# US 2010/0166227 A1 · Circuits for biasing/charging high impedance loads > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2010/0166227 A1 - Document ID: US20100166227A1 - Status: Published application - Kind: A1 - Application number: 12/649,965 - Filed: 2009-12-30 - Published: 2010-07-01 - Earliest claimed: 2008-12-30 - Inventors: John Laurence Pennock - Web page: https://patentgrep.com/patent/US20100166227A1 ## CPC - H04R 19/005: {using semiconductor materials} - H04R 19/016: {for microphones} - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract A charging circuit for charging/biasing high impedance loads such as capacitive loads. The circuit comprises an input for connecting to a voltage/charge source and an output for connecting to the load. A capacitor is connected between the output and a reference voltage such as ground and a reverse bias diode is connected between the input and the output terminals. The reverse bias diode is arranged to allow a reverse current to pass which is sufficient to compensate for current leakage at the output terminal or other parts of the circuit. The reverse bias diode is conveniently a polysilicon diode. The diode may be connected in parallel with a shunt device to allow for rapid charging during start up. ## Claims ### Claim 1 A circuit for charging a high impedance load, the circuit comprising: an input terminal; an output terminal; a capacitor electrically connected between the output terminal and a reference voltage; a charging reverse bias diode electrically connected between the input terminal and the output terminal; and a shunt device connected across said reverse bias diode. ### Claim 2 (depends on 1) A circuit as claimed in claim 1 wherein said reverse bias diode can allow a reverse current, under normal charged conditions, which is sufficient to compensate for current leakage at the output terminal. ### Claim 3 (depends on 1) A circuit according to claim 1 wherein the diode can allow a reverse current of up to 100 pA, or up to 10 pA or up to 1 pA. ### Claim 4 (depends on 1) A circuit according to claim 1 wherein the diode has a saturation current in the range of 10 fA to 100 pA. ### Claim 5 (depends on 4) A circuit as claimed in claim 4 wherein the saturation current is in the range 0.2-5 pA. ### Claim 6 (depends on 1) A circuit as claimed in claim 1 wherein said reverse bias diode comprises a polysilicon diode. ### Claim 7 (depends on 1) A circuit as claimed in claim 1 wherein said reverse bias diode comprises a p-i-n diode. ### Claim 8 (depends on 1) A circuit as claimed in claim 1 wherein said reverse bias diode comprises a multiple junction composite diode. ### Claim 9 (depends on 1) A circuit as claimed in claim 1 further comprising at least one additional reverse bias diode electrically connected between the input terminal and the output terminal. ### Claim 10 (depends on 1) A circuit as claimed in claim 1 wherein said shunt device is configured to pass current when the voltage level on the output terminal is below a threshold level and to pass substantially no current when the voltage level on the output terminal is above a threshold level. ### Claim 11 (depends on 10) A circuit as claimed in claim 10 wherein the threshold level is substantially the operating voltage of the high impedance load. ### Claim 12 (depends on 11) A circuit as claimed in claim 11 wherein the threshold level is within about 1V of the operating voltage of the high impedance load. ### Claim 13 (depends on 10) A circuit as claimed in claim 10 wherein the shunt device is configured to pass a current which is larger than the reverse current of the reverse bias diode when the voltage level on the output terminal is lower than the threshold level. ### Claim 14 (depends on 1) A circuit as claimed in claim 1 wherein the shunt device comprises at least one transistor element connected in parallel with the reverse bias diode. ### Claim 15 (depends on 14) A circuit as claimed in claim 14 wherein said transistor element is arranged as a forward diode connected transistor. ### Claim 16 (depends on 14) A circuit as claimed in claim 14 wherein the shunt device comprises at least two serially connected transistor elements connected in parallel with the reverse bias diode. ### Claim 17 (depends on 1) A circuit as claimed in claim 1 wherein the shunt device comprises at least one forward biased diode connected in parallel with the reverse bias diode. ### Claim 18 (depends on 1) A circuit as claimed in claim 1 further comprising a voltage bias device electrically connected to the input terminal. ### Claim 19 (depends on 18) A circuit as claimed in claim 18 wherein the voltage bias device comprises a charge pump. ### Claim 20 (depends on 18) A circuit as claimed in claim 18 comprising a capacitive transducer electrically connected to said output terminal. ### Claim 21 (depends on 20) A circuit as claimed in claim 20 wherein the capacitive transducer comprises a MEMS transducer having a first capacitive plate and a second capacitive plate and said first capacitive plate is electrically connected to said output terminal. ### Claim 22 (depends on 21) A circuit as claimed in claim 21 wherein the MEMS transducer comprises a MEMS microphone. ### Claim 23 (depends on 20) A circuit as claimed in claims 20 further comprising at least one of: an amplifier device electrically connected to said transducer arranged to amplify the electrical signals generated by said transducer; and an analogue to digital convertor device configured to convert electrical signals generated by said transducer into digital electrical signals. ### Claim 24 (depends on 1) A device comprising the circuit of claim 1 wherein said device is at least one of: a MEMS device; an ultrasound imager; a sonar transmitter; a sonar receiver; a mobile phone; a personal desktop assistant; an MP3 player or other audio player; and a laptop. ### Claim 25 A method of charging and/or biasing a high impedance load comprising the steps of: arranging a reverse bias diode between a voltage bias source and said capacitive load; arranging a capacitor between said high impedance load and a reference voltage such that at least some charging current passes through the reverse bias diode; and arranging a shunt device across the reverse bias diode, said shunt device being configured to pass current when the voltage level on the output terminal is below a threshold level and to pass substantially no current when the voltage level on the output terminal is above a threshold level. ### Claim 26 (depends on 25) A method as claimed in claim 25 comprising allowing a reverse current to pass through said reverse bias diode, under normal charged conditions, which is sufficient to compensate for current leakage. ### Claim 27 (depends on 26) A method as claimed in claim 26 wherein said reverse bias diode can allow a reverse current of up to 100 pA, or up to 10 pA or up to 1 pA. ### Claim 28 (depends on 25) A method as claimed in claim 25 wherein said reverse bias diode comprises a polysilicon diode. ### Claim 29 (depends on 25) A method as claimed in claim 25 wherein, during a start up phase, the method involves passing a charging current through the shunt device and, during an operative phase, involves passing a charging current through the reverse bias diode sufficient to compensate for any current leakage, wherein the charging current that can be passed through the shunt device is greater than the charging current that can be passed through the reverse bias diode. ### Claim 30 (depends on 25) A method as claimed in claim 25 wherein said shunt device comprises at least one transistor element. ### Claim 31 (depends on 25) A method as claimed in claim 25 wherein said shunt device comprises at least one forward biased diode connected in parallel with the reverse bias diode. ### Claim 32 A charging circuit for charging a high impedance load, the circuit comprising: an input terminal connected to a voltage bias source; an output terminal connected to said high impedance load; a capacitor electrically connected between the output terminal and a reference voltage; and a charging reverse bias diode electrically connected between the input terminal and the output terminal.