# US 10,120,406 B1 · Adaptive common mode dimmer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,120,406 B1 - Document ID: US10120406B1 - Status: Granted - Kind: B1 - Application number: 15/901,530 - Filed: 2018-02-21 - Published: 2018-11-01 - Granted: 2018-11-06 - Earliest claimed: 2017-04-27 - Assignees: Microchip Technology Incorporated - Applicants: Microchip Technology Incorporated - Inventors: Tony Susanto; Maarten Kuijk - Web page: https://patentgrep.com/patent/US10120406B1 ## CPC - G05F 3/262: {using field-effect transistors only} - H03K 17/162: {without feedback from the output circuit to the control circuit} - H03K 19/018564: {with at least one differential stage (H03K19/018578 takes precedence)} - H04B 1/58: Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa - H04B 3/28: Reducing interference caused by currents induced in cable sheathing or armouring - H04B 3/50: Systems for transmission between fixed stations via two-conductor transmission lines (H04B3/54 takes precedence) - H04L 7/0087: {Preprocessing of received signal for synchronisation, e.g. by code conversion, pulse generation or edge detection} - H04L 25/0276: {Arrangements for coupling common mode signals} - H04L 25/028: {Arrangements specific to the transmitter end} - H04L 25/085: {Arrangements for reducing interference in line transmission systems, e.g. by differential transmission} - G05F: SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract An adaptive mode has been added in a common mode (CM) dimmer circuit to increase output current capability only when needed. Without having an adaptive mode in the CM dimmer, the output current drivers must operate with large quiescent current to handle a bulk current injection (BCI) event. Therefore, a CM dimmer without the adaptive mode will consume a significant amount of power even when there is no BCI event occurring. With the adaptive mode, the CM dimmer can be used effectively to suppress the BCI event, e.g., in a transformer-less physical layer (PHY) connection, while consuming minimal power during normal circuit operation. ## Claims ### Claim 1 An adaptive common mode dimmer, comprising: a common mode dimmer having a low operating quiescent current first mode and a higher operating quiescent current second mode; and the common mode dimmer is adapted for coupling to a two-wire transmission line and maintaining a common mode voltage thereon at a desired common mode reference voltage, wherein the common mode dimmer comprises two comparators defining a reference voltage window and wherein the two-wire transmission line carries differential signals; wherein the common mode dimmer is in the first mode when the common mode voltage on the two-wire transmission line is within the reference voltage window between a high common mode reference voltage and a low common mode reference voltage, and is in the second mode otherwise. ### Claim 2 (depends on 1) The adaptive common mode dimmer according to claim 1, wherein: the high common mode reference voltage is less than a power supply voltage; the desired common mode reference voltage is less than the high common mode reference voltage; and the low common mode reference voltage is less than the desired common mode reference voltage and greater than a ground or power supply common. ### Claim 3 (depends on 2) The adaptive common mode dimmer according to claim 2, wherein the desired common mode reference voltage is about one-half of the power supply voltage. ### Claim 4 (depends on 1) The adaptive common mode dimmer according to claim 1, wherein a bulk current injection (BCI) event causes the common mode voltage to be above the high common mode reference voltage or below the low common mode reference voltage, wherein the common mode dimmer is in the second mode. ### Claim 5 (depends on 4) The adaptive common mode dimmer according to claim 4, wherein the BCI event causes at least 200 milliamperes of common mode current on the two-wire transmission line and the common mode dimmer is in the second mode when the common mode voltage is greater than the high common mode reference voltage or less than the low common mode reference voltage. ### Claim 6 (depends on 1) The adaptive common mode dimmer according to claim 1, wherein the common mode dimmer causes the common mode voltage to return to between the high and low common mode reference voltages before changing from the second mode to the first mode. ### Claim 7 (depends on 1) The adaptive common mode dimmer according to claim 1, wherein when the common mode voltage is above the desired common mode reference voltage the common mode dimmer sinks current from the two-wire transmission line to a ground or power supply common. ### Claim 8 (depends on 1) The adaptive common mode dimmer according to claim 1, wherein when the common mode voltage is below the desired common mode reference voltage the common mode dimmer sources current to the two-wire transmission line from the power supply voltage. ### Claim 9 A method for reducing common mode voltage on a differential signal transmission line by using an adaptive common mode dimmer having low and high operating quiescent current modes, said method comprising the steps of: providing a common mode dimmer having a low operating quiescent current first mode and a higher operating quiescent current second mode and comprising a first and second comparator defining a reference voltage window; coupling the common mode dimmer to a two-wire transmission line for maintaining a common mode voltage thereon at a desired common mode reference voltage, wherein the two-wire transmission line carries differential signals; operating the common mode dimmer in the first mode when the common mode voltage on the two-wire transmission line is within the reference voltage window between a high common mode reference voltage and a low common mode reference voltage; and operating the common mode dimmer in the second mode when the common mode voltage on the two-wire transmission line is greater than the high common mode reference voltage or lower than the low common mode reference voltage. ### Claim 10 (depends on 9) The method according to claim 9, wherein: the high common mode reference voltage is less than a power supply voltage; the desired common mode reference voltage is less than the high common mode reference voltage; and the low common mode reference voltage is less than the desired common mode reference voltage and greater than a ground or power supply common. ### Claim 11 (depends on 10) The method according to claim 10, wherein the desired common mode reference voltage is about one-half of the power supply voltage. ### Claim 12 (depends on 9) The method according to claim 9, comprises the step of causing the common mode dimmer to be in the second mode during a bulk current injection (BCI) event when the common mode voltage is above the high common mode reference voltage or below the low common mode reference voltage. ### Claim 13 (depends on 9) The method according to claim 9, comprises the step of returning the common mode voltage to between the high and low common mode reference voltages when the common mode dimmer is in the second mode. ### Claim 14 (depends on 9) The method according to claim 9, comprises the step of sinking current from the two-wire transmission line to ground or power supply common when the common mode voltage is above the desired common mode reference voltage. ### Claim 15 (depends on 9) The method according to claim 9, comprises the step of sourcing current to the two-wire transmission line from a power supply voltage when the common mode voltage is below the desired common mode reference voltage. ### Claim 16 A system for transmission of signals over a differential transmission line and having adaptive common mode dimmers with low and high operating quiescent current modes, said system comprising: a differential signal transmitter having a first adaptive common mode dimmer coupled thereto; a differential signal receiver having a second adaptive common mode dimmer coupled thereto; and a differential signal transmission line coupling the differential signal transmitter and the differential signal receiver; the first and second adaptive common mode dimmers each comprise two comparators defining a reference voltage window and each have a low operating quiescent current first mode and a higher operating quiescent current second mode; wherein the first and second adaptive common mode dimmers are in the first mode when a common mode voltage on the two-wire transmission line is within the reference voltage window between a high common mode reference voltage and a low common mode reference voltage, and are in the second mode otherwise. ### Claim 17 An adaptive common mode dimmer, comprising: a first set of current drivers coupled between a power supply voltage and a two-wire transmission line; a second set of current drivers coupled between a ground or power supply common and the two-wire transmission line; first and second voltage comparators having outputs coupled to and controlling the first and second sets of current drivers, respectively, first inputs coupled to the two-wire transmission line, and second inputs coupled to a first reference voltage, wherein the first reference voltage is less than the power supply voltage and greater than the ground or power supply common; wherein when a common mode voltage on the two-wire transmission line is greater than the first reference voltage the second set of current drivers will sink more current than the first set of current drivers will source, and when the common mode voltage on the two-wire transmission line is less than the first reference voltage the first set of current drivers will source more current than the second set of current drivers will sink; a third voltage comparator having a first input coupled to a second reference voltage, a second input coupled to the two-wire transmission line, and an output coupled to the second set of current drivers for increasing their operating quiescent current when the common mode voltage is greater than the second reference voltage, wherein the second reference voltage is greater than the first reference voltage; and a fourth voltage comparator having a first input coupled to a third reference voltage, a second input coupled to the two-wire transmission line, and an output coupled to the first set of current drivers for increasing their operating quiescent current when the common mode voltage is less than the third reference voltage, wherein the third reference voltage is less than the first reference voltage. ### Claim 18 (depends on 17) The adaptive common mode dimmer according to claim 17, wherein the first reference voltage is about one-half the power supply voltage. ### Claim 19 (depends on 17) The adaptive common mode dimmer according to claim 17, further comprising a first buffer transistor between the output of the fourth voltage comparator and the first set of current drivers. ### Claim 20 (depends on 17) The adaptive common mode dimmer according to claim 17, further comprising a second buffer transistor between the output of the third voltage comparator and the second set of current drivers.