Question about the square-wave output with LTC1668

A square-wave of 92kHz will be created with LTC1668. the circuit is shown below.

Its CLK pin and I/O pins are connected with a FPGA chip.  Its clock is 20MHz. The input to I/O is switched between oxFFFF and ox0000 with  92kHz..

The signal between A (or B) and AGND meet expectation,  such as

BUT, the signal bwteen A and B (differential output) DON'T like a square-wave, just like

What is the  reason? How to get a good square wave?

Top Replies