Question on Sigma-Delta ADC

[Rainleo]

Hi, guys,
I am working on a receiver design. My sigma-delta ADC is running with a clock at 26MHz. Now I have a problem with the ADC output. There is always a tone located at around 13MHz. The tone is radiating into everywhere and destroy my noise figure at frf=n*13MHz. Anyone know what's happened?

 

[FvM]

If 26 MHz is the sampling clock, 13 MHz should be far out of signal band. It guess, you are observing normal operation with mid scale bias point.

 

[Rainleo]

Do you mean that delta-sigma ADC will always have a tone at around fclk/2 at its output? Thx.

 

[jiangxb]

the origin of the tone is various. they can be from pattern noise or mismatch of feedback dac components.