ADS6142: Resister values on the analog inputs

Hi,

In that application circuit the two 200 ohm resistors are the load for the amplifier driver circuit.  In this case the example circuit was designed for a 400 ohm load, following a simple RC filter with components labeled as Rfil and Cfil.  Amplifiers such as this usually don't do well driving a heavy load like a 50 ohm load and will usually be designed for something like a 200 ohm to 400 ohm load.  So using a value a little larger or smaller than 200 ohms is fine.  For specific questions about the behavior of the amp into different loads, the amplifier forum would be the best place for that.

The series 5 ohm resistors right in front of the ADC are there to attenuate some of the sampling glitch energy that radiates out from the ADC input when the sample clock switches.  There will be some voltage drop of the input signal across the 5 ohm resistors so that should be accounted for as the gain of the drive stage is designed, if you want to drive the signal to full scale.   This ADC does not have an isolation buffer on the ADC front end inside the device, so when the sample clock switches there will be some glitch energy come from the ADC onto the analog input signal, and those 5 ohm resistors will block some of that.  Again, these resistors could be 4.7ohm or 5.6 ohm, or they could even be 10 ohm - keeping in mind that a little of your input signal will be dropped across the resistor.

Regards,

Richard P.

Ken-san,

Looking forward to receive the answers sohrtly.

Mita