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The Clapp oscillator or Gouriet oscillator is an
LC electronic oscillator that uses a particular combination of an
inductor
An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...
and three
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s to set the oscillator's frequency. LC oscillators use a
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
(or
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as ...
or other gain element) and a
positive feedback
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in th ...
network. The oscillator has good frequency stability.
History
The Clapp oscillator design was published by
James Kilton Clapp
James Kilton Clapp (December 30, 1897 – 1965) was an American electrical engineer who worked for General Radio Corporation. He was born in Denver, Colorado and graduated from Massachusetts Institute of Technology in 1923, obtaining a master's de ...
in 1948 while he worked at
General Radio
General Radio Company (later, GenRad) was a broad-line manufacturer of electronic test equipment in Massachusetts, U.S. from 1915 to 2001.
History
On June 14, 1915, Melville Eastham and a small group of investors started General Radio Company ...
. 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
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...
since 1938.
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 A Colpitts oscillator, invented in 1918 by American engineer Edwin H. Colpitts, is one of a number of designs for LC oscillators, electronic oscillators that use a combination of inductors (L) and capacitors (C) to produce an oscillation at a certa ...
that has an additional capacitor () placed in series with the inductor.
The oscillation frequency in Hertz (cycles per second) for the circuit in the figure, which uses a field-effect transistor (
FET
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contr ...
), is
:
The capacitors and are usually much larger than , so the term dominates the other capacitances, and the frequency is near the series resonance of and . Clapp's paper gives an example where and are 40 times larger than ; the change makes the Clapp circuit about 400 times more stable than the Colpitts oscillator for capacitance changes of .
Capacitors , and 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 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)."
The problem is that under typical conditions, the Clapp oscillator's loop gain varies as , 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, .
* George Vendelin, Anthony M. Pavio, Ulrich L. Rohde " Microwave Circuit Design Using Linear and Nonlinear Techniques ", John Wiley & Sons, New York, NY, May, 2005, .
* A. Grebennikov, RF and Microwave Transistor Oscillator Design. Wiley 2007. .
External links
*
EE 322/322L Wireless Communication Electronics—Lecture #24: Oscillators. Clapp oscillator. VFO startup
{{DEFAULTSORT:Clapp Oscillator
Electronic oscillators