Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-02-04
2001-02-27
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S135000, C331S175000, C330S254000, C330S252000
Reexamination Certificate
active
06194972
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a gyrator forming a resonant circuit.
BACKGROUND INFORMATION
In modern communications systems, low phase noise oscillators are required as an integral part of the process of transporting data. While ever increasing data rates are employed, it becomes more and more difficult to meet the requirements for low phase noise. In many applications, the requirement for low phase noise has been met by means of oscillators with fixed frequencies or narrow band tuning range which utilizes some form of a resonant tank circuit of high quality factor (Q). The tank circuit limits the noise bandwidth of the oscillator circuit. In applications where a wider tuning range is needed, it is possible to use a multiple of such oscillators with overlapping tuning ranges. Such arrangements, however, are cumbersome and an alternative class of broad tuning range low noise integrated oscillator is desirable.
U.S. Pat. No. 5,371,475 granted to A. K. D. Brown on Dec. 6, 1994 describes the principles of operation of a class of low noise oscillators, which are known as gyrators. The principles of a conventional gyrator is fully described in the patent. U.S. Pat. No. 5,483,195 granted to A. K. D. Brown on Jan. 9, 1996 describes means of obtaining a broad tuning range for a gyrator oscillator which is independent of process and temperature variations. The prior gyrator needs improvement on achievement of broad tuning range concurrently with low phase noise, for some applications. A paper by A. K. D. Brown entitled “An integrated low power microwave VCO with sub-picosecond phase jitter”, IEEE 96CH35966, IEEE BCTM 10.3, pp. 165-168 describes phase noise analysis of gyrators.
SUMMARY OF THE INVENTIONS
It is an object of the present invention to provide a gyrator with an improved phase noise performance.
According to one aspect of the present invention, there is provided a gyrator forming a resonant circuit comprising: a loop having ports
1
and
2
, each port having two terminals, the loop comprising loop-connected first and second amplifiers, the gain of the loop being more than unity; capacitive means for coupling the terminals of the respective ports, thereby causing effective nodal capacitance in each port and effective nodal inductance in the other port, the capacitance and inductance determining the resonant frequency of the gyrator; and inductive means for coupling the terminals of the respective ports, thereby the effective nodal capacitance in the respective port being varied. The first and second amplifiers of the loop comprises first and second differential amplifiers, respectively, each differential amplifier having inverting and noninverting inputs and outputs. The loop comprises amplifier coupling means for coupling the inverting and non-inverting outputs of the first differential amplifier to the non-inverting and inverting inputs of the second differential amplifier, respectively, and for coupling the inverting and non-inverting outputs of the second differential amplifier to the inverting and non-inverting inputs of the first differential amplifier, respectively, the gain of the loop comprising the first and second differential amplifiers being greater than unity. Each of the first and second differential amplifiers has a generally
90
degree phase shift between its input and output at the resonant frequency.
For example, each of the first and second differential amplifiers comprises a variable transconductance amplifier. The variable transconductance amplifier comprises tuning means for tuning with a differential voltage. The variable transconductance amplifier further comprises automatic gain control means which is electrically separated from the tuning means. The tuning control means is functionally dependent upon the automatic gain control means. The automatic gain control means comprises a fast acting control loop to ensure oscillation stability under rapid tuning variations.
The gyrator further comprises a fast control loop and a slower control loop for precision vernier adjustment of an output signal level. An output oscillation frequency of the gyrator responds to the variation of the transconductance of the transconductance amplifiers.
REFERENCES:
patent: 5343162 (1994-08-01), Davis
patent: 5371475 (1994-12-01), Brown
patent: 5483195 (1996-01-01), Brown
patent: 5635880 (1997-06-01), Brown
patent: 6025765 (2000-02-01), Brown
patent: 0 669 710 (1995-08-01), None
“Design Considerations in High-Frequency CMOS Transconductance Amplifier Capacitor (TAC) Filters”, F. Krummenacher, Proc. of the International Symposium on Circuits and Systems, vol. 1, No. Symp.22, May 8, 1989, pp. 100-105.
“An Integrated Low Power Microwave VCO With Sub-picosecond Phase Jitter”, A.K.D. Brown, 1996 Proceedings of IEEE BCTM 10.3, Sep. 29-Oct. 1, 1996, Minneapolis, pp. 165-168.
de Wilton Angela C.
Kinkead Arnold
Nortel Networks Limited
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