Patent ID: 6194972
Filing Date: 2001-02-27
Classification: H03B,H03H

Abstract:
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; andinductive 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 comprising first and second differential amplifiers, respectively, each differential amplifier having inverting and non-inverting inputs and outputs,the loop comprising 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 having a generally 90 degree phase shift between its input and output at the resonant frequency, each of the first and second differential amplifiers comprising a variable transconductance amplifier comprising tuning means and transconductance amplifying means, the transconductance amplifying means comprising first and second transistors for amplifying differential output from the differential amplifier, the tuning means tuning with differential voltage between the collectors of the first and second transistors.