Digital capacitance devices

Does anyone know of a device that allows digital capcitance or is this just not possible?

The range of capacitiance should be about 60 to 160, this is to be used in a radio reciever for FM (88mhz-108mhz), but doesn't have to be that capacitance range

anyone heard of such a device or have any ideas??

pike said:

Does anyone know of a device that allows digital capcitance or is this just not possible?

The range of capacitiance should be about 60 to 160, this is to be used in a radio reciever for FM (88mhz-108mhz), but doesn't have to be that capacitance range

anyone heard of such a device or have any ideas??

Click to expand...

FM radios usually use varactor diodes for tuning, for digital tuning they are usually part of a PLL circuit (in the VCO) - although for analogue tuning they are just fed from a pot.

To do it 'digitally' you could use a D2A to produce a DC voltage from a digital signal, simple PWM techniques are commonly used in TV's and radios.

Your capacitance range looks far too high for VHF tuning, something like 25pF tuning capacitors are usually used for the VHF band. Try doing the maths to find the capacitance change required.

I never though of that (i never heard of it either), but that is a brilliant idea to whoever discovered a capacitance on a "reverse-biased diode junction"

Thanks alot nigel!!

pike said:

I never though of that (i never heard of it either), but that is a brilliant idea to whoever discovered a capacitance on a "reverse-biased diode junction"

Click to expand...

A reverse biased 1A rectifier makes quite a good varactor diode, it's a lot cheaper, and you probably already have them!.