wyyll
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Posts: 4
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Hi Venkats,
Given the age of this thread, I am hopeful that you have solved your problems, and can post here what the solution is so we can all learn from it.
In the event not, I have a few points to add.
The noise looks like digital clock noise coupling into your output, perhaps through the digital wires driving the current-steering differential pairs in your DAC as was suggested. In the small chance you haven't already done this, did you double buffer the digital control inputs onto your local supplies? Otherwise you inject the noise in your driving ADC into your own DAC. I would also look for your local clock coupling onto the bias voltage which sets up the currents which are steered. I would also look for the ESD diodes in your pad schematic to be injecting power supply noise, but this should be common-mode assuming the ESD diode areas are identical. I mention this last bit because you said adding power supply bypass capacitance reduced the magnitude of the problem
As for the glitches (pink waveform) on falling edges, but not rising, is this a single-ended output, or differential? The signal label IOP suggests it might be single ended, with the other output IOM not shown, or non-exsistent. For this case, I expect that the cause of the glitch is the charge-injection associated with turning your current steering switches on and off. For a falling edge, discharging the steering transistor creates a charge flow opposite to the intended for a short amount of time. For a rising edge, this charge flow would be of the opposite direction, and might not be visible in your waveform. This typically occurs if you size your current-steering differential pair too large to get the series resistance down, or the current you are steering is too small. I am not surprised that this shows up only when you add in the series inductance of the bond wires.
I hope you find this helpful.
Will.
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