
    TI__Mastermind 29220 points

    Hi,

    No, there is not an EVM for this device that has DC coupled inputs by default.

    Our EVMs almost always come with transformer coupled inputs by default, and usually there are options available on the board for it to be modified for DC coupling.  The reason we start with transformer coupling is that it is really the only way to evaluate the performance of the ADC by itself and not the performance of the ADC plus the performance of the signal conditioning circuitry.  All our modern high speed ADCs require a fully differential input signal of a certain max amplitude and biased up to a certain input voltage level.  It is rarely the case that the customer's input signal happens to be fully differential with 2V peak to peak and centered around 1.5V, so there has to be some input signal conditioning.  And the signal generators available that have good enough performance to let the EVM approach datasheet performance specs are all single ended.  So there needs to be some single ended to differential conversion and some biasing up to the VCM voltage.  This can be done with a differential amplifier or with transformer coupling.  The amplifier injects its own AC performance limitations into the evaluation while the transformer coupling lets us more nearly show what the ADC itself is capable of.

    On the ADS5282 EVM that you ask about, each channel has an SMA input for a single ended input to the transformer, with the other side of the transformer input grounded through a zero ohm resistor.  You can see an optional second SMA input where the SMA in not installed by default.  Each channel could have the second SMA soldered in, the zero ohm resistor to ground removed, and the transformer removed.  Then a couple of zero ohm resistors could be soldered down to the transformer pads to short the primary side to the secondary side.  With that, the channel is DC coupled straight from the SMA inputs to the ADC.   At that point the customer would need to do their own signal conditioning to get their signal to a 2V peak to peak fully diferential signal biased around 1.5V and couple that signal into the ADC EVM.  If they choose an appropriate amplifier to do the signal conditioning, then they could set up the amplifier EVM appropriately and then couple that to the ADC EVM.

    Regards,

    Richard P.