Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!lll-winken!uunet!zephyr.ens.tek.com!gvgpsa!gold.gvg.tek.com!grege From: grege@gold.gvg.tek.com (Greg Ebert) Newsgroups: sci.electronics Subject: Re: Impedance of a diode ? Message-ID: <1902@gold.gvg.tek.com> Date: 22 Jan 91 21:24:35 GMT References: Distribution: sci Organization: Grass Valley Group, Grass Valley, CA Lines: 18 A reverse-biased diode will have an appreciable impedance at audio frequencies, because the main mechanism is junction capacitance, which decreases as more reverse-bias is applied. You can measure it by connecting a DC source, audio generator, diode, and a variable resistor, all in series. Set the audio generator to, say, 0.1v p-p, and adjust the resistor until the voltage across the resistor is 0.05v p-p. Measure the resistance; it equals the diode's impedance *at the measured frequency*. Try varying the frequency. I've never measured the impedance of diodes before, but I would expect it to be near a megohm at 1Khz. Now forward-bias the diode and repeat the experiment. Neat eh ? Diodes make nifty (but sometimes noisy) analog switches. ----> NOTE ! Use a scope with a 10X probe to reduce loading effects. You should parallel the variable resistor with the scope (1M or 10M) when you measure it. Otherwise, you'll have to do some calculations (not hard).