ADS5407: Capacitive coupling or Transformer Coupling ?

Shyam Daram

Expert 1175 points

Part Number: ADS5407
Other Parts Discussed in Thread: LMH5401, ADC12J4000

Hi,

I have seen many development boards of ADC

Few have done Transformer coupling and few have done Capacitor coupling to achive proper AC coupling ?

My device of Interest is ADC5407 , my signal frequency is at 200MHz

I have gone through different articles where one major point people concluded is cost and noise involved in Transformer coupling

Experts may kindly through some light on which coupling is preferable for ADCs while targeting AC coupling

over 2 years ago

0 Rob Reeder over 2 years ago

TI__Mastermind 23810 points

Hi Shyam,

if your analog input frequency is 200MHz, then the ADC1-1WT+ will work for you as a transformer coupled to the ADC.

Regards,

Rob

0 Rob Reeder over 2 years ago in reply to Rob Reeder

TI__Mastermind 23810 points

Sorry, the PN: ADT1-1WT+ from Minicircuits

0 Shyam Daram over 2 years ago in reply to Rob Reeder

Expert 1175 points

Sir,

Thanks for the Suggestion, but my question is do i really i need transofrmer coupling, while high speed ADCs are coupled just with capacitor in the reference design of 2GHz Scope.

why do we need to go for tranformer coupling in my case.

0 Chase W over 2 years ago in reply to Shyam Daram

TI__Mastermind 19965 points

Shyam,

In our reference design for a 2GHz oscilloscope, we show both AC coupling and DC coupling with an active front end. The input is single ended and must be converted to differential for the ADC12J4000. On this reference design, this is performed using the LMH5401 FDA. The only AC coupling this design shows is in the very first switch of which you have the option to AC or DC couple the input by passing the tone through or around this 0.1uF capacitor.

Can you show us a basic schematic or diagram of how your analog front end would look using just caps? If the signal is already differential, then this should be possible. If the signal is single ended, you need either a balun or an amplifier to convert to differential input. I will await your response.

Thanks, Chase

0 Chase W over 2 years ago in reply to Chase W

TI__Mastermind 19965 points

Shyam, here is a video presentation of some analog front end considerations. It may be helpful to take a look at. https://training.ti.com/unraveling-practical-mysteries-behind-rf-converter-front-ends

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ADS5407: Capacitive coupling or Transformer Coupling ?