Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!mips!hal!mark From: mark@mips.COM (Mark G. Johnson) Newsgroups: sci.electronics Subject: Re: Impedance of a diode ? Message-ID: <45110@mips.mips.COM> Date: 22 Jan 91 15:57:26 GMT References: Sender: root@mips.COM Reply-To: mark@mips.COM (Mark G. Johnson) Distribution: sci Organization: MIPS Computer Systems, Inc. Lines: 21 In article jon_sree@world.std.com (Jon Sreekanth) writes: > >A rather curious query : what is the audio frequency impedance of >a reverse biased diode ? Off-hand, one would say, it's high, but >just how high ? > >Specifically, for a small signal diode like 1N4148, between 0 - 70 C, >with about 2.5 V or more of reverse bias, is the small signal audio >impedance at least > 1 Meg ? 10 Meg ? TI's datasheet (1966, revised 1973) for the 1N4148 sez that the max capacitance is 4 pF and the max leakage current at 100C is 3 microamperes (with 20V of reverse bias). Leakage current at room temp is 0.025 microamps. So a crude model would be a 6.7Megohm resistor in parallel with a 4pF capacitor. At 20kHz, 4pF has a capacitive reactance of 2 Megohms. -- -- Mark Johnson MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086 (408) 524-8308 mark@mips.com {or ...!decwrl!mips!mark}