Colpitts Oscillator Calculator

Colpitts oscillator

Colpitts oscillator formula

Enter the Frequency Desired


A colpitts oscillator is an oscillator circuit that uses an inductor and 2 capacitors in order to create a resonant frequency. It it s a type of LC oscillator.

A colpitts oscillator uses a single inductor across 2 capacitors that are in series.

Colpitts oscillators can be built with transistors, op amps, or logic chips such as inverter chips. If amplification is desired, then you would need to use an active device such as an op amp or transistor.

In this circuit, we calculate a colpitts oscillator frequency based on the formula, frequency= 1/2π√ LCt, where L is the value of the inductor and CT is the equivalent capacitance of the capacitors in series. The equivalent capacitance in series is equal to the product of the capacitors divided by the sum of the capacitors. This gives the equivalent capacitance in series.

This calculator uses a variety of inductor and capacitor values. This calculator tries to take into account that for breadboarding purposes, large inductor values are usually very hard to find. Components easily obtained for inductors are values from 0.1μH to 4700μH. Therefore, this calculator only uses large inductor values (in the henries) for very small frequencies such as from 1Hz to 100Hz. Other than this, large inductor values are avoided due to the fact of not easy accessibility.

Capacitor values may range from picofarads to millifarads. Just like with inductors, large values for capacitors such as in the millihenry range are generally avoided due to the fact that capacitors in the millifarads range are hard to obtain and not easily accessible. In fact, in this calculator, frequency values only from 1-3Hz utilize capacitors in the millifarad range. The rest of capacitors are in the microfarad range, which is much more easily accessible.

In general, low frequencies require very large capacitor and inductor values. As the value of the frequency increases, the values of the capacitors and inductor get much smaller. At very high frequencies, such as in the megahertz range, very small inductor and capacitors values are used. For frequencies 1MHz to 9.99MHz, capacitors in the nanofarads range and an inductor in the nanohenry range are used. For frequencies 10MHz or greater, capacitors in the picofarads and an inductor in the nanohenries is used.

This calculator can handle frequencies up to about 700MHz. After this, the capacitor values must fall below 1pF, which is impractical, because capacitors normally don't go below 1pF. And inductor values normally don't go below nanohenries. But 700MHz is high enough, which it normally is not necessary to obtain frequencies above this level.

A colpitts oscillator is very similar to a Hartley oscillator. The difference is that while a colpitts oscillator uses 2 capacitors and 1 inductor, a hartley oscillator uses 2 inductors and 1 capacitor. Colpitts oscillators are probably more cost effective than hartley oscillators, because inductors are more expensive and less available generally than capacitors. So obtaining capacitors is simple, which could make colpitts oscillators a more practical, cost-effective approach.

To use this calculator, a user simply has to enter the frequency desired. The frequency can be entered in hertz (Hz), kilohertz (KHz), and megahertz (MHz). The calculator will then compute the value of the 2 capacitors and the value of the inductor.

As stated, the colpitts oscillator may be built with an op amp, a transistor, or inverter logic chip, but its composition of 2 capacitors and an inductor is the same for each case. Therefore, this formula and calculator will work for any colpitts oscillator whether in a transistor, op amp, or inverter circuit.

Related Resources

Hartley Oscillator Calculator

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