Highly selective passive filters using low-Q planar capacitors and inductors
First Claim
1. An electrical frequency filter having a characteristic selective transfer function, said electrical frequency filter comprisingat least one planar capacitor,at least two inductively coupled planar inductors, each of which has a loss quality factor, Q, of less than approximately 20, and neither of which is shorted,wherein said inductively coupled planar inductors overlap and provide a mutual inductance expressed in terms of a coupling coefficient, K, andwherein the at least two planar inductors are arranged to achieve a coupling coefficient, K, that for said planar inductors, along with selected capacitance and inductance values for the at least one capacitor and the at least two inductors of the electrical frequency filter, achieves a selective transfer function in a passive circuit topology without loss cancellation circuitry.
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Abstract
A highly selective frequency filter is created from lossy components such as found in standard integrated circuit technologies, including particularly CMOS technologies, without the use of active loss cancellation circuitry. The filter configuration is based on using inductively coupled planar inductors for introducing a mutual inductance factor that advantageously alters the frequency response of the filter.
15 Citations
15 Claims
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1. An electrical frequency filter having a characteristic selective transfer function, said electrical frequency filter comprising
at least one planar capacitor, at least two inductively coupled planar inductors, each of which has a loss quality factor, Q, of less than approximately 20, and neither of which is shorted, wherein said inductively coupled planar inductors overlap and provide a mutual inductance expressed in terms of a coupling coefficient, K, and wherein the at least two planar inductors are arranged to achieve a coupling coefficient, K, that for said planar inductors, along with selected capacitance and inductance values for the at least one capacitor and the at least two inductors of the electrical frequency filter, achieves a selective transfer function in a passive circuit topology without loss cancellation circuitry.
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7. An electrical frequency bandpass filter having a characteristic selective transfer function, said electrical frequency filter comprising
at least two inductively coupled resonators having reactive components including lossy planar inductors characterized by a loss quality factor, Q, wherein neither of said lossy planar inductors is shorted, said inductively coupled resonators being inductively coupled by overlapping the lossy planar inductors having a coupling coefficient, K, established by setting the physical overlap of said inductors of the coupled resonators, wherein the physical overlap between the coupling lossy planar inductors of said resonators is set to achieve a coupling coefficient, K, that, along with selected values for the other reactive components of the electrical frequency bandpass filter, achieves a selective transfer function in a passive circuit topology without loss cancellation circuitry.
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9. A method of creating a selective electrical frequency filter without loss cancellation circuitry, wherein the selective electrical frequency filter has a characteristic frequency response and is comprised of lossy planar inductors and planar capacitors, said method comprising
a. establishing an upper and lower frequency response template for the a desired frequency response for the selective electrical frequency filter, b. using said templates to calculate a set of coefficients that formulate the geometric characteristics of the capacitors, inductors, and the coupling between the capacitors and inductors, for a filter circuit topology necessary select to estimate the order of the electrical frequency filter needed to fit the filter'"'"'s frequency response within said upper and lower frequency response templates, c. establishing a circuit model for the order of filter selected, said circuit model having circuit components including at least two mutually coupled inductors, at least one capacitor, and resistors representing the loss mechanisms of the circuit components, and wherein the mutual inductance between said mutually coupled inductors is represented by a coupling coefficient, K, d. establishing component values for the circuit components of the circuit model and the coupling coefficient, K, of the mutually coupled inductors, e. determining whether the response of said circuit model fits within the upper and lower frequency response template for the desired frequency response for the selective electrical frequency filter, and if it does not selecting another order for the electrical frequency filter and repeating steps (c) through (e) until a circuit model with component values and a coupling coefficient, K, for the mutually coupled inductors is achieved that fits the desired frequency response, f. determining the geometric characteristics of the lossy planar inductors and planar capacitors for the electrical frequency filter based on the component values of the circuit model established by the foregoing steps, including determining the relative placement of the mutually coupled planar inductors needed to achieve the coupling coefficient, K, and g. creating an electrical frequency filter based on lossy planar inductors and planar capacitors having geometric characteristics, including the placement of the mutually coupled inductors, determined in accordance with step (f).
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14. An electrical frequency filter having a selective transfer function, said electrical frequency filter comprising
at least two lossy planar inductors, wherein the loss quality factor, Q, of each of said lossy planar spiral inductors is less than approximately 20, and wherein neither of said lossy planar inductors is shorted, at least one planar capacitor connected to each of said planar inductors, the planar inductors being arranged in overlapping relation to provide mutual inductance therebetween, wherein the mutual inductance between the lossy planar inductors, along with the capacitance and inductance values for said planar capacitors and planar inductors, achieves a selective transfer function in a passive circuit topology without loss cancellation circuitry.
Specification