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What's against using real capacitors? Foil and film capacitors can have good long term stability and low temperature coefficient, you probably need calibration to get rid of the initial tolerance.
1-2uf is fine, I looked into whats called a capacitance multiplier incorporated with oamps and I would not have made this topic had the circuit been absent of capacitors, how ever it would work if the capacitor it uses can be really small since small caps can be made quite precise. I made this topic because I am looking for anything but that circuit.
I don't understand???
You want the tolerance to be within 1%, but you don't really care about the value on what you
actually want.
You also didn't specify what type of capacitor you desire. i.e. Electrolytic, MKT, Ceramic etc.
Also, what voltage rating?
You can obtain Silver Mica types which are 1% rated@500V, but their values don't go higher
than 1000pF (1nF or 0.001uF).
The Silver Mica types are mainly used for valve radio restoration and are expensive.
Please see link:
There is an op-amp ckt that can act as a large fixed cap for signal levels - using a high precision cap (smaller) as a reference should allow you to synthesize what you are seeking ...
Okay, so get a 1.5uF 20% capacitor. Measure it's value with a precision of 1%. Say it measures 1.62uF. You now have a 1.62uF capacitor with a tolerance 1%, which satisfies your requirement.
Okay, so get a 1.5uF 20% capacitor. Measure it's value with a precision of 1%. Say it measures 1.62uF. You now have a 1.62uF capacitor with a tolerance 1%, which satisfies your requirement.
Besides temperature, humidity is a relevant drift factor. If you study manufacturers application notes, you'll find that among standard capacitor dielectrics, polypropylene gives best overall drift performance. 1% seems feasible.
Besides temperature, humidity is a relevant drift factor. If you study manufacturers application notes, you'll find that among standard capacitor dielectrics, polypropylene gives best overall drift performance. 1% seems feasible.
@fvm - So the short answer is that the tolerance gives you and idea of its stability under various conditions e.g. Voltage , frequency , temp , humidity??? And you need to go to the datasheet to get and idea how it will perform in your particular application. Or is the manufacturer saying we really don't know what the value will be when we make it. But we guarantee it will be within this tolerance range.
Tolerance is some kind of overview ....
* you may have a 5% tolerated capacitor with high accuracy, but bad temperature drift
* but the capacitor may also have large fluctuations because of production... while it has low temperature drift.
The manufacturer is making the capacitors with a tolerance specification and doesn't guarantee anything beyond it. A brief check of distributor selection guides tells you that e.g. 1µF 1% polypropylene capacitors are listed but not stocked. You can expect that similar types with 5 or 10% tolerance have similar drift parameters. As discussed by bobTPH, they can be used for precision purposes after determining the exact capacitance.
Tolerance and stability are two different things. Here is an example. This is a 1uF C0G MLCC that is listed at 10% tolerance, but has a 30 ppm temperature coefficient and 0% / decade aging coefficient. In other words, once you determine it's exact value it will hold that well within 1% over a large range of temperatures and over time. A bit pricey though, I must admit.
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