Narrow band-pass tuned resonator filter topologies having high selectivity, low insertion loss and improved out-of-band rejection over extended frequency ranges
First Claim
1. A circuit comprising:
- a first resonator magnetically coupled to a second resonator, said first and second resonator each further comprising;
a first capacitor having a first capacitance and a first inductive element having a first inductance connected between a signal line and ground;
a second capacitor having a second capacitance and a second inductive element having a second inductance connected between said signal line and ground so that current flowing through said first and second inductive elements are substantially in opposite directions;
wherein said first and second inductive elements are magnetically coupled; and
wherein the product of said first capacitance and said first inductance is substantially equal to the product of said second capacitance and said second inductance.
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Abstract
A tuned resonator circuit topology is disclosed that permits implementation of narrow band-pass filters having high loaded Q and optimal coupling (for low insertion loss) using a parallel tuned resonator topology at frequencies in the 1 to 2 GHz range and beyond. The topology consists of a mirror image of the parallel tuned circuit about the signal line of a conventional parallel tuned circuit to effect a cancellation of virtually all of the induced currents between the inductive elements of the resonators. This reduction in induced currents reduces the magnetic coupling between the resonators, thereby offsetting the increase in overall coupling between the resonators as frequency increases, and thereby serves to maintain optimal coupling between the resonators as the frequency of operation increases. Moreover, the mirror image topology increases the parallelism between the inductive elements in the resonators, thereby decreasing the inductance values and permitting an increase in capacitance values. Increasing the capacitance values of the resonators effectively offsets the decrease in the loaded Q as frequency is increased. The topology works for any number of parallel resonators. As the resolution of the manufacturing process decreases (e.g. from printed circuit board to integrated circuit processes), the range of operating frequencies scales with the increase in resolution.
23 Citations
20 Claims
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1. A circuit comprising:
a first resonator magnetically coupled to a second resonator, said first and second resonator each further comprising;
a first capacitor having a first capacitance and a first inductive element having a first inductance connected between a signal line and ground;
a second capacitor having a second capacitance and a second inductive element having a second inductance connected between said signal line and ground so that current flowing through said first and second inductive elements are substantially in opposite directions;
wherein said first and second inductive elements are magnetically coupled; and
wherein the product of said first capacitance and said first inductance is substantially equal to the product of said second capacitance and said second inductance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A circuit comprising:
two or more resonators magnetically coupled to each other in cascade, said two or more resonators each further comprising;
a first capacitor having a first capacitance and a first inductive element having a first inductance coupled between a signal line and ground;
a second capacitor having a second capacitance and a second inductive element having a second inductance coupled between said signal line and ground so that current flowing through said first and second inductive elements are substantially in opposite directions; and
wherein said first and second inductive elements are magnetically coupled. - View Dependent Claims (10, 11, 12, 13, 14, 17, 18)
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15. A method of maintaining high loaded Q and optimal coupling for a parallel-tuned series resonant circuit having a resonant frequency selected over an extended frequency range, the circuit having two or more tuned resonators magnetically coupled to one another in cascade, each of the resonators comprising an inductive element connected between a signal line and ground and having an inductance of L, and a capacitance element connected between the signal line and ground and having a capacitance of C, said method comprising the steps of:
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implementing the inductive elements each as a bulk inductance formed by metal lines over a substantially nonconductive surface;
canceling out substantially the mutually induced currents between the two or more resonators by setting the physical proximity and orientation of the metal lines of said inductive elements in a manner that reduces the respective inductances of said inductive elements;
selecting an increased value of C so as to achieve resonance with the reduced value of L at said resonant frequency; and
controlling the coupling between the two or more resonators by setting the physical distance between the two or more resonators in proportion to the size of the inductive elements. - View Dependent Claims (16)
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19. A circuit comprising:
two or more resonators magnetically coupled to each other in cascade, said two or more resonators each further comprising;
a first capacitor having a first capacitance and a first inductive element having a first inductance coupled between a signal line and ground;
a second capacitor having a second capacitance and a second inductive element having a second inductance coupled between said signal line and ground so that current flowing through said first and second inductive elements are substantially in opposite directions; and
wherein said first and second inductive elements of each of said two or more resonators are romantically coupled to the first and second inductive elements of each of the two or more resonators with which it is coupled in cascade.
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20. A circuit comprising:
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a first resonator magnetically coupled to a second resonator, said first and second resonator each further comprising;
a first capacitor having a first capacitance and a first inductive element having a first inductance connected between a signal line and ground;
a second capacitor having a second capacitance and a second inductive element having a second inductance connected between said signal line and ground so that current flowing through said first and second inductive elements are substantially in opposite directions; and
wherein the product of said first capacitance and said first inductance is substantially equal to the product of said second capacitance and said second inductance; and
wherein said first and second inductive elements of said first resonator are magnetically coupled to the first and second inductive elements of said second resonator.
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Specification