Active tunable inductor

Details Active tunable inductor Active tunable inductor

1999-03-25

2001-04-03

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Negative resistance or reactance networks of the active type

Simulating specific type of reactance

C327S110000

Reexamination Certificate

active

06211753

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to tunable active inductors, particularly active inductors made using a monolithic radio frequency integrated circuit (RFIC).
BACKGROUND OF THE INVENTION
A significant restraint in RF and microwave IC design stems from the difficulty in realizing an integrated passive inductor with sufficiently high Q over a broad bandwidth. Large space requirements, low inductance values and low Q factors make these inductors unsuitable for precision applications.
Active designs have allowed larger inductance values to be realized. However, the active inductors published to date are limited in that they are often not tunable. When inductance tuning is introduced, the Q factor usually shows a strong dependence on both the tuning parameter and the frequency of operation. As a result, tuning both the inductance and the Q factor requires an iterative tuning procedure.
A Q-enhancing technique has been described by Tokumitsu et al in [1]. In this design a cascode FET arrangement with resistive feedback is used such that when the FETs are matched, the active inductor's loss resistance can be canceled. The resistive feedback described in [1] was replaced with a common gate FET in [2] which offered improved Q factor. everHow, tuning of Q of the inductance was not easily accomplished.
Alinikula et al [3] described an alternative topology to that given in [2] which offered greater tuning flexibility. With this technique the effect of finite channel conductance, g
ds
, was examined and a design was proposed which minimized sensitivity to g
ds
. Using a FET operating in its linear region as a variable resistor, the frequency at which maximum Q occurred could be controlled. For narrow bandwidths the Q factor approached 500, however, the loss resistance showed a strong frequency dependence.
A resonator design described by Haigh [4] introduced tuning of both the resonant frequency and the Q factor. A resonant circuit was formed by using two integrators terminated in a capacitance and connected in a feedback loop. Although the resonant frequency remained independent of Q tuning, the circuit showed a large loss resistance for frequencies below the resonant frequency.
Tuning control of both inductance and Q factor was also reported in a topology proposed by Lucyszyn and Robertson [5]. This design simulated an inductance that was adjustable over a narrow range of values by changing the gate bias voltage of a single FET. The Q factor could also be tuned to be maximum at an arbitrary frequency. However, as with the previous design, the loss resistance showed an appreciable frequency dependence resulting in very narrow band performance.
A more recent design presented by Yong-Ho et al [6] expanded on a common Q enhancement technique using a single FET with lossy inductive feedback. Instead of using a passive feedback inductor, an active inductor circuit was used in this design. The inductance was made tunable over a wide range by varying the loss resistance of the active feedback circuit. Tuning of the Q factor was accomplished by varying the positive supply voltage for all FETs and could only be set to infinity for a narrow band of frequencies. The loss resistance also varied over a wide range for frequencies outside of this narrow band.
List of References
1. T. Tokumitsu, T. Tanaka, M. Aikawa, S. Hara,
Broadband Monolithic Microwave Active Inductor And its Application to Miniaturized Wide
-
band Amplifiers
, in IEEE Trans. Microwave Theory Tech., vol 36, pp. 1920-1924, December 1988.
2. T. Tokurnitsu, M. Aikawa, S. Hara,
Lossless, Broadband Monolithic Microwave Active Inductors
, in IEEE MTT-S Symp. Dig., 1989, pp. 955-958
3. P. Alinikula, R. Kaunisto, K. Stadius,
Q
-
Enhancing Technique for High Speed Active Inductors
, in 1994 IEEE International Symposium on Circuits and Systems, pp. 735-738.
4. D. G. Haigh,
GaAs MESFET Active Resonant Circuit for Microwave Filter Applications
, in IEEE Trans. Microwave Theory Tech., vol 42, pp. 1419-1422, July 1994.
5. S. Lucyszyn, I. D. Robertson,
Monolithic Narrow
-
Band Filter Using Ultrahigh
-
Q Tunable Active Inductors
, in IEEE Trans. Microwave Theory Tech., vol 42, No. 12, pp. 2617-2622, December 1994.
6. C. Yong-Ho, H. Song-Cheol, K. Young-Se,
A Novel Active Inductor and Its Application to Inductance
-
Controlled Oscillator
, in EEE Trans. Microwave Theory Tech., vol 45, No.8, pp.1208-1213, August 1997.
SUMMARY OF THE INVENTION
In this patent document, a novel design for an active inductor is presented with more flexible tuning control than the prior art just described. It is an object of the invention to provide a series loss resistance of the simulated inductance that is frequency independent over a wide bandwidth. This constant resistance can be varied over a broad range of both positive and negative values with negligible impact on the effective inductance of the circuit. The inductance realized by the circuit is also tunable and remains independent of series loss tuning.
Thus, an active inductor is provided preferably implemented as a fully integrated GaAs MESFET active inductor.
Both the inductance and loss resistance are tunable with the inductance independent of series loss tuning. DC tuning of the loss resistance can also be achieved with complete independence of the loss resistance and inductance.
Bandwidth of the active inductor may be selected according to the fabrication technology employed and the intended application of the circuit.
According to an aspect of the invention, there is thus provided an active inductor formed as a monolithic integrated circuit. The active inductor has an input impedance that simulates an inductance with a loss resistance. The active inductor comprises a first capacitor and a second capacitor connected at a common voltage point V
2
, and each of the first capacitor and second capacitor being ungrounded. Circuit elements are arranged about the capacitors to provide voltage differentials across the capacitors, the voltage differentials being selected so that the loss resistance of the active inductor is tunable independently of the inductance of the active inductor. The circuit elements are preferably controlled sources, and the controlled sources are preferably implemented as MESFETs.
According to a further aspect of the invention, a negative impedance circuit is provided in parallel with the input of the active inductor. This increases the bandwidth of the active inductor.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.


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GaAs MESFET Active Resonant Circuit for Microwave Filter Applications, D.G. Haigh, IEEE: Transactions on Microwave Theory and Techniques, vol. 42, No. 7, Jul. 1994, P. 1419-1422.
Broad-Band Monolithic Microwave Active Inductor and Its application to Miniaturized Wide-Band Amplifiers, Shinji Hara, Tsuneo Tokumitsu, Toshiaki Tanaka, Masayoshi Aikawa, IEEE Transactions on Microwave Theory and Techniques, vol. 36, No. 12, Dec. 1988, p. 1920-1924.
Lossless Broad-Band Monolithic Microwave Active Inductors, Shinji Hara, Tsuneo Tokumitsu, Masayoshi Aikawa, IEEE Transactions on Microwave Theory and Techniques, vol. 37, No. 12, Dec. 1989, p. 1979-1984.
Monolithic Narrow-Band Filter Using Ultrahigh-Q Tunable Active Inductors, Stepan Lucyszyn, Ian D. Robertson, IEEE Transactions on Microwave Theory and Techniques, vol. 42, No. 12, Dec. 1994, p. 2617-2622.
Q-Enhancing Technique for High Speed Active Inductors, Risto Kaunisto, Petteri Alinikula, Kari Stadius, 1994 ISCA's, p. 735-738.
A Novel Active Inductor and Its Application to Inductance-Controlled Oscillator,

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