Oscillators – Solid state active element oscillator – Transistors
Patent
1987-08-13
1989-03-07
Laroche, Eugene R.
Oscillators
Solid state active element oscillator
Transistors
455318, H03B 500
Patent
active
048109762
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns improvements in or relating to the design of oscillators, expecially but not exclusively, oscillators suitable for use in heterodyne applications.
Implimentations of the invention, as discussed below, may be adapted, for example, for use in the tuning circuits of satellite communication receivers.
BACKGROUND ART
The operational frequency of oscillators is limited by the properties of transistors used and the technology adopted for their implimentation. Thus, for example, implimentations based upon conventional 3-micron size geometry, silicon material, bipolar technology are limited to operational frequencies at most just below to within the lower extreme of S-band (ie. the band 2-4 GH.sub.Z) operation. Hitherto, advance beyond this limit requires either considerable circuit complexity and high component count, or, resort to alternative and expensive advanced technologies, at present in their infancy, ie. smaller geometry and/or faster (ie. higher electron mobility semiconductor--eg. gallium-arsenide) material technologies.
It is known to employ oscillators in a dual purpose role in the construction of tuning circuits--ie. both as a local oscillator source and as a mixer. Applications here likewise are restricted by the frequency limit of the oscillator adopted.
It is of particular note that C-band transmission is specified as an International Standard for Satellite communications. There is an urgent need for oscillators and mixer-oscillators for this application, devices that can be produced with minimal complexity, at low cost, and that can be implimented using well-established and reliable process technology.
DISCLOSURE OF THE INVENTION
The invention, as disclosed herein, is intended to fulfill the need aforesaid. An oscillator is provided wherein signal at the second harmonic of the fundamental frequency can be generated, enhanced relative to signal at the fundamental frequency and, extracted as useful signal. This invention therefore, is an advance over oscillators implimented using the same technology, but capable only of producing useful signal of fundamental frequency.
In accordance with the present invention there is provided an oscillator, this oscillator being of a balanced configuration and comprising: transistor; transistor; the reactance shall appear as a shunt of negative resistance across the resonant network, and such as to sustain oscillation at network resonant frequency; and, extraction of useful enhanced signal at the second harmonic of the resonant frequency.
At resonance, and in the case of perfect matching, the signals output from the transistors have components at the fundamental resonant frequency that are equal in magnitude but in antiphase. These components therefore cancel at the summing node. The characteristic of each transistor is non-linear and harmonics are also generated. Signal components at odd harmonic frequency are likewise of equal magnitude and also in antiphase. These also cancel at the summing node. Signal components at the second harmonic and at other even harmonics are however in-phase and sum. The second harmonic signal is thus enhanced and produced as useful output.
In practical circumstances, matching is unlikely to be perfect. However, at the output node, signal at the resonant frequency will be significantly attenuated, and the signal at second harmonic frequency substantially enhanced as a result.
In the oscillator, defined above, it is of considerable advantage that signal at double the resonant frequency can be extracted as useful signal. Thus, for example, using 3 .mu.m silicon bipolar process technology, it is now possible to produce simple design, low component count oscillators, which produce useful signal at frequencies hitherto provided by fundamental oscillators of greater complexity and higher component count. In particular, it is possible not to design oscillators for C-band frequency operation using conventional bipolar devices.
Other advantages of the invention, and advantages of particular
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S. S. Walker et al. "Negative Resistance Oscillators with Inverse Hyperbolic Tangent Non-Linearities" IEEE International Symposium on Circuits and Systems vol. 3 May 2-4 1983, New York (US), pp. 1165-1168.
Cowley Nicholas P.
Lawton Rodney J.
McClelland Thomas D. S.
LaRoche Eugene R.
Pascal Robert J.
Plessey Overseas Limited
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