Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2000-06-13
2001-11-06
Grimm, Siegfried H. (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S1160FE, C331S158000
Reexamination Certificate
active
06313712
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to oscillators which generate radio frequency signals. Specifically, a crystal oscillator for low power applications is described having improved long term and short term frequency stability.
Crystal oscillators have been used for many years as the signal generators for generating frequency stable radio frequency signals. The proliferation of low power communication devices, such as cellular telephones, has placed additional constraints on oscillator design since a major objective of the design is to preserve battery life. In applications such as the cellular telephones, a frequency synthesizer may typically be used to generate a local oscillator signal for the superhetrodyne receiver within the telephone. The frequency synthesizer as is well known relies upon a stable source of radio frequency signals from which to synthesize other signals needed in the frequency conversion process for the telephone receiver. The source of radio frequency signals must have good long term stability, i.e., the frequency drift must be within a tolerable range, as well as a high short term stability constituting the noise floor for the radio frequency signal.
SUMMARY OF THE INVENTION
An oscillator circuit is provided having a high long term frequency stability as well as short term frequency stability in a low power radio frequency generator. The oscillator circuit achieves long term stability by maintaining a low amplitude drive signal across a frequency control element to lower the power dissipation in the frequency control element. The oscillator circuit has few active elements which would otherwise reduce the oscillator's short term stability.
In a preferred embodiment of the invention, a source follower is connected to drive a bipolar transistor. Feedback is provided through a frequency control element connected between the bipolar transistor collector-emitter circuit and the source follower input. The current level through the bipolar transistor is established by a current source which sets the drive voltage for the frequency control element. An output terminal is connected to the source follower input which produces a radio frequency signal having lower distortion and consequently a reduced amount of phase noise.
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Mourant Jean-Marc
Shkap Daniel
Connoly Bove Lodge & Hutz
Grimm Siegfried H.
International Business Machines - Corporation
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