I just started thinking about building a function generator with MAX038.
The Output Frequency is calculated as followd: F0 = IIN(uA) / Cosc (pF).
IIn should range from 2uA to 750uA. That's not the problem.
But to get a Frequency Range from say: 1Hz to 20MHz the Capacitor as to change. So my question is: Is it possible to switch the Capacitor at the COSC Pin with an anlog switch or multiplexer (like MAX310)? Isn't the Ron of the switch a problem? How could i manage to control the full frequency range digital? Is there anything like a "digital adjustable capacitor" like there are digital potentiometers?
I don't understand how Maxim did a Frequency Range from 1kHz to 16MHz in 1kHz steps with a single 35pF Capacitor?
MAX038 Datasheet: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257
Application Note: http://www.maxim-ic.com/appnotes.cfm/appnote_number/650