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The Colpitts generator was unreal by yank engineer Edwin H. Colpitts in 1918. Colpitts generator works with a mixture of inductors associated capacitors by forming an LC filter. Same as different generators Colpitts oscillator consists of a gain device, and also the output is connected with associate LC circuit feedback circuit. The Colpitts generator may be a linear generator that produces a curving wave form.

The Tank Circuit

The main oscillation device in Colpitts generator is made victimisation the electrical circuit. The electrical circuit consists of 3 components- a electrical device and 2 capacitors. 2 capacitors ar connected serial, and these capacitors ar more connected in parallel with electrical device.

In the on top of image, 3 elements of the circuit ar shown with correct connections. the method starts with charging of 2 capacitors C1 and C2. Then within the circuit, these 2 series condensers discharge into the parallel inductance L1 and therefore the keep energy within the capacitor transferred to the inductance. thanks to the condenser connected in parallel, the inductance currently discharged by the 2 capacitors and therefore the capacitors begin to charge once more. These charging ANd discharging in each of the elements continues and therefore providing an oscillation signal across it.

The oscillation has very trusted the capacitors and therefore the inductor’s worth. Below formula is to work out the oscillation frequency:

F = 1 / 2π√LC

Where F is frequency and L is inductance, C is that the total equivalent capacitance.

The equivalent capacitance of the 2 capacitors is determined victimization

C = (C1 x C2) / (C1 + C2)

During this oscillation introduce the electric circuit, some energy loss occurs. To compensate for this lost energy and to sustain the oscillation within the electric circuit, a gain device is needed. There are many various styles of gain devices are accustomed to compensating for the loss of energy within the electric circuit. the foremost common gain devices ar transistors and operational amplifiers.

Transistors Based Colpitts Oscillator

In the higher than the image, the semiconductor|electronic transistor|semiconductor device|semiconductor unit|semiconductor} primarily based Colpitts generator is shown wherever the most gain device of the generator is associated NPN transistor T1.


In the circuit, electrical device R1 and R2 area unit needed for the bottom voltage. These 2 resistors area unit wont to create a potential divider across junction transistor T1’s base. electrical device R3 is employed as associate electrode electrical device. This electrical device is incredibly helpful to stable the gain device throughout the thermal drift. The electrical device C3 is employed as associate electrode bypass condenser that is connected in parallel with the electrical device R3. If we tend to take away this C3 electrical device, the amplified AC signal is dropped across electrical device R3 and ends up in a poor gain. So, the electrical device C3 is provided a simple path for the amplified signal. The feedback from the electric circuit is any connected exploitation the C4 to the junction transistor T1’s base.


The oscillation of the junction transistor primarily based Colpitts generator circuit is trusted the part shift. this can be documented as barkhausen criterion for the generator. As per the Barkhausen Criterion, the amplification ought to be slightly larger than the unity and also the part shift around the loop must be 360 degrees or zero degrees. So, throughout this case, to supply the oscillation across the output, the entire circuit desires zero degrees or 360-degree part shift. The junction transistor configuration as common electrode provides 180-degree part shift whereas the electric circuit conjointly contributes a further 180-degree part shift. By combining this two-phase shifts the entire electronic equipment achieves 360-degree part shift that is chargeable for the oscillation.


The feedback will be controlled exploitation the 2 capacitors C1 and C2. These 2 capacitors area unit connected serial and also the junction is any connection with the provision ground. The voltage across C1 is way larger than the voltage across C2. By dynamical those 2 electrical device values, we will manage the feedback voltage that is any fed back to the electric circuit. The determination of the feedback voltage could be a crucial a part of the electronic equipment as a result of the low quantity of feedback voltage wouldn’t activate the oscillation whereas a high quantity of feedback voltage can find yourself in destroying the output undulation and induce distortion.

The Colpitts generator is often tuned by dynamic the worth of inductance and capacitance. There area unit 2 ways that to create the Colpitts generator add a variable calibration configuration.


The first method is to vary the inductance as a variable inductance and therefore the alternative method is to vary the condensers as a variable capacitor. within the second possibility, because the feedback voltage is very dependable on the magnitude relation of C1 and C2 it’s better to use an easy gang. in order that once there’s variation in one condenser the opposite condenser additionally changes its capacitance in accordance with it.

Op-Amp Based Colpitts Oscillator

In the on top of image op-amp based mostly Colpitts generator circuit is shown. The operational electronic equipment is in inverting configuration mode. Resistors R1 and R2 area unit used thanks to offering the required feedback to the operational electronic equipment. The electric circuit is connected in conjunction with the one electrical device in parallel with 2 series capacitors. The input of the operational electronic equipment is connected to the feedback of the electric circuit.


The operating is that the same as mentioned within the on top of the semiconductor device based mostly Colpitts generator circuit. throughout startup, the op-amp amplifies noise signal that is accountable to charge 2 capacitors. The gain of Op-amp {based|based mostly|primarily based mostly} Colpitts generator is beyond the semiconductor device based Colpitts generator.

Difference between Colpitts Oscillator and Hartley Oscillator

The Colpitts generator is extremely kind of like Hartley generator however there’s a distinction in construction between these 2. though these 2 generator circuit consist 3 parts as a electrical circuit however the Colpitts generator uses one inductance in parallel with 2 capacitors asynchronous whereas the Hartley generator uses specifically opposite, one single electrical device in parallel with 2 inductors asynchronous. Colpitts generator performs additional stable in high-frequency operation than the Hartley generator.

The Colpitts oscillator is an excellent choice in high-frequency operation. It can produce output frequency in Megahertz range as well as in Kilohertz range.

Application of Colpitts Oscillator Circuit

  1. because of the difficulties during a swish variation of inductance and electrical condenser, the Colpitts generator is principally used for mounted frequency generation.
  2. the most use of Colpitts generator is in mobile or different frequency controlled communications devices.
  3. In high-frequency oscillation, Colpitts generator is a wonderful alternative. therefore high-frequency generator primarily based devices use Colpitts generator.
  4. during a few applications wherever continuous and undamped oscillation is required additionally with thermal stability, Colpitts generator is employed.
  5. For those applications which require a large variety of frequencies with minimum noise induced.
  6. many sorts of SAW-based sensors use Colpitts generator
  7. numerous kinds of sensing element use the Colpitts generator.
  8. FM connected frequency transmitter uses Colpitts generator.
  9. it’s an enormous application in military and industrial grade merchandise.
  10. In microwave applications, signal masking connected chaotic circuits is additionally needed Colpitts generator within the completely different frequency vary.