Timeline for How do I get output impedence of ICs?
Current License: CC BY-SA 3.0
14 events
| when toggle format | what | by | license | comment | |
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| May 19, 2016 at 20:35 | comment | added | KalleMP | Spend an afternoon characterising the impedance of a few different ICs. Learn a bunch I expect, I would. I think in the 10 to 1000 Ohm depending on technology and IC application. Also many technologies (and function pins) have unequal push and pull impedances. | |
| May 19, 2016 at 17:18 | vote | accept | Sreeraj Chundayil | ||
| May 19, 2016 at 16:04 | comment | added | Transistor | @InQusitive: If you add a schematic of the circuit you are teaching you will get a better response. I suspect you are confusing passive RC filters with active which have output impedance of only a few ohms. | |
| May 19, 2016 at 15:40 | answer | added | Spehro 'speff' Pefhany | timeline score: 3 | |
| May 19, 2016 at 15:27 | answer | added | dim | timeline score: 1 | |
| May 19, 2016 at 15:05 | comment | added | pjc50 | You could actually work out the output impedance by constructing a couple of filters and measuring their properties - there will be a small error which you can work back in the equations to give the impedance. | |
| May 19, 2016 at 14:28 | comment | added | JIm Dearden | The output circuit of a 555 is a complimentary pair quite capable of driving currents (source and sink) up to 200mA, so for all practical purposes just ignore the output impedance - just make sure you use reasonable size resistors for the filter (> 1k0) | |
| May 19, 2016 at 14:17 | comment | added | Ignacio Vazquez-Abrams | Output impedance is, as always, voltage drop/lift divided by current. | |
| May 19, 2016 at 14:13 | comment | added | Scott Seidman | There is no such thing as "exact". There is a specification of how close you need to be. Think about what the error will be if, for example, your filter is designed with a 10K input impedance at DC, and you have a source with an output impedance of 4 ohms as opposed to 0 ohms. | |
| May 19, 2016 at 14:11 | comment | added | Andy aka | An op-amp's output impedance (as a unity gain buffer) is going to be an ohm or so at audio so, add the 1 ohm to the filter resistance of (say) 1 kohm and you get a 0.1% error. At 1 MHz the op-amp has to be chosen carefully but less than 10 ohms is definitely realistic. | |
| May 19, 2016 at 14:09 | comment | added | Sreeraj Chundayil | @ScottSeidman: But to get the cutoff frequency don't I need the exact resistance value? | |
| May 19, 2016 at 14:07 | comment | added | Andy aka | Surely it's best to use sinewaves to demonstrate filters and the 555 produces a square wave (rich in harmonics). | |
| May 19, 2016 at 14:05 | comment | added | Scott Seidman | put an op amp follower on your output stage, and then the output impedance is a few ohms and you don't need to worry about it. | |
| May 19, 2016 at 14:03 | history | asked | Sreeraj Chundayil | CC BY-SA 3.0 |