THS3217: Linearity Issue

Andrew Baek

Intellectual 905 points

Part Number: THS3217
Other Parts Discussed in Thread: DAC39J82,

Hello,

Our design includes DAC39J82 and THS3217.

The THS3217 circuits closely follows one of the DAC eval boards.

However, we are observing significant distortions.

Attached are

copy of the schematic related to the DAC39J82 and THS3217
Powerpoint to describe the distortions

We have tried to reduce the gain but still distortions are severe.

Also the external filter shows a tilt across the frequency range, which was expected to be flat.

Regards,

Andrew

AWG_1V07 ths3217.pdf

over 5 years ago

0 Andrew Baek over 5 years ago

Intellectual 905 points

ths3217.pptx

0 Micah B Brouwer over 5 years ago in reply to Andrew Baek

TI__Intellectual 1910 points

Hi Andrew,

Thanks for reaching out, we are reviewing your schematic. What you are expecting to see on the input and output of the THS3217? Some insight into the expected performance would be helpful.

0 Micah B Brouwer over 5 years ago in reply to Micah B Brouwer

TI__Intellectual 1910 points

Hi Andrew,

It appears the interstage filter is heavily loading the output stage and causing an oscillation. I simulated your circuit with TINA, see the circuit and results below:

When the filter is removed and VINP is directly connected to VO1, the peaking in the frequency response goes away. To further confirm this, a 50 ohm isolation resistor was added in series between VO1 and the interstage filter, and that also removed the peaking. Of course, doing this also affects the filter's response.

Could you please verify that this is the problem by removing the interstage filter and seeing if the distortion disappears?

THS3217.TSC

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THS3217: Linearity Issue