THS770012 and ADC16v130 interface

Gauraw,

I noticed that R13 is a 0ohm resistor shorting the signal path. Please verify that this is not placed.

Have you done a frequency sweep across the passband of your filter to verify it's passband frequency edges? If the filter is off, then the signal path will likely experience high attenuation.

Have you probed the output of the THS and verified that it outputs the desired amplitude? The series 50 ohm resistor and 100ohm termination at the ADC input results in AT LEAST 3.5dB of attenuation, more if you include filter loss. If you want 2.5V peak to peak at the ADC input, then you need AT LEAST 3.75 Vp-p at the THS output.

Regards, Josh 

Hi Josh,
R13,R19,R18,R20,R21 are not mounted on the PCB.I measured the voltages(peak-peak) at different points.The list is as following---

Voltage at R16 and R16 (THS side) 2.67Vpp..
Voltage at R16 and R16 (C57 side) 2.17Vpp..
Voltage at R7 and R6 1.22Vpp....
THS input at C86 and C87 833mVpp..

THS goes in saturation for more than this input.

Is there any other termination/load and filter configuration suggested?? THS datasheet P23 description says that 2.5Vpp at ADC input can be achieved, can you share that circuit??
Is it possible to get ADC16V130 simulation model?

Regards, Gauraw

Hi Josh,
Waiting for reply....

Gauraw

The ~5dB loss through the LC components of your filter may indicate:

1) The filter shape is not flat as you expect

2) The component Q is too low

You can minimize the filter loss by using high-Q components, and desiging for a small series R and large termination R

Here are some references/suggestions:

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=snoa569

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=snoa567

Here is an approximate model for the ADC. This represents the VIN+ input. The VIN- input will also look like this.

Regards, Josh

Hi Josh,
But can we go beyond 100ohms diff termination?? As ADC16V130 data sheet recommends max 10 ohms termination.

Hi Josh,
But can we go beyond 100ohms diff termination?? As ADC16V130 data sheet recommends max 100 ohms termination.(Correction)

Yes, you can go above 100ohms. Though the filter flatness may be more difficult to achieve and the ADCdynamic performance may not be as good.

Regards, Josh