Patent ID: 7808752

Claim:
An apparatus for filtering a signal and for protecting an integrated circuit comprising: a passive filter electrostatic discharge circuit constructed on an integrated circuit, the passive filter electrostatic discharge circuit including: a first inductor that is formed as two series connected coils that are coaxially located about a first axis and on two different metal layers of the integrated circuit and separated by a dielectric layer with one of the coils of the first inductor overlaying the other coil wherein, responsive to a current passed through the first inductor, each coil of the first inductor generates a first magnetic field directionally aligned with a corresponding magnetic field generated by the other coil of the first inductor; a second inductor that is formed as two series connected coils that are coaxially located about a second axis different from the first axis and on the two different metal layers of the integrated circuit and separated by the dielectric layer with one of the coils of the second inductor overlaying the other coil wherein, responsive to a current passed through the second inductor, each coil of the second inductor generates a second magnetic field directionally aligned with a corresponding magnetic field generated by the other coil of the second inductor; a center point electrically connecting an exit node of the first inductor to an entry node of the second inductor; and a plurality of reverse-biased Zener diodes, each diode capacitively coupling an end of one coil of the passive filter electrostatic discharge circuit to a substrate, the plurality of reverse-biased Zener diodes providing capacitance for the passive filter electrostatic discharge circuit and providing electrostatic discharge protection to another integrated circuit, wherein the first inductor, the second inductor and the plurality of reverse-biased Zener diodes together form a multi-pole passive filter having a filter passband with a filter cut-off frequency, wherein the second inductor is located adjacent to the first inductor, wherein a current of the signal, passing through one, then the other of the first and second inductors, generates a magnetic field in each inductor that is mutually and negatively coupled with the magnetic field in the other inductor, and wherein the negative coupling of the magnetic fields increases a roll-off rate of the filter cut-off frequency at an upper frequency edge of the filter passband of the multi-pole passive filter, thereby improving rejection band performance for the passive filter electrostatic discharge circuit.