# US 8,569,674 B2 · Multiplexed photocurrent monitoring circuit comprising current mirror circuits > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,569,674 B2 - Document ID: US8569674B2 - Status: Granted - Kind: B2 - Application number: 12/673,895 - Filed: 2007-08-21 - Published: 2011-05-05 - Granted: 2013-10-29 - Earliest claimed: 2007-08-21 - Assignees: Nippon Telegraph and Telephone Corporation; NTT Electronics Corporation - Applicants: Ryosuke Saito; Hisanobu Tanigawa; Takashi Goh; Ryoichi Kasahara - Inventors: Ryosuke Saito; Hisanobu Tanigawa; Takashi Goh; Ryoichi Kasahara - Web page: https://patentgrep.com/patent/US8569674B2 ## CPC - G01J 1/44: Electric circuits {(for command of an exposure part G03B7/02)} - H10F 30/21: the devices being sensitive to infrared, visible or ultraviolet radiation - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION ## Abstract A low cost photocurrent monitoring circuit is provided. A photocurrent monitoring circuit, which performs monitoring by converting photocurrents output from a plurality of photodiodes (PD1 to PDn) into voltage, includes: a multiplexer circuit (MUX) for selecting one of input terminals to establish a connection of the selected input terminal to an output terminal, wherein the photodiodes (PD1 to PDn) are respectively connected to the input terminals; and an amplifier (LA) for converting a photocurrent which flows from a selected photodiode via the multiplexer circuit (MUX) into a voltage, and for outputting the voltage. ## Claims ### Claim 1 A photocurrent monitoring circuit, which performs monitoring by converting photocurrents output from a plurality of photodiodes into voltages and by performing time division multiplexing for the obtained voltages, comprising: a plurality of current mirror circuits respectively connected to each photodiode, for receiving each photocurrent and supplying a photocurrent having the same value as that of the received photocurrent, each current mirror circuit comprising: a first current mirror configured to convert the photocurrent received from the photodiode into an intermediate photocurrent; and a second current mirror configured to convert the intermediate photocurrent into the photocurrent supplied by the current mirror circuit; a multiplexer circuit for selecting one of input terminals to establish a connection of the selected input terminal to an output terminal, wherein the current mirror circuits are respectively connected to the input terminals; and an amplifier for converting a photocurrent which flows from a selected current mirror circuit via the multiplexer circuit into a voltage, and for outputting the voltage, wherein the current mirror circuits are configured to sink current from the photodiodes and source current to the amplifier. ### Claim 2 (depends on 1) A photocurrent monitoring circuit according to claim 1, wherein the amplifier is a logarithmic amplifier, and converts a photocurrent emitted by the current mirror circuits into a voltage. ### Claim 3 (depends on 1) A photocurrent monitoring circuit according to claim 1, wherein the amplifier is a trans-impedance amplifier, and converts a photocurrent induced by the current mirror circuits into a voltage. ### Claim 4 (depends on 1) The photocurrent monitoring circuit recited in claim 1, wherein the current mirror circuits are connected to anodes of the photodiodes. ### Claim 5 A circuit for monitoring photocurrents output from a plurality of photodiodes and converting the photocurrents to a multiplexed voltage signal, the circuit comprising: a plurality of current mirror circuits, each current mirror circuit having an input and an output, each input being configured to respectively electrically connect to a separate one of the photodiodes, each current mirror circuit being configured to provide a photocurrent at the output having a same value as a photocurrent at the input, each current mirror circuit comprising: a first current mirror configured to convert the photocurrent received at the input into an intermediate photocurrent; and a second current mirror configured to convert the intermediate photocurrent into the photocurrent provided at the output; a multiplexer circuit having a plurality of input terminals and an output terminal, each of the input terminals being electrically connected to a separate one of the outputs of the current mirror circuits, the multiplexer circuit being configured to electrically connect each of the input terminals to the output terminal in a time division multiplexed manner so as to output the photocurrents of each of the outputs of the current mirrors, interleaved with each other; and an amplifier electrically connected to the output terminal of the multiplexer circuit, the amplifier being configured to convert the interleaved photocurrents into a multiplexed voltage signal, wherein the current mirror circuits are configured to sink current from the photodiodes and source current to the amplifier. ### Claim 6 (depends on 5) The circuit recited in claim 5, wherein the amplifier comprises a logarithmic amplifier configured to convert a photocurrent emitted by the current mirror circuits into a voltage. ### Claim 7 (depends on 5) The circuit recited in claim 5, wherein the amplifier comprises a trans-impedance amplifier configured to convert a photocurrent induced by the current mirror circuits into a voltage. ### Claim 8 (depends on 5) The circuit recited in claim 5, wherein the output of each current mirror circuit has a low impedance so as to be unaffected by load fluctuations at the input terminals of the multiplexer circuit. ### Claim 9 (depends on 5) The circuit recited in claim 5, wherein the input of each current mirror circuit is configured to respectively electrically connect to an anode of one of the photodiodes. ### Claim 10 A circuit for monitoring photocurrents output from a plurality of photodiodes and converting the photocurrents to a multiplexed voltage signal, the circuit comprising: a plurality of current mirror circuits, each current mirror circuit having an input and an output, each input being configured to respectively electrically connect to a separate one of the photodiodes, each current mirror circuit being configured to provide a photocurrent at the output having a same value as a photocurrent at the input, each current mirror circuit comprising two or more pairs of transistors, bases of the transistors in each pair being electrically connected together; a multiplexer circuit having a plurality of input terminals and an output terminal, each of the input terminals being electrically connected to a separate one of the outputs of the current mirror circuits, the multiplexer circuit being configured to electrically connect each of the input terminals to the output terminal in a time division multiplexed manner so as to output the photocurrents of each of the outputs of the current mirrors, interleaved with each other; and an amplifier electrically connected to the output terminal of the multiplexer circuit, the amplifier being configured to convert the interleaved photocurrents into a multiplexed voltage signal. ### Claim 11 (depends on 10) The circuit recited in claim 10, wherein the amplifier comprises a logarithmic amplifier configured to convert a photocurrent emitted by the current mirror circuits into a voltage. ### Claim 12 (depends on 10) The circuit recited in claim 10, wherein the amplifier comprises a trans-impedance amplifier configured to convert a photocurrent induced by the current mirror circuits into a voltage. ### Claim 13 (depends on 10) The photocurrent monitoring circuit recited in claim 10, wherein the input of each current mirror circuit is configured to respectively electrically connect to an anode of one of the photodiodes.