Английская Википедия:Clapp oscillator
The Clapp oscillator or Gouriet oscillator is an LC electronic oscillator that uses a particular combination of an inductor and three capacitors to set the oscillator's frequency. LC oscillators use a transistor (or vacuum tube or other gain element) and a positive feedback network. The oscillator has good frequency stability.
History
The Clapp oscillator design was published by James Kilton Clapp in 1948 while he worked at General Radio.[1] According to Czech engineer Jiří Vackář, oscillators of this kind were independently developed by several inventors, and one developed by Gouriet had been in operation at the BBC since 1938.[2]
Circuit
The Clapp oscillator uses a single inductor and three capacitors to set its frequency. The Clapp oscillator is often drawn as a Colpitts oscillator that has an additional capacitor (Шаблон:Math) placed in series with the inductor.[3]
The oscillation frequency in Hertz (cycles per second) for the circuit in the figure, which uses a field-effect transistor (FET), is
- <math>
f_0 = {1 \over 2\pi}
\sqrt{ {1 \over L}
\left( {1 \over C_0}
+ {1 \over C_1}
+ {1 \over C_2}
\right)} \ .
</math> The capacitors Шаблон:Math and Шаблон:Math are usually much larger than Шаблон:Math, so the Шаблон:Math term dominates the other capacitances, and the frequency is near the series resonance of Шаблон:Math and Шаблон:Math. Clapp's paper gives an example where Шаблон:Math and Шаблон:Math are 40 times larger than Шаблон:Math; the change makes the Clapp circuit about 400 times more stable than the Colpitts oscillator for capacitance changes of Шаблон:Math.[4]
Capacitors Шаблон:Math, Шаблон:Math and Шаблон:Math form a voltage divider that determines the amount of feedback voltage applied to the transistor input.
Although the Clapp circuit is used as a variable frequency oscillator (VFO) by making Шаблон:Math a variable capacitor, Vackář states that the Clapp oscillator "can only be used for operation on fixed frequencies or at the most over narrow bands (max. about 1:1.2)."[5] The problem is that under typical conditions, the Clapp oscillator's loop gain varies as Шаблон:Math, so wide ranges will overdrive the amplifier. For VFOs, Vackář recommends other circuits. See Vackář oscillator.
References
Further reading
- Ulrich L. Rohde, Ajay K. Poddar, Georg Böck "The Design of Modern Microwave Oscillators for Wireless Applications ", John Wiley & Sons, New York, NY, May, 2005, Шаблон:ISBN.
- George Vendelin, Anthony M. Pavio, Ulrich L. Rohde " Microwave Circuit Design Using Linear and Nonlinear Techniques ", John Wiley & Sons, New York, NY, May, 2005, Шаблон:ISBN.
- A. Grebennikov, RF and Microwave Transistor Oscillator Design. Wiley 2007. Шаблон:ISBN.
External links
- Шаблон:Commonscat-inline
- EE 322/322L Wireless Communication Electronics —Lecture #24: Oscillators. Clapp oscillator. VFO startup
