Kolpitsa generator

Historical scheme

The Kolpitz generator (capacitive three-point), named after its inventor Edwin Kolpitz, is one of the many circuits of electronic generators using a combination of inductance (L) with capacitance (C) to determine the frequency, also called an LC generator. One of the key features of this type of generators is their simplicity (only one inductance without taps is needed).

Feedback voltage is removed from the capacitive voltage divider.

Generation Frequency

Fig. 1: Simple Kolpitz generator with a common base (with simplified bias circuits)

Equivalent Kolpitz Generator Circuit

The ideal generation frequency for the circuit in Fig. 1 is determined by the equation:

f_{0}={1 \over 2\pi {\sqrt {L\cdot \left({C_{1}\cdot C_{2} \over C_{1}+C_{2}}\right)}}}

{\ displaystyle f_ {0} = {1 \ over 2 \ pi {\ sqrt {L \ cdot \ left ({C_ {1} \ cdot C_ {2} \ over C_ {1} + C_ {2}} \ right )}}}}

Valid circuits generate a slightly lower frequency.

Fig. 3: Practical circuit of the Kolpitz generator with a common base (with a generation frequency of ~ 50 MHz)

Kolpitsa generator in a cascade with a common base

Kolpitz generator on an operational amplifier

Depending on the amplifier cascade scheme, three types of Kolpitz generator are possible: on the cascade with a common emitter, on the cascade with a common collector and on the cascade with a common base. A characteristic feature of the Kolpitz generator is the positive feedback through a capacitive voltage divider on two series capacitors, which are simultaneously the capacity of the LC circuit.

The Kolpitz generator circuit in a cascade with a common base is the most high-frequency (Fig. 1, Fig. 3). A cascade with a common base does not shift the phase. The LC1C2 circuit is fully connected to the collector. Full inclusion of the circuit does not shift the phase. The emitter is connected to the circuit to the midpoint of the capacitive voltage divider with phase imbalance, with equal C1 and C2 the phase imbalance and the loop phase shift is 45 °. In addition, a 60 ° shift creates an RC circuit formed by the equivalent capacitance of capacitors C1 and C2 and resistor R, which complicates the calculation of the resulting shift.

The Kolpitz generator circuit in a cascade with a common emitter is shown in Fig. 8.1.b) in Fig . 8.1.b) .

The Kolpitts generator circuit in a cascade with a common collector is shown in Fig . 8.2 . A cascade with a common collector does not shift the phase. The LC1C2 circuit is connected to the base without phase distortion. The emitter is connected to the circuit with phase imbalance, at the same values of C1 and C2, the phase imbalance and the loop phase shift is 45 °. The phase stability margin is -135 ° ÷ + 45 °, but the emitter circuits in this case strongly shunt the circuit.

A variation of the Kolpitz generator with a second capacitive voltage divider is the Vachkar generator .

Links

http://radiomaster.ru/stati/radio/gen.php Fig. 1.3 Kolpitts generator. Fig. 1.6 Quartz crystal oscillator.
https://web.archive.org/web/20091229122251/http://logic-bratsk.ru/radio/ewb/ewb2/CHAPTER2/2-8/2-8-1/2-8-1.htm Fig .8.1. (B) Capacitive three-point circuit or Kolpitts circuit. Fig. 8.2. Kolpitsa generator. Figure 8.4 Kolpitz generator with coupling capacitor.
http://konspektiruem.ru/articles/electronics/Generatory_sinusoidalnyh_kolebanii/ Fig. 3.2.2 Kolpitsa generator
https://web.archive.org/web/20090906101428/http://sheme.edu.knu.kg/contents/ch7b.htm 7.8 Non-linear analog circuits. Harmonic and pulse generators. (Kolpits generator)
http://www.falstad.com/circuit/index.html Circuits. Transistors. Oscillators. Colpitts Oscillator
http://easyradio.ru/spravochnik/empiricheskiy_raschet_vch_generatora_na_bipolyarnom_tranzistore.html Empirical calculation of an RF LC generator using a bipolar transistor

Kolpitsa generator

Generation Frequency

See also

Links

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