Would this be practical across the usual 1 Hz to 1 MHz or so range of a function gen? Wouldn't you have to switch the integration capacitor/resistor?
yes, so ? rotary switch to switch a resistor bank around. nothing wrong with that. they have been doing this for year ( or reed relays to switch them around )
Do you have an example of a general-purpose function generator (square/triangle/sine, 1 Hz to 1 MHz, < 1V to 20V amplitude, DC offset, usually symmetry/duty cycle adjustment) that used this principle ?
the older hp's like the 332x series (3324 / 3325) did that. i believe also the 8116, although that one may have used a sine shaper. Bk precision did it ( sold as tektronix generators)
Many of these (eg. AD9834) provide sine, square and triangular waves. Somewhat similar to the MAX038. Add an output stage for amplitude and DC offset control, a micro and some controls and you essentially have a function generator. Many of the cheap ones do this.
the problem is this filter, gainstage and output stage ... also the dc offset control is problematic. but you still can't sweep, have no slope control or anything. most of these designs come no further than the micro and AD9834 chip.. that's easy. its just digital and software... the problems start when they have to cross in the analog domain...
The price goes up very quickly at this point.
If you want to get an idea of what is involved : download the service manuals of something like an Agilent 33120 or 33250 and take a look at the filter , dc offset and output driver stage... it is -VERY- complex.. None of those fleabay generators will dare tread in that area...
As for value : you can pick up a used hp 3325 sometimes as low as 100US $ on ebay. DDS and al... 0 .. 60 MHz 40vPP with sweeping / modulation and plenty of other stuff. It even has a marker output. Ideal to use if you want to do bode plots. Hook up generator output to scope channel 1 and input of system under test. Output of system under test goes to scope channel 2. marker output goes to scope channel 3. Set scope to substract cannhel 2 from 1. and show trace 3 + math trace. the marker output is a signal that goes low when the sweep begins and goes from low to high when a preset frequency is set. so you create a 'cursor' this way. you can program this marker frequency. so now you can read gain versus frequency. the generator tells you exactly where you are looking in the sweep. Such machines are incredibly useful. If you trust the output to be constant you can get away with a dual channel scope simply look at the output of the system under test and the marker. put scope to external trigger and let the geenrator trigger the scope when the sweep starts.
I bought mine for 150... with all options installed (3325B). it'll run circles around those fleabay things.
And this 'driving microcontrollers with it ? why would you want to do that ? slap a crystal on them and off you go. Besides most micros run at 16MHz or faster these days ...
Anyway, i would not buy a scope with signal generator in it. Invest a bit more and buy a better scope. the times you need a signal generator are very limited ...