Question
We are currently testing the Analog Devices ultrafast ADCMP573 in order to useit for high frequency (The comparator does not work as expected.
The output signal switches 5 ns after the 5 MHzinput signal Vp exceeds the reference voltage Vn,instead of the 150 ps propagation delay announced in the component datasheet.
The output rise and fall times were also measured; they fluctuate around 400 psinstead of the expected 35 ps.
Answer
The slew rate of the input might be causingthe rise time and propagation delay to increase.Approximating the slew rate of the input would be equal to around 500mV/20ns or0.025V/ns. This is very low compared to the test conditions on ourspecification table.
The propagation delay increases as the slew rate on the input decreases asshown in figure 18 on the data sheet.
I suggest using a signal generator at the input where you can have a fasterslew rate compared to the current setup.