“Clapp oscillator”的意思、由来-开放百科全书

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 Vačkář, 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 ({{math|C₀}}) 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

The capacitors {{math|C₁}} and {{math|C₂}} are usually much larger than {{math|C₀}}, so the {{math|1/C₀}} term dominates the other capacitances, and the frequency is near the series resonance of {{math|L}} and {{math|C₀}}. Clapp's paper gives an example where {{math|C₁}} and {{math|C₂}} are 40 times larger than {{math|C₀}}; the change makes the Clapp circuit about 400 times more stable than the Colpitts oscillator for capacitance changes of {{math|C₂}}.^[4]

Capacitors {{math|C₀}}, {{math|C₁}} and {{math|C₂}} 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 {{math|C₀}} a variable capacitor, Vačkář 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 {{math|f⁻³}}, so wide ranges will overdrive the amplifier. For VFOs, Vačkář recommends other circuits. See Vačkář oscillator.

References

1. ^{{cite journal |first=J. K. |last=Clapp |author1-link=James Kilton Clapp |title=An inductance-capacitance oscillator of unusual frequency stability |journal=Proc. IRE |volume=367 |issue= |pages=356-358 |date=March 1948 |ref=harv}}
2. ^{{cite report |first=Jiri |last=Vačkář |date=December 1949 |title=LC Oscillators and their Frequency Stability |publisher=Tesla National Corporation |location=Prague, Czechoslovakia |id=Tesla Technical Report |url=http://n1ekv.org/Oscillators/Vackar_wholepaper.pdf |accessdate=2008-12-20 |deadurl=yes |archiveurl=https://web.archive.org/web/20090124081121/http://n1ekv.org/Oscillators/Vackar_wholepaper.pdf |archivedate=2009-01-24 |df= |ref=harv}}
3. ^{{cite book |title=Basic Theory and Application of Transistors |date=1963 |origyear=1959 |author=Department of the Army |pages=171–173|id=TM 11-690 |publisher=Dover |quote=Modification of the Colpitts oscillator by including a capacitor in series with winding 1–2 of the transformer results in the Clapp oscillator.}}
4. ^{{harvnb|Clapp|1948|p=357}}
5. ^{{harvnb|Vačkář|1949|pp=5–6}}

History

Circuit

References

Further reading

External links