Hello,
We would like to use AD9690 & AD9697 in oscilloscope front end. With an oscilloscope you are often looking at a small portion of a large waveform and so the signal will be over range for a significant part of the time and must recover quickly when the signal comes back into range. So I have 2 questions;
1. What is the maximum input range for the ADC which will prevent long term damage and also ensure quick recovery?
2. What is the recovery time from overload to <1 LSB?
1. On max input range we have:
AD9690 data sheet, rev B, page 11 Table 6 ABSOLUTE MAXIMUM RATINGS: VIN± to AGND = 3.2V. Also page 28:
"The absolute maximum input swing allowed at the inputs of the
AD9690 is 4.3 V p-p differential. Signals operating near or at
this level can cause permanent damage to the ADC"
- That would be 2.05Vcm+/-(4.3/4)V= 0.975-3.125V.
AD9697 data sheet, rev 0, page 11 Table 6 ABSOLUTE MAXIMUM RATINGS: VIN± to AGND − 0.3 V to AVDD3 + 0.3 V = -0.3 to +2.8V. Also page 23:
"The absolute maximum input swing allowed at the inputs of the
AD9697 is 5.6 V p-p differential. Signals operating near or at
this level can cause permanent damage to the ADC"
- That would be 1.41Vcm+/-(5.6/4)=0.01-2.81V.
So a few issues here:
The AD9697 seems clear that max input range is 0-2.8V from both table 6 and page 23. But for the AD9690 the range is limited to 0.975-3.125V. A smaller range for the device that has a higher AVDD3 (3.3V vs 2.5V)? Is it because the AD9690 input can be 50-400ohm? Whereas the AD9697 is fixed at 200ohm. And if so, what is the AD9690 limit when set to 200ohm?
Second, "Signals operating near or at this level can cause permanent damage". That is a bit ambiguous. What is the safe long term range than can be used?
2. Overload recovery time.
I could not find any spec in the data sheet for overload recovery time on the analog input. It is normally spec'd as time to settle to 0.1%, but would also be good to know time to settle to 1 LSB if that is possible.
Thanks for any help!
Best regards, Ken
