Oscillators – Plural oscillators – Oscillator used to vary amplitude or frequency of another...
Patent
1995-05-23
1996-06-11
Grimm, Siegfried H.
Oscillators
Plural oscillators
Oscillator used to vary amplitude or frequency of another...
331116FE, 331158, 331176, H03B 536, H03L 102
Patent
active
055259367
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a temperature-compensated oscillator circuit comprising an oscillator the output frequency of which has to be controlled, a processor the output of which is connected to the oscillator, counter means connected to at least one input of the processor and to temperature detecting oscillator means which are able to generate a temperature dependent signal.
Such a dual mode oscillator is known from DE-A-3.822.407.
Generally, crystal oscillators having a very high temperature stability are provided with a temperature compensating circuit. Such a circuit used to comprise a temperature sensor, a varicap and a control circuit, that could be analogue or digital. The calibration of such circuits in a temperature controlled measurement area took considerable time because the temperature-frequency characteristic is a function of higher order and, therefore, many points of the characteristic had to be measured. Moreover, because of limitations of a mechanical nature, the temperature-sensor needed for such a system, was always located at a distance from the crystal. Therefore, during the calibration procedure one had to observe a waiting time to guarantee the sensor and the crystal to have equal temperatures.
The temperature-compensated oscillator circuit according to DE-A3.822.407 mentioned above comprises a temperature detecting oscillator the frequency of which depends on the temperature. This circuit solves the problem of the waiting time during the calibration phase, however, the problem of non-linear relationship between the measured temperature and the frequency remains.
It is known as such that in oscillating crystals the frequency difference between a third harmonic frequency and three times the fundamental harmonic (f3--3*f1) exhibits a substantial linear temperature dependency. This feature is often used in temperature-compensated oscillator circuits, in, which, then, a dual mode oscillator is used which is able to oscillate on both the fundamental frequency and its third harmonic.
US-A-4.859.969 discloses a dual mode oscillator able to oscillate on both the fundamental frequency and its third harmonic. Such a dual mode oscillator is indicated to be suitable for use in clock driving circuits. However, a disadvantage of such a known dual mode oscillator is that a number of higher order filters is needed for the crystal to oscillate on both frequencies and to separate both signals afterwards. Because of these filters the circuit may only be integrated in a limited way.
The temperature-compensated oscillator circuit according to the invention is characterized in that the counter means comprises a first counter and a second counter, the input of the first counter being switchable through a first switch between first reference frequency means able to generate a first signal with a predetermined reference frequency and second reference frequency means able to generate a second signal with a reference equal to the predetermined reference frequency divided by three, the second counter being connected to said temperature detecting oscillator means which comprises a dual mode oscillator comprising a second, electronically controllable switch switchable between a first and a second state, wherein, during operation, said temperature detecting oscillator means will generate a third signal with a predetermined fundamental frequency in the first state and a fourth signal with a frequency substantially equal to the third harmonic of said fundamental frequency in the second state.
By the application of these features the linear temperature dependency of the difference between the frequency of the third harmonic and three times the fundamental frequency can be used both to control the temperature dependent oscillator and to calibrate it. The circuit according to the invention does not show the disadvantage of known dual mode oscillators as temperature detector means, e.g., as disclosed in US-A-4.859.969, since due to the switching capability between either an oscillation with the fundamental frequency or
REFERENCES:
patent: 4859969 (1989-08-01), Malinowski et al.
patent: 4872765 (1989-10-01), Schodowski
patent: 5004987 (1991-04-01), Hurley
patent: 5200714 (1993-04-01), Hayashi
Kamp Petrus J. M.
Post Reinder L.
Grimm Siegfried H.
Sierra Semiconductors B.V.
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