# US 10,374,572 B2 · Radiofrequency filter with improved attenuation of common mode signals > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,374,572 B2 - Document ID: US10374572B2 - Status: Granted - Kind: B2 - Application number: 15/727,582 - Filed: 2017-10-07 - Published: 2018-04-19 - Granted: 2019-08-06 - Earliest claimed: 2016-10-14 - Applicants: John Gordon Ramsey - Inventors: John Gordon Ramsey - Web page: https://patentgrep.com/patent/US10374572B2 ## CPC - H03H 7/427: {Common-mode filters (H02J3/01 and H02M1/126 takes precedence)} - H01P 1/225: {Coaxial attenuators (H01P1/23 takes precedence)} - H01R 13/659: with plural ports for distinct connectors - H03H 7/00: Multiple-port networks comprising only passive electrical elements as network components - H03H 7/09: Filters comprising mutual inductance - H05K 9/0066: {Constructional details of transient suppressor} - H05K 9/0069: {Methods for measuring the shielding efficiency; Apparatus therefor; Isolation container for testing} - H01P 1/207: Hollow waveguide filters (H01P1/212, H01P1/213, H01P1/215, H01P1/219 take precedence) - H03H 1/0007: {of radio frequency interference filters} - H04B 15/02: Reducing interference from electric apparatus by means located at or near the interfering apparatus - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - H01P: WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE (operating at optical frequencies G02B) - H01R: ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS - H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS - H04B: TRANSMISSION ## Abstract A radiofrequency filter utilizing a common mode choke both as a traditional common mode choke as well as the inductance in a low pass filter. Filter topology as well as component selection is optimized for wide band operation. Common mode chokes allow differential currents to pass with little attenuation while common mode currents are effectively presented with an inductance in the common current path. This inductance is used in a low pass filter configuration to present an even higher attenuation to common mode currents. The use of multiple chokes and/or differing core materials contributes to wider band operation without pronounced resonances. The capacitance used in the low pass filter is connected in a way as to reduce its effect on the data signals while still being effective in filtering. ## Claims ### Claim 1 A radiofrequency filter circuit comprising: a first input terminal and a second input terminal; a first output terminal and a second output terminal; a first signal path between the first input terminal and the first output terminal; a second signal path between the second input terminal and the second output terminal; a first common mode choke having a first set of bifilar windings and a second set of bifilar windings and a second common mode choke having a first set of bifilar windings and a second set of bifilar windings where the first set of bifilar windings on the first common mode choke is in series with the first set of bifilar windings on the second common mode choke such that the first set of bifilar windings on the first common mode choke in series with the first set of bifilar windings on the second common mode choke are in the first signal path between the first input terminal and the first output terminal and where the second set of bifilar windings on the first common mode choke is in series with the second set of bifilar windings on the second common mode choke such that the second set of bifilar windings on the first common mode choke in series with the second set of bifilar windings on the second common mode choke are in the second signal path between the second input terminal and the second output terminal; a first capacitive structure in the first signal path between the first input terminal and the first output terminal and electrically connected at a point between the first set of bifilar windings on the first common mode choke and the first set of bifilar windings on the second common mode choke and ground; a second capacitive structure in the second signal path between the second input terminal and the second output terminal and electrically connected at a point between the second set of bifilar windings on the first common mode choke and the second set of bifilar windings on the second common mode choke and ground; and a third common mode choke having a first set of bifilar windings and a second set of bifilar windings where the first set of bifilar windings of the third common mode choke is connected in series with the first capacitive structure and the second set of bifilar windings of the third common mode choke is connected in series with the second capacitive structure. ### Claim 2 (depends on 1) The radiofrequency filter circuit of claim 1, wherein the first capacitive structure and the second capacitive structure are microstriplines comprising additional pad area. ### Claim 3 (depends on 1) The radiofrequency filter circuit of claim 1, wherein the bifilar windings on the first common mode choke and the bifilar windings on the second common mode choke present a nominal 90 ohm balanced line impedance. ### Claim 4 (depends on 1) The radiofrequency filter circuit of claim 1, wherein the first set of bifilar windings and the second set of bifilar windings for the first common mode choke are each wound with three turns around a core. ### Claim 5 (depends on 1) The radiofrequency filter circuit of claim 1, wherein the first set of bifilar windings and the second set of bifilar windings for the second common mode choke are each wound with three turns around a core. ### Claim 6 (depends on 1) The radiofrequency filter circuit of claim 1, wherein the first set of bifilar windings and the second set of bifilar windings for the third common mode choke are each wound with three turns around a core. ### Claim 7 A universal serial bus (USB) filter circuit comprising: a first radiofrequency filter circuit, a second radiofrequency filter circuit and a third radiofrequency filter circuit; wherein each radiofrequency filter circuit comprises: a first input terminal and a second input terminal; a first output terminal and a second output terminal; a first signal path between the first input terminal and the first output terminal; a second signal path between the second input terminal and the second output terminal; a first common mode choke having a first set of bifilar windings and a second set of bifilar windings and a second common mode choke having a first set of bifilar windings and a second set of bifilar windings where the first set of bifilar windings on the first common mode choke is in series with the first set of bifilar windings on the second common mode choke such that the first set of bifilar windings on the first common mode choke in series with the first set of bifilar windings on the second common mode choke are in the first signal path between the first input terminal and the first output terminal and where the second set of bifilar windings on the first common mode choke is in series with the second set of bifilar windings on the second common mode choke such that the second set of bifilar windings on the first common mode choke in series with the second set of bifilar windings on the second common mode choke are in the second signal path between the second input terminal and the second output terminal; a first capacitive structure in the first signal path between the first input terminal and the first output terminal and electrically connected at a point between the first set of bifilar windings on the first common mode choke and the first set of bifilar windings on the second common mode choke and ground; a second capacitive structure in the second signal path between the second input terminal and the second output terminal and electrically connected at a point between the second set of bifilar windings on the first common mode choke and the second set of bifilar windings on the second common mode choke and ground; and a third common mode choke having a first set of bifilar windings and a second set of bifilar windings where the first set of bifilar windings of the third common mode choke is connected in series with the first capacitive structure and the second set of bifilar windings of the third common mode choke is connected in series with the second capacitive structure. ### Claim 8 (depends on 7) The universal serial bus (USB) filter circuit of claim 7, wherein the first set of bifilar windings and the second set of bifilar windings for the third common mode choke are each wound with three turns around a core. ### Claim 9 (depends on 7) The universal serial bus (USB) filter circuit of claim 7, wherein the first capacitive structure and the second capacitive structure are microstriplines comprising additional pad area. ### Claim 10 (depends on 7) The universal serial bus (USB) filter circuit of claim 7, wherein the bifilar windings on the first common mode choke and the bifilar windings on the second common mode choke present a nominal 90 ohm balanced line impedance. ### Claim 11 (depends on 7) The universal serial bus (USB) filter circuit of claim 7, wherein the first set of bifilar windings and the second set of bifilar windings for the first common mode choke are each wound with three turns around a core. ### Claim 12 (depends on 7) The universal serial bus (USB) filter circuit of claim 7, wherein the first set of bifilar windings and the second set of bifilar windings for the second common mode choke are each wound with three turns around a core. ### Claim 13 A radiofrequency filter circuit comprising: a first input terminal and a second input terminal; a first output terminal and a second output terminal; a first signal path between the first input terminal and the first output terminal; a second signal path between the second input terminal and the second output terminal; a first common mode choke having a first set of bifilar windings and a second set of bifilar windings and a second common mode choke having a first set of bifilar windings and a second set of bifilar windings where the first set of bifilar windings on the first common mode choke is in series with the first set of bifilar windings on the second common mode choke such that the first set of bifilar windings on the first common mode choke in series with the first set of bifilar windings on the second common mode choke are in the first signal path between the first input terminal and the first output terminal and where the second set of bifilar windings on the first common mode choke is in series with the second set of bifilar windings on the second common mode choke such that the second set of bifilar windings on the first common mode choke in series with the second set of bifilar windings on the second common mode choke are in the second signal path between the second input terminal and the second output terminal; a first capacitive structure in the first signal path between the first input terminal and the first output terminal and electrically connected at a point between the first set of bifilar windings on the first common mode choke and the first set of bifilar windings on the second common mode choke and ground; a second capacitive structure in the second signal path between the second input terminal and the second output terminal and electrically connected at a point between the second set of bifilar windings on the first common mode choke and the second set of bifilar windings on the second common mode choke and ground; a third common mode choke having a first set of bifilar windings and a second set of bifilar windings where the first set of bifilar windings of the third common mode choke is connected in series with the first capacitive structure and the second set of bifilar windings of the third common mode choke is connected in series with the second capacitive structure; a radiofrequency shielded housing to contain the radiofrequency filter circuit; a cover plate to enclose the radiofrequency filter circuit in the radiofrequency shielded housing; an input connector electrically connected to the first input terminal and the second input terminal; and an output connector electrically connected to the first output terminal and the second output terminal. ### Claim 14 (depends on 13) The radiofrequency filter circuit of claim 13, wherein the input connector and the output connector are USB connectors. ### Claim 15 (depends on 13) The radiofrequency filter circuit of claim 13, further comprising an electromagnetically shielded test enclosure mechanically and electromagnetically coupled to the radiofrequency filter circuit. ### Claim 16 (depends on 13) The radiofrequency filter circuit of claim 13, further comprising a flange with a recess to surround the output connector. ### Claim 17 (depends on 16) The radiofrequency filter circuit of claim 16, wherein the flange has a plurality of threaded insets for receiving threaded fasteners. ### Claim 18 (depends on 13) The radiofrequency filter circuit of claim 13, wherein the radiofrequency shielded housing has a recess to retain the cover plate and provide a radiofrequency tight seal.