# US 2013/0278342 A1 · Broadband Transconductance Amplifier > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0278342 A1 - Document ID: US20130278342A1 - Status: Published application - Kind: A1 - Application number: 13/450,570 - Filed: 2012-04-19 - Published: 2013-10-24 - Earliest claimed: 2012-04-19 - Assignees: Fujitsu Semiconductor Limited - Inventors: Dong-Jun Yang; Mohammed Shah Alam - Web page: https://patentgrep.com/patent/US20130278342A1 ## CPC - H03F 3/195: in integrated circuits - H03F 3/193: with field-effect devices (H03F3/195 takes precedence) - H03G 1/0094: {using switched capacitors} - H03F: AMPLIFIERS - H03G: CONTROL OF AMPLIFICATION ## Abstract A transconductance amplifier having an input terminal for receiving an input signal and an output terminal for communicating an output signal based on the input signal, the transconductance amplifier may include a gain transistor and a variable capacitance. The gain transistor may have a gate terminal, a first non-gate terminal, and a second non-gate terminal, the first non-gate terminal coupled to the output terminal of the transconductance amplifier. The variable capacitance may be coupled between the gate terminal of the gain transistor and the second non-gate terminal of the gain transistor. ## Claims ### Claim 1 A transconductance amplifier having an input terminal for receiving an input signal and an output terminal for communicating an output signal based on the input signal, the transconductance amplifier comprising: a gain transistor having a gate terminal, a first non-gate terminal, and a second non-gate terminal, the first non-gate terminal coupled to the output terminal of the transconductance amplifier; and a variable capacitance coupled between the gate terminal of the gain transistor and the second non-gate terminal of the gain transistor. ### Claim 2 (depends on 1) The transcondcutance amplifier of claim 1, the variable capacitance comprising: a non-switched capacitor coupled between the gate terminal of the gain transistor and the second non-gate terminal of the gain transistor; a switched capacitor having a first terminal and a second terminal; and a switching transistor having a gate terminal, a first non-gate terminal, and a second non-gate terminal, the first non-gate terminal coupled to the first terminal of the switched capacitor, and the gate terminal of the switching transistor coupled to a control terminal of the transconductance amplifier for receiving a control signal; wherein one of the second terminal of the switched capacitor and the second non-gate terminal of the switching transistor is coupled to the gate terminal of the gain transistor and the other of the second terminal of the switched capacitor and the second non-gate terminal of the switching transistor is coupled to the second-non gate terminal of the gain transistor. ### Claim 3 (depends on 2) The transconductance amplifier of claim 2, the gate of the switching transistor coupled to the control terminal via a resistive-capacitive circuit comprising a control input resistor and a control input capacitor. ### Claim 4 (depends on 3) The transconductance amplifier of claim 3, wherein: the control input resistor is coupled between the control terminal and the gate terminal of the switching transistor; and the control input resistor having a first terminal and a second terminal, the control input resistor coupled at its first terminal to the gate terminal of the switching transistor and configured to be coupled at its second terminal to a supply potential. ### Claim 5 (depends on 1) The transconductance amplifier of claim 1, the variable capacitance being based on an operating frequency of the transconductance amplifier. ### Claim 6 (depends on 1) The transcondcutance amplifier of claim 1, the gain transistor comprising an n-type metal-oxide-semiconductor field-effect transistor. ### Claim 7 (depends on 1) The transconductance amplifier of claim 1, wherein the first non-gate terminal of the gain transistor is coupled to the output terminal of the transconductance amplifier via another transistor. ### Claim 8 (depends on 1) The transconductance amplifier of claim 1, further comprising an inductor having a first terminal and a second terminal, the inductor coupled at its first terminal to the second non-gate terminal of the switching transistor and configured to be coupled at its second terminal to a supply potential. ### Claim 9 (depends on 1) The transconductance amplifier of claim 1, the variable capacitance comprising: a non-switched capacitor coupled between the gate terminal of the gain transistor and the second non-gate terminal of the gain transistor; a plurality of switched capacitors, each switched capacitor having a first terminal and a second terminal; and a plurality of switching transistors, each switching transistor having a gate terminal, a first non-gate terminal, and a second non-gate terminal, each particular first non-gate terminal coupled to the first terminal of an associated switched capacitor of the plurality of switched capacitors, and the gate terminal of the particular switching transistor coupled to a control terminal of the transconductance amplifier for receiving a control signal; wherein one of the second terminal of the associated switched capacitor and the second non-gate terminal of the particular switching transistor is coupled to the gate terminal of the gain transistor and the other of the second terminal of the associated switched capacitor and the second non-gate terminal of the particular switching transistor is coupled to the second-non gate terminal of the gain transistor. ### Claim 10 A wireless communication element, comprising: a transmit path configured to convert a first digital signal into a first modulated wireless communication signal and transmit the first modulated wireless communication signal; and a receive path configured to receive a second modulated wireless communication signal and convert the second wireless communication signal into a second digital signal, the receive path comprising a transconductance amplifier having an input terminal for receiving an input signal and an output terminal for communicating an output signal based on the input signal, the transconductance amplifier comprising: a gain transistor having a gate terminal, a first non-gate terminal, and a second non-gate terminal, the first non-gate terminal coupled to the output terminal of the transconductance amplifier; and a variable capacitance coupled between the gate terminal of the gain transistor and the second non-gate terminal of the gain transistor. ### Claim 11 (depends on 10) The wireless communication element of claim 10, the variable capacitance comprising: a non-switched capacitor coupled between the gate terminal of the gain transistor and the second non-gate terminal of the gain transistor; a switched capacitor having a first terminal and a second terminal; and a switching transistor having a gate terminal, a first non-gate terminal, and a second non-gate terminal, the first non-gate terminal coupled to the first terminal of the switched capacitor, and the gate terminal of the switching transistor coupled to a control terminal of the transconductance amplifier for receiving a control signal; wherein one of the second terminal of the switched capacitor and the second non-gate terminal of the switching transistor is coupled to the gate terminal of the gain transistor and the other of the second terminal of the switched capacitor and the second non-gate terminal of the switching transistor is coupled to the second-non gate terminal of the gain transistor. ### Claim 12 (depends on 11) The wireless communication element of claim 11, the gate of the switching transistor coupled to the control terminal via a resistive-capacitive circuit comprising a control input resistor and a control input capacitor. ### Claim 13 (depends on 12) The wireless communication element of claim 12, wherein: the control input resistor is coupled between the control terminal and the gate terminal of the switching transistor; and the control input resistor having a first terminal and a second terminal, the control input resistor coupled at its first terminal to the gate terminal of the switching transistor and configured to be coupled at its second terminal to a supply potential. ### Claim 14 (depends on 10) The wireless communication element of claim 10, the variable capacitance based on an operating frequency of the transconductance amplifier. ### Claim 15 (depends on 10) The wireless communication element of claim 10, wherein the first non-gate terminal of the gain transistor is coupled to the output terminal of the transconductance amplifier via another transistor. ### Claim 16 (depends on 10) The wireless communication element of claim 10, the transconductance amplifier further comprising an inductor having a first terminal and a second terminal, the inductor coupled at its first terminal to the second non-gate terminal of the switching transistor and configured to be coupled at its second terminal to a supply potential. ### Claim 17 (depends on 10) The wireless communication element of claim 10, the variable capacitance comprising: a non-switched capacitor coupled between the gate terminal of the gain transistor and the second non-gate terminal of the gain transistor; a plurality of switched capacitors, each switched capacitor having a first terminal and a second terminal; and a plurality of switching transistors, each switching transistor having a gate terminal, a first non-gate terminal, and a second non-gate terminal, each particular first non-gate terminal coupled to the first terminal of an associated switched capacitor of the plurality of switched capacitors, and the gate terminal of the particular switching transistor coupled to a control terminal of the transconductance amplifier for receiving a control signal; wherein one of the second terminal of the associated switched capacitor and the second non-gate terminal of the particular switching transistor is coupled to the gate terminal of the gain transistor and the other of the second terminal of the associated switched capacitor and the second non-gate terminal of the particular switching transistor is coupled to the second-non gate terminal of the gain transistor. ### Claim 18 A method comprising: determining an operating frequency of a transconductance amplifier comprising: a gain transistor having a gate terminal coupled to an input terminal of the transconductance amplifier, a first non-gate terminal, and a second non-gate terminal; and a variable capacitance coupled between the gate terminal of the gain transistor and the first non-gate terminal of the gain transistor; and selecting a capacitance of the variable capacitance based on the operating frequency such that at least one of a magnitude of the input impedance of the input terminal of the transconductance amplifier and a quality factor associated with the input impedance remains substantially constant over a plurality of operating frequencies of the transconductance amplifier. ### Claim 19 (depends on 18) A method according to claim 18, wherein: the variable capacitance comprises: a switched capacitor having a first terminal and a second terminal; and a switching transistor having a gate terminal, a first non-gate terminal, and a second non-gate terminal, the first non-gate terminal coupled to the first terminal of the switched capacitor, and the gate terminal of the switching transistor coupled to a control terminal of the transconductance amplifier for receiving a control signal; wherein one of the second terminal of the switched capacitor and the second non-gate terminal of the switching transistor is coupled to the gate terminal of the gain transistor and the other of the second terminal of the switched capacitor and the second non-gate terminal of the switching transistor is coupled to the first-non gate terminal of the gain transistor and selecting the capacitance of the variable capacitance comprises selectively enabling or disabling the switched capacitor based on the operating frequency. ### Claim 20 (depends on 19) A method according to claim 19, wherein selecting the capacitance of the variable capacitance comprises generating the control signal based on the operating frequency.