# US 11,444,576 B2 · Power amplifier bias modulation for multi-level supply envelope tracking > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,444,576 B2 - Document ID: US11444576B2 - Status: Granted - Kind: B2 - Application number: 16/948,548 - Filed: 2020-09-23 - Published: 2021-04-01 - Granted: 2022-09-13 - Earliest claimed: 2019-09-27 - Assignees: Skyworks Solutions, Inc. - Applicants: Skyworks Solutions, Inc. - Inventors: Serge Francois Drogi; Philip John Lehtola; Florinel G. Balteanu - Web page: https://patentgrep.com/patent/US11444576B2 ## CPC - H03F 1/0216: {Continuous control} - H03F 1/0227: {using supply converters} - H03F 1/0266: {by using a signal derived from the input signal} - H03F 1/22: by use of cascode coupling, i.e. earthed cathode or emitter stage followed by earthed grid or base stage respectively - H03F 3/195: in integrated circuits - H03F 3/245: {with semiconductor devices only} - H04B 1/0475: {with means for limiting noise, interference or distortion (H04B1/0483 takes precedence)} - H04B 1/16: Circuits - H04B 1/40: Circuits - H03F 2200/102: A non-specified detector of a signal envelope being used in an amplifying circuit - H03F 2200/105: A non-specified detector of the power of a signal being used in an amplifying circuit - H03F 2200/165: A filter circuit coupled to the input of an amplifier - H03F 2200/168: Two amplifying stages are coupled by means of a filter circuit - H03F 2200/18: the bias of the gate of a FET being controlled by a control signal - H03F 2200/306: the loading circuit of an amplifying stage being a parallel resonance circuit - H03F 2200/336: A I/Q, i.e. phase quadrature, modulator or demodulator being used in an amplifying circuit - H03F 2200/411: the output amplifying stage of an amplifier comprising two power stages - H03F 2200/451: the amplifier being a radio frequency amplifier - H04B 2001/0408: {with power amplifiers} - H03F: AMPLIFIERS - H04B: TRANSMISSION ## Abstract Apparatus and methods for power amplifier bias modulation for multi-level supply envelope tracking are provided herein. In certain embodiments, an envelope tracking system includes a power amplifier that amplifies a radio frequency signal, a multi-level supply envelope tracker that generates a power amplifier supply voltage of the power amplifier based on an envelope signal indicating an envelope of the radio frequency signal, and a bias modulation circuit that modulates a bias of the power amplifier based on a voltage level of the power amplifier supply voltage. ## Claims ### Claim 1 A mobile device comprising: a transceiver configured to generate a radio frequency signal; a front end circuit including a power amplifier configured to receive the radio frequency signal at a signal input and to provide an amplified radio frequency signal at a signal output, the power amplifier including an amplifier transistor configured to receive the radio frequency signal at a base, and a cascode transistor having an emitter connected to a collector of the amplifier transistor and a collector connected to the signal output; and a power management circuit including a multi-level supply envelope tracker configured to generate a power amplifier supply voltage of the power amplifier based on an envelope signal indicating an envelope of the radio frequency signal, a programmable supply voltage filter operable to filter the power amplifier supply voltage to generate a filtered power amplifier supply voltage, and a bias modulation circuit configured to modulate a bias of a base of the cascode transistor of the power amplifier based on a voltage level of the filtered power amplifier supply voltage. ### Claim 2 (depends on 1) The mobile device of claim 1 wherein the multi-level supply envelope tracker has a modulation bandwidth less than a full bandwidth of the radio frequency signal. ### Claim 3 (depends on 1) The mobile device of claim 1 wherein the multi-level supply envelope tracker includes a multi-level supply DC-to-DC converter configured to generate a plurality of regulated voltages of different voltage levels, a modulator configured to receive the plurality of regulated voltages and having an output configured to control the power amplifier supply voltage, and a control circuit configured to control the modulator based on the envelope signal. ### Claim 4 (depends on 3) The mobile device of claim 3 wherein the multi-level supply envelope tracker further includes a passive filter interposed between the output of the modulator and a supply input to the power amplifier. ### Claim 5 (depends on 4) The mobile device of claim 4 wherein the bias modulation circuit receives the power amplifier supply voltage from the output of the modulator prior to filtering by the passive filter, and the power amplifier receives the power amplifier supply voltage after filtering by the passive filter. ### Claim 6 (depends on 5) The mobile device of claim 5 wherein the power management circuit further includes a separate supply voltage filter operable to filter the power amplifier supply voltage to generate a filtered power amplifier supply voltage that serves as an input to the bias modulation circuit. ### Claim 7 (depends on 6) The mobile device of claim 6 wherein the separate supply voltage filter is programmable. ### Claim 8 (depends on 3) The mobile device of claim 3 wherein the modulator further includes a plurality of switches each electrically connected between a corresponding one of the plurality of regulated voltages and the output. ### Claim 9 (depends on 1) The mobile device of claim 1 wherein the programmable supply voltage filter is implemented as a low pass filter having a controllable corner frequency. ### Claim 10 An envelope tracking system comprising: a power amplifier configured to receive a radio frequency signal at a signal input and to provide an amplified radio frequency signal at a signal output, the power amplifier including an amplifier transistor configured to receive the radio frequency signal at a base, and a cascode transistor having an emitter connected to a collector of the amplifier transistor and a collector connected to the signal output; a multi-level supply envelope tracker configured to generate a power amplifier supply voltage of the power amplifier based on an envelope signal indicating an envelope of the radio frequency signal; a programmable supply voltage filter operable to filter the power amplifier supply voltage to generate a filtered power amplifier supply voltage; and a bias modulation circuit configured to modulate a bias of a base of the cascode transistor of the power amplifier based on a voltage level of the filtered power amplifier supply voltage. ### Claim 11 (depends on 10) The envelope tracking system of claim 10 wherein the multi-level supply envelope tracker has a modulation bandwidth less than a full bandwidth of the radio frequency signal. ### Claim 12 (depends on 10) The envelope tracking system of claim 10 wherein the multi-level supply envelope tracker includes a multi-level supply DC-to-DC converter configured to generate a plurality of regulated voltages of different voltage levels, a modulator configured to receive the plurality of regulated voltages and having an output configured to control the power amplifier supply voltage, and a control circuit configured to control the modulator based on the envelope signal. ### Claim 13 (depends on 12) The envelope tracking system of claim 12 wherein the multi-level supply envelope tracker further includes a passive filter interposed between the output of the modulator and a supply input to the power amplifier. ### Claim 14 (depends on 13) The envelope tracking system of claim 13 wherein the bias modulation circuit receives the power amplifier supply voltage from the output of the modulator prior to filtering by the passive filter, and the power amplifier receives the power amplifier supply voltage after filtering by the passive filter. ### Claim 15 (depends on 14) The envelope tracking system of claim 14 further comprising a separate supply voltage filter operable to filter the power amplifier supply voltage to generate a filtered power amplifier supply voltage that serves as an input to the bias modulation circuit. ### Claim 16 (depends on 15) The envelope tracking system of claim 15 wherein the separate supply voltage filter is programmable. ### Claim 17 A method of envelope tracking, the method comprising: receiving a radio frequency signal at a signal input of a power amplifier and providing an amplified radio frequency signal at a signal output of the power amplifier, the power amplifier including an amplifier transistor having a base receiving the radio frequency signal and a cascode transistor having an emitter connected to a collector of the amplifier transistor and a collector connected to the signal output; generating a power amplifier supply voltage of the power amplifier based on an envelope signal using a multi-level supply envelope tracker, the envelope signal indicating an envelope of the radio frequency signal; filtering the power amplifier supply voltage to generate a filtered power amplifier supply voltage using a programmable supply voltage filter; and modulating a bias of a base of the cascode transistor of the power amplifier based on a voltage level of the filtered power amplifier supply voltage using a bias modulation circuit. ### Claim 18 (depends on 17) The method of claim 17 wherein generating the power amplifier supply voltage includes generating a plurality of regulated voltages of different voltage levels using a multi-level supply DC-to-DC converter, and modulating the plurality of regulated voltages based on the envelope signal to generate the power amplifier supply voltage using a modulator. ### Claim 19 (depends on 18) The method of claim 18 further comprising filtering the power amplifier supply voltage using a passive filter interposed between an output of the modulator and a supply input to the power amplifier. ### Claim 20 (depends on 18) The method of claim 18 further comprising setting a corner frequency of the programmable supply voltage filter.