# US 8,786,321 B2 · Power harvesting in open drain transmitters > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,786,321 B2 - Document ID: US8786321B2 - Status: Granted - Kind: B2 - Application number: 12/982,583 - Filed: 2010-12-30 - Published: 2012-07-05 - Granted: 2014-07-22 - Earliest claimed: 2010-12-30 - Assignees: STMicroelectronics International N.V. - Applicants: Nitin Gupta; Tapas Nandy - Inventors: Nitin Gupta; Tapas Nandy - Web page: https://patentgrep.com/patent/US8786321B2 ## CPC - H04L 25/0272: {Arrangements for coupling to multiple lines, e.g. for differential transmission} - G09G 2330/023: using energy recovery or conservation - G09G 2370/12: Use of DVI or HDMI protocol in interfaces along the display data pipeline - H04N 21/43635: {HDMI} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00) - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract A transmitter having at least one channel comprising a first differential circuit driven by a differential data signal, the first differential circuit configured to output the differential data at a first and second output and a first control circuit coupled between the first differential circuit and the first and second output, the first control circuit driven by a drive voltage. ## Claims ### Claim 1 A transmitter comprising: a channel including: a differential output line; a first differential circuit including: a differential input configured to receive a differential input signal, and a differential output coupled to the differential output line of the channel; and a first control circuit coupled between the differential output of the first differential circuit and the differential output line of the channel, the first control circuit having an input configured to receive a first control signal, wherein the first differential circuit includes a p-channel MOSFET, wherein the differential output line is configured to couple to a receiver, wherein the first differential circuit is configured to draw current from the receiver, wherein a voltage of the first control signal is less than or equal to a voltage of a power supply signal recovered from the current drawn from the receiver plus a threshold voltage of an n-channel MOSFET plus a threshold voltage of a p-channel MOSFET, wherein the first control signal is provided by a control signal generating circuit having one or more components supplied by a power supply voltage recovered from a drive signal provided at a terminal of the first differential circuit, wherein: the transmitter further comprises the control signal generating circuit; the control signal generating circuit includes: a second differential circuit driven by the differential input signal; and a voltage controller for controlling a voltage of the first control signal in response to a voltage control signal. ### Claim 2 (depends on 1) The transmitter of claim 1, further comprising: a voltage generation circuit coupled to the first differential circuit and configured to generate the power supply voltage from the drive signal. ### Claim 3 (depends on 2) The transmitter of claim 2, further comprising: first and second amplifier circuits configured to amplify the differential input signal. ### Claim 4 (depends on 3) The transmitter of claim 3, wherein the first and second amplifiers are powered by the power supply voltage. ### Claim 5 (depends on 1) The transmitter of claim 1, wherein the first differential circuit comprises a first differential transistor pair, which includes the p-channel MOSFET of the first differential circuit. ### Claim 6 (depends on 1) The transmitter of claim 1, wherein the differential output of the first differential circuit comprises an open drain output. ### Claim 7 (depends on 1) The transmitter of claim 1, wherein the first control circuit comprises a cascode transistor pair. ### Claim 8 (depends on 2) The transmitter of claim 2, wherein the voltage generation circuit comprises a voltage regulator. ### Claim 9 (depends on 8) The transmitter of claim 8 wherein the voltage regulator comprises: a shunt regulator coupled to a capacitor. ### Claim 10 (depends on 1) The transmitter of claim 1, wherein the voltage controller is configured to receive a second drive signal provided at a terminal of the second differential circuit. ### Claim 11 (depends on 10) The transmitter of claim 10, wherein the second differential circuit comprises a differential transistor pair. ### Claim 12 (depends on 11) The transmitter of claim 11, further comprising: biasing circuitry configured to bias the second differential circuit such that a current of the second drive signal provided at the terminal of the second differential circuit is at least an order of magnitude less than a current of the drive signal provided at the terminal of the first differential circuit. ### Claim 13 (depends on 10) The transmitter of claim 10, wherein the terminal of the second differential circuit is coupled to an external resistor, and the second drive signal generates a voltage across the external resistor. ### Claim 14 (depends on 13) The transmitter of claim 13, wherein the voltage across the external resistor is equal to the power supply voltage when the voltage of the first control signal corresponds to a predetermined value. ### Claim 15 (depends on 14) The transmitter of claim 14, wherein: the first control circuit comprises a cascode transistor pair. ### Claim 16 (depends on 13) The transmitter of claim 13, wherein the control signal generating circuit further comprises: a comparator configured to generate the voltage control signal based on a comparison between the power supply voltage and the voltage across the external resistor. ### Claim 17 (depends on 1) The transmitter of claim 1, wherein the voltage controller comprises: a control transistor with a gate configured to receive the voltage control signal and a drain configured to receive the first control signal and a source coupled to ground. ### Claim 18 (depends on 1) The transmitter of claim 1, wherein the transmitter is a HDMI transmitter. ### Claim 19 (depends on 18) The transmitter of claim 18, wherein the transmitter further comprises second, third, and fourth channels. ### Claim 20 (depends on 19) The transmitter of claim 19, wherein the channel, the second channel, the third channel, and/or the fourth channel is a clock channel. ### Claim 21 A circuit board comprising: a transmitter having a channel and a voltage regulator, wherein the channel includes: a first differential circuit including: a differential input configured to receive a differential input signal, and a differential output coupled to a differential output terminal of the channel; and a first control circuit coupled between the differential output of the first differential circuit and the differential output terminal of the channel, the first control circuit having an input configured to receive a control signal, wherein the voltage regulator is configured to regulate a voltage of a power supply signal recovered from a current drawn by the transmitter from a receiver coupled to the channel, wherein the voltage of the power supply signal recovered from the current drawn from the receiver is less than a voltage at a node coupled between the first control circuit and the differential output of the first differential circuit, and wherein a voltage of the control signal is less than or equal to the voltage of the power supply signal recovered from the current drawn from the receiver plus a threshold voltage of an n-channel MOSFET plus a threshold voltage of a p-channel MOSFET. ### Claim 22 A system comprising: a high-definition multimedia interface (HDMI) receiver; and an HDMI transmitter configured to transmit data to the HDMI receiver, the HDMI transmitter having a channel and a voltage regulator, wherein the channel includes: a first differential circuit including: a differential input configured to receive a differential input signal, and a differential output coupled to a differential output terminal of the channel, and a first control circuit coupled between the differential output of the first differential circuit and the differential output terminal of the channel, the first control circuit having an input configured to receive a control signal, wherein the voltage regulator is configured to regulate a voltage of a power supply signal recovered from a current drawn by the HDMI transmitter from the HDMI receiver, wherein the voltage of the power supply signal recovered from the current drawn from the HDMI receiver is less than a voltage at a node coupled between the first control circuit and the differential output of the first differential circuit, and wherein a voltage of the control signal is less than or equal to the voltage of the power supply signal recovered from the current drawn from the HDMI receiver plus a threshold voltage of an n-channel MOSFET plus a threshold voltage of a p-channel MOSFET. ### Claim 23 (depends on 21) The circuit board of claim 21, wherein the first differential circuit includes a p-channel MOSFET. ### Claim 24 (depends on 22) The system of claim 22, wherein the first differential circuit includes a p-channel MOSFET. ### Claim 25 (depends on 21) The circuit board of claim 21, wherein the transmitter further includes a control signal generating circuit configured to provide the control signal, and wherein the control signal generating circuit includes one or more components supplied by the power supply signal recovered from the current drawn from the receiver. ### Claim 26 (depends on 22) The system of claim 22, wherein the HDMI transmitter further includes a control signal generating circuit configured to provide the control signal, and wherein the control signal generating circuit includes one or more components supplied by the power supply signal recovered from the current drawn from the receiver.