ADS5401 / Input capacitance and equivalent circuit and of CLKIN

Hi,

I have asked the design manager for an equivalent input circuit for the clock input of the device.   We sometimes have such an equivalent circuit listed in the datasheet but for this device we did not.   I suspect that internal loading on the clock input may be making it harder to drive a larger input swing at the higher sample rates, although I haven't seen it on my EVM, perhaps due to my using a 50 ohm signal source that is able to drive the signal.   If capacitive loading on the signal is an issue, what I have seen done on other devices is to use an L-C matching circuit external to the clock input.  An example of this is described in the application note http://www.ti.com/lit/an/slyt679/slyt679.pdf .    But in order to try this same approach with the ADS5401 we would need to have the s parameters of the clock input or at least an equivalent circuit of the clock input, so I have asked for this.

Regards,

Richard P.

Hi Richard-san,

I would like to confirm additionally.

You said that " I haven't seen it on my EVM".

Is this the condition using the LMK04131?

Please let me know if there is lack of information.

Regards,

Kuramochi

Kuramochi,

I am covering for Richard while he is on vacation. I looked at the ADS5401EVM and the clock input is coming from an external signal generator through a transformer. There is no LMK04131 in the path.

Regards,

Jim   

Jim-san,

Thank you for your answer.

Is it difficult  to get the input capacitance and/or equivalent circuit and of CLKIN?

Best Regards,

Kuramochi

Kuramochi-san,

I have requested the input capacitance information from the design team. The equivalent circuit is shown below.

Regards,

Jim

Kuramochi-san,

It was just Figure 36 from the data sheet.

Regards,

Jim