I’ve been monitoring all your comments and investigating your data concerning the Quad bandwidth topic.
I ordered a Quad, but not received it yet.
I have the schematic, component datasheets, and have been using Slimfish’s “Quad.zip” file for analysys. Thanks Slimfish, you saved me the trouble.
This is my $.02
In my mind, the first logical step is the 72Ms/s sample rate issue.
I like lygra’s take on this and the sampling chart.
I personally would want an accurate graphical representation of a signal, otherwise, want’s the point?
My Instek GDS-1062A has a sample rate of 1Gs/s and 60MHz bandwidth.
With a 60MHz signal, that works out to 16 samples per cycle, and that many samples per cycle on the Quad would be for a 4.5MHz signal.
I don’t see the Quad being useful beyond 10MHz.
Now for the OPA2354 opamp issue.
With all range switches open, the amp has a gain of 10, the datasheet shows a small signal bandwidth f-3db = 10MHz at a gain of 10.
Also I noticed the power supplies are 3.6 and -3.0 which exceed the max specified voltage of 5.5V, but not the absolute max rating of 7.5V.
I’m wondering if this will effect the slew rates/bandwidth because operating a transistor close to breakdown voltage increases leakage current possibly causing slower response.
As far as testing an actual Quad, I have a scope and a Parallax Propeller proto-board, there is a demo for synthesizing square waves up to 120MHz
Tina-TI testing confirms a lot of what everyone has been saying.
I plan to modify Slimfish’s circuit to include a scope probe and function generator impedence.
I’m aware that spice programs don’t include parasitic signals and stray capacitance, Spice is for before/after picture, looking for improvement. The designer should know the limits of spice and compensate for it in the real world.
I’ll post more when I have more, Thanks