# US 6,400,233 B1 · Method and apparatus for compensating for distortion in IQ modulators > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,400,233 B1 - Document ID: US6400233B1 - Status: Granted - Kind: B1 - Application number: 09/743,454 - Filed: 2001-01-10 - Granted: 2002-06-04 - Earliest claimed: 1998-07-16 - Assignees: IFR, Inc. - Inventors: Neil E. Thomas - Web page: https://patentgrep.com/patent/US6400233B1 ## CPC - H03F 1/3241: {using predistortion circuits (H03F1/3211, H03F1/3217 take precedence)} - H03C 3/40: using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated - H03D 3/009: {Compensating quadrature phase or amplitude imbalances} - H04L 27/368: {adaptive predistortion} - H03F: AMPLIFIERS - H03C: MODULATION (masers or lasers H01S; coding, decoding or code conversion H03M) - H03D: DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER (masers, lasers H01S; circuits capable of acting both as modulator and demodulator H03C; details applicable to both modulators and frequency-changers H03C; demodulating pulses H03K9/00; transforming types of pulse modulation H03K11/00; coding, decoding or code conversion, in general H03M; repeater stations H04B7/14; demodulators adapted for AC systems of digital information transmission H04L27/00; synchronous demodulators adapted for colour television H04N9/66) - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A distortion compensating apparatus for use in IQ modulation and demodulation techniques wherein a first distortion arrangement distorts the I-signal by adding to the I-signal a first weighted function of the I-signal and a first weighted function of the Q-signal and a second distortion arrangement distorts for Q-signal by adding to the Q-signal a second weighted function of the I-signal and a second weighted function of the Q-signal, such that the weighted functions of the I-signal are independent of the Q-signal and the weighted functions of the Q-signal are independent of the I-signal. This enable distortions to be compensated in both sidebands of the IQ modulated signal. ## Claims ### Claim 1 A distortion compensating apparatus for use in IQ modulation and demodulation techniques wherein a first distortion arrangement distorts an I-signal by adding to the I-signal a first weighted non-linear function of the I-signal and a first weighted non-linear function of a Q-signal and a second distortion arrangement distorts the Q-signal by adding to the Q-signal a second weighted non-linear function of the I-signal and a second weighted non-linear function of the Q-signal, such that the weighted non-linear functions of the I-signal are independent of the Q-signal and the weighted non-linear functions of the Q-signal are independent of the I-signal. ### Claim 2 (depends on 1) An apparatus according to claim 1, comprising; a first operator arrangement for creating a function of the I-signal, a second operator arrangement for creating a function of the Q-signal, and, signal processing means for performing a weighted summation of the I-signal, the function of the I-signal and the function of the Q-signal to generate a distortion compensated I-signal output, and for performing a weighted summation of the Q-signal, the function of the Q-signal and the function of the I-signal to generate a distortion compensated Q-signal output. ### Claim 3 (depends on 1) An apparatus according to claim 1 wherein the function is a polynomial. ### Claim 4 (depends on 3) An apparatus according to claim 3 wherein the polynomial is cubic. ### Claim 5 (depends on 1) An apparatus according to claim 1 wherein the distorted I and Q-signals are amplitude modulated onto a single carrier signal by an IQ modulator. ### Claim 6 (depends on 1) An apparatus according to claim 1 wherein the I and Q-signals are demodulated from a single carrier signal by an IQ demodulation arrangement. ### Claim 7 (depends on 1) An apparatus according to claim 1 wherein at least one multiplier is used to multiply the function of the I and Q-signals by a weighting factor. ### Claim 8 (depends on 7) An apparatus according to claim 7 wherein at least one adder adds selected outputs of the one or more multipliers in order to perform weighted summations. ### Claim 9 (depends on 1) An apparatus according to claim 1 wherein a first multiplier multiplies the function of the I-signal with a first constant weighting factor and a second multiplier multiplies the function of the Q-signal with a second constant weighting factor. ### Claim 10 (depends on 9) An apparatus according to claim 9 wherein a third multiplier multiplies the function of the Q-signal with a third constant weighting factor and a fourth multiplier multiplies the function of the I-signal with a fourth constant weighting factor. ### Claim 11 (depends on 9) An apparatus according to claim 9 wherein, an adder adds the output from the first multiplier and the second multiplier to the I-signal. ### Claim 12 (depends on 10) An apparatus according to claim 10 wherein an adder adds the output from the multiplier and the fourth multiplier to the Q-signal. ### Claim 13 (depends on 7) An apparatus according to claim 7 wherein said at least one of the multipliers is implemented as a look up table. ### Claim 14 (depends on 2) An apparatus according to claim 2 wherein at least one of the operator arrangements is implemented as a look up table. ### Claim 15 A method for improving linearity in IQ modulation and demodulation techniques comprising steps wherein an I-signal is distorted by adding to the I-signal a first weighted non-linear function of the I-signal and a first weighted non-linear function of a Q-signal and the Q-signal is distorted by adding to the Q-signal a second weighted non-linear function of the I-signal and a second weighted non-linear function of the Q-signal, such that the weighted functions of the I-signal are independent of the Q-signal and the weighted functions of the Q-signal are independent of the I-signal. ### Claim 16 (depends on 15) A method according claim 15, further comprising steps of; generating a function of the I-signal, generating a function of the Q-signal, performing a weighted summation of the I-signal, the function of the I-signal and the function of the Q-signal to generate a distortion compensated I-signal output, and performing a weighted summation of the Q-signal, the function of the Q-signal and the function of the I-signal to generate a distortion compensated Q-signal output. ### Claim 17 (depends on 15) A method according to claim 15 wherein the function is a polynomial. ### Claim 18 (depends on 17) A method according to claim 17 wherein the polynomial is cubic. ### Claim 19 (depends on 15) A method according to claim 15 wherein at least one of the function of the I,Q signals is multiplied by one or more weighting factors. ### Claim 20 (depends on 19) A method according to claim 19 wherein selected multiplied functions of the I,Q signals are added to perform the weighted summation. ### Claim 21 (depends on 1) A device for adjusting a composite IQ modulator or demodulator which composite IQ modulator or demodulator comprises a distortion compensating apparatus according to claim 1 and an IQ modulator or demodulator, which device comprises; a spectrum analyser for measuring the level of distortion in the output of a composite IQ modulator or demodulator; and a control processor for controlling the weighting of the functions of the I and Q-signals in a composite IQ modulator or demodulator. ### Claim 22 (depends on 21) A device according to claim 21 which includes a signal source for generating test signals.