# US 11,309,839 B2 · High signal-to-noise ratio amplifier with multiple output modes > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,309,839 B2 - Document ID: US11309839B2 - Status: Granted - Kind: B2 - Application number: 16/793,226 - Filed: 2020-02-18 - Published: 2020-11-12 - Granted: 2022-04-19 - Earliest claimed: 2019-05-06 - Assignees: Mediatek Inc. - Applicants: Mediatek Inc. - Inventors: Sung-Han Wen; Kuan-Ta Chen - Web page: https://patentgrep.com/patent/US11309839B2 ## CPC - H03F 1/02: Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation - H03F 3/72: Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal - H03F 1/08: Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements (wide-band amplifiers with inter-stage coupling networks incorporating these impedances H03F1/42) - H03F 1/26: Modifications of amplifiers to reduce influence of noise generated by amplifying elements - H03F 1/3247: {using feedback acting on predistortion circuits (H03F1/3264 takes precedence)} - H03F 1/34: Negative-feedback-circuit arrangements with or without positive feedback (H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence {; for rejection of common mode signals H03F3/45479}) - H03F 3/04: with semiconductor devices only - H03F 3/181: Low-frequency amplifiers, e.g. audio preamplifiers - H03F 3/211: {using a combination of several amplifiers (H03F3/60 takes precedence)} - H03G 3/30: in amplifiers having semiconductor devices - H03F 2200/03: the amplifier being designed for audio applications - H03F 2200/153: Feedback used to stabilise the amplifier - H03F 2200/156: One or more switches are realised in the feedback circuit of the amplifier stage - H03F 2200/372: Noise reduction and elimination in amplifier - H03F 2200/405: the output amplifying stage of an amplifier comprising more than three power stages - H03F 2200/408: the output amplifying stage of an amplifier comprising three power stages - H03F 2203/7233: the gated amplifier, switched on or off by putting into parallel or not, by choosing between amplifiers by one or more switch(es), being impedance adapted by switching an adapted passive network - H03F 2203/7236: the gated amplifier being switched on or off by putting into parallel or not, by choosing between amplifiers by (a ) switch(es) - H03F 2203/7239: the gated amplifier being switched on or off by putting into parallel or not, by choosing between amplifiers and shunting lines by one or more switch(es) - H03G 2201/103: being an amplifying element - H03F: AMPLIFIERS - H03G: CONTROL OF AMPLIFICATION ## Abstract A multi-stage amplifier with a high signal-to-noise ratio is introduced. Multiple amplification stages are cascaded between an input terminal and an output terminal of the amplifier. A controller switches the output stage among the multiple amplification stages from a normal mode to an attenuation mode in response to the amplifier input being lower than the threshold. In the attenuation mode, the output stage provides an attenuation resistor coupled in series with the load resistor of the amplifier. Noise is successfully attenuated by the attenuation-mode output stage. ## Claims ### Claim 1 An amplifier, comprising: a plurality of amplification stages, cascaded between an input terminal and an output terminal of the amplifier, wherein an output stage among the plurality of amplification stages is switched between a normal mode and an attenuation mode; a controller, operable to switch the output stage from the normal mode to the attenuation mode in response to an amplifier input signal at the input terminal being lower than a threshold; a first feedback resistor and a first switch, connected in series; and a second feedback resistor and a second switch, connected in series; wherein: when the output stage is in the normal mode, the first switch is closed and the second switch is open, and the output terminal of the amplifier is coupled to an input stage among the plurality of amplification stages via the first feedback resistor; and when the output stage is in the attenuation mode, the second switch is closed and the first switch is open, the output stage provides an attenuation resistor coupled in series with a load resistor of the amplifier, a first terminal of the attenuation resistor is coupled to the input stage via the second feedback resistor and a second terminal of the attenuation resistor is coupled to the load resistor. ### Claim 2 (depends on 1) The amplifier as claimed in claim 1, wherein: the controller is operable to switch the output stage from the normal mode to the attenuation mode at zero-crossing points of an output signal of the amplifier. ### Claim 3 (depends on 1) The amplifier as claimed in claim 1, wherein: the amplifier is operable to receive the amplifier input signal, and a digital signal from a digital analog front-end circuit is converted to an analog form as the amplifier input signal to be amplified by the amplifier. ### Claim 4 (depends on 3) The amplifier as claimed in claim 3, wherein: the controller controls the digital analog front-end circuit to digitally compensate for signal attenuation due to the attenuation resistor. ### Claim 5 (depends on 4) The amplifier as claimed in claim 4, wherein: the digital analog front-end circuit uses a digital gain to digitally compensate for signal attenuation due to the attenuation resistor. ### Claim 6 (depends on 5) The amplifier as claimed in claim 5, wherein: when operating the output stage in the attenuation mode, the controller increases resistance of the attenuation resistor step-by-step. ### Claim 7 (depends on 6) The amplifier as claimed in claim 6, wherein: when increasing the resistance of the attenuation resistor step-by-step, the controller increases the digital gain accordingly. ### Claim 8 (depends on 1) The amplifier as claimed in claim 1, further comprising: a feedback circuit comprising the first feedback resistor, the first switch, the second feedback resistor, and the second switch, coupling a feedback signal of an output signal of the amplifier to an input stage among the plurality of amplification stages, wherein the controller controls the feedback circuit to compensate for signal attenuation due to the attenuation resistor. ### Claim 9 (depends on 8) The amplifier as claimed in claim 8, wherein: the controller controls resistance of the feedback circuit to use an analog gain to compensate for signal attenuation due to the attenuation resistor. ### Claim 10 (depends on 9) The amplifier as claimed in claim 9, wherein: when operating the output stage in the attenuation mode, the controller increases resistance of the attenuation resistor step-by-step. ### Claim 11 (depends on 10) The amplifier as claimed in claim 10, wherein: when increasing the resistance of the attenuation resistor step-by-step, the controller increases the resistance of the feedback circuit accordingly. ### Claim 12 (depends on 1) The amplifier as claimed in claim 1, wherein: the controller switches the output stage from the attenuation mode to the normal mode in response to the amplifier input signal reaching the threshold. ### Claim 13 (depends on 12) The amplifier as claimed in claim 12, wherein: the controller switches the output stage between the normal mode and the attenuation mode at zero-crossing points of an output signal of the amplifier. ### Claim 14 (depends on 1) The amplifier as claimed in claim 1, wherein: resistance of the attenuation resistor is greater than resistance of the load resistor. ### Claim 15 (depends on 1) The amplifier as claimed in claim 1, wherein: the output stage further includes a first operational amplifier enabled in the normal mode and disabled in the attenuation mode and a second operational amplifier disabled in the normal mode and enabled in the attenuation mode; when the output stage is in the normal mode, a second-to-last amplification stage is coupled to the output terminal of the amplifier through the first operational amplifier; and when the output stage is in the attenuation mode, the second-to-last amplification stage is coupled to the output terminal of the amplifier through the second operational amplifier and the attenuation resistor. ### Claim 16 (depends on 1) The amplifier as claimed in claim 1, wherein: resistance of the attenuation resistor is greater than resistance of the load resistor; and resistance of the second feedback resistor is greater than the first feedback resistor. ### Claim 17 (depends on 1) The amplifier as claimed in claim 1, wherein: resistance of the attenuation resistor is k times the load resistor; resistance of the second feedback resistor is k times the first feedback resistor; and k is a number greater than 1.