Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2002-11-25
2003-12-02
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000
Reexamination Certificate
active
06657483
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to filters, and more specifically to a method and apparatus for adjusting the trans-conductance of a filter.
2. Related Art
A filter generally refers to a component which allows/passes a range of frequencies and rejects all other frequencies from an input signal. For example, a low pass filter allows all low frequencies below a cut off frequency (determined by filter components) and rejects all the high frequencies above cut off frequency.
Filters are often implemented within integrated circuits, and are thus characterized by trans-conductance. Trans-conductance generally provides a measure of the degree of conductivity of a filter and equals the reciprocal of resistance. Filter characteristics such as frequency response and amplification factor are determined by (among other factors) the trans-conductance value as is well known in the relevant arts.
One problem often encountered with filters is that the actual trans-conductance value is at variance with a desired value. The variance can be for reasons such as imperfections in manufacturing technologies and material, changes in operating conditions (e.g., ambient temperature), etc. Accordingly, it is desirable to adjust the trans-conductance value of a filter during operation.
SUMMARY OF THE INVENTION
A tuning circuit provided according to an aspect of the present invention can be used to tune a component (e.g., filter) to a desired trans-conductance value. The tuning circuit may contain a trans-conductor circuit generating a present signal representing a present trans-conductance of the trans-conductor circuit. The trans-conductance circuit operates to provide a similar transfer function as the component. A reference circuit may generate a reference signal representing the desired trans-conductance value.
An integrating capacitor may receive both the present signal and the reference signal in opposite directions, and be charged to a voltage level representing a difference of the present signal and the reference signal. An amplifier may amplify the voltage level to generate an analog signal. The analog signal may then be used to change the trans-conductance of the trans-conductor circuit and the component.
Due to the operation of the integrating capacitor, the tuning circuit may be implemented using only a single active element (i.e., amplifier). The amplifier can be implemented in an open loop configuration to minimize power consumption. In an embodiment, the amplifier is implemented as a single stage CMOS amplifier.
In an embodiment, the reference signal is generated using a switched capacitor circuit. The tuning circuit may further contain a passive circuit (i.e., containing only passive elements) to eliminate any ripple generated in a voltage signal generated by the switched capacitor circuit.
In an embodiment, the passive circuit contains a first resistor connected in parallel to the integrating capacitor, the first resistor and the integrating capacitor being connected between a first node and a second node. The passive circuit may also contain a second resistor connected between the non-inverting input terminal of the amplifier and the first node. A third resistor may be connected between the inverting input terminal (of the amplifier) and the second node.
More passive components may be provided to eliminate (reduce) any additional ripples present at the output of the amplifier. In an embodiment, a second capacitor, a fifth resistor and a third capacitor may be provided. The second capacitor is connected between the output terminal of the amplifier and a ground, the fifth resistor is connected between the output terminal of the amplifier and a third node, and the third capacitor is connected between the third node and the ground.
In an embodiment, the output of the amplifier may not be stable due to the two poles respectively introduced by the integrating capacitor and the amplifier. Accordingly, the tuning circuit may be provided with a fourth resistor and a first capacitor connected in series between the output terminal and the ground. The fourth resistor and the first capacitor operate to remove the effect of one of the poles by introducing a zero, thereby lending stability to the output signal.
The tune component (e.g., filter) may contain multiple trans-conductor stages. The output of the amplifier may be examined to determine the specific stages to activate and de-activate. A digital bits generator may generate digital bits specifying which ones of the stages to be activated and de-activated.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.
REFERENCES:
patent: 5650950 (1997-07-01), Siniscalchi et al.
patent: 6172569 (2001-01-01), McCall et al.
Francois Krummenacher and Norbert Joehl, “A 4-MHz CMOS Continuous-Time Filter with On-Chip Automatic Tuning”, IEEE Journal of Solid State Circuits, vol. 23, No. 3, Jun. 1988, pp. 750-758.
Chin S. Park and Rolf Schaumann, “Design of a 4MHz Analog Integrated CMOS Transconductance -C Bandpass Filter”, IEEE Journal of Solid State Circuits, vol. 23, No. 4, Aug. 1988, pp. 987-996.
J. Silva Martinez, Michiel Steyaert and Willy Sansen, A Novel Approach for the Automatic Tuning of Continuous Time Filters, IEEE Intenational Symposium in Circuits and Systems, 1991, pp. 1452-1455.
Un-Ku Moon and Bang- Sup Song, “Design of a Low-Distortion 22 kHz Fifth-Order Bessel Filter”, IEEE Journal of Solid State Circuits, vol. 28,No. 12, Dec. 1993, pp. 1254-1264.
Un-Ku Moon and Bang- Sup Song, “A Low-Distortion 22 kHz 5th-Order Bessel Filter”, IEEE International Solid-State Circuits Conference 1993, pp. 110-111, 271.
Srinivasan Venkatraman, Srikanth Natarajan, K. Radhakrishna Rao, “A New Tuning Scheme for Continuous Time Filters”, 1063-9667/97, 1997 IEEE, pp. 150-154.
Scott T. Dupuie and Mohammen Ismail, High Frequency CMOS Transconductors, Book title:“Analogue IC design : The current mode Approach”—by C. Toumazou, Chapter 5, pp. 181-231, Publisher:Peter Peregrinus Ltd; ISBN number is 0 86341 215 7.
Brady III W. James
Le Dinh T.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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