# US 10,873,299 B2 · Trans-impedance amplifier transfer function compensation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,873,299 B2 - Document ID: US10873299B2 - Status: Granted - Kind: B2 - Application number: 16/366,108 - Filed: 2019-03-27 - Published: 2020-10-01 - Granted: 2020-12-22 - Earliest claimed: 2019-03-27 - Assignees: Intel Corporation - Applicants: Intel Corporation - Inventors: Daniel Wimmer - Web page: https://patentgrep.com/patent/US10873299B2 ## CPC - H03F 1/083: {in transistor amplifiers (H03F1/10 - H03F1/22 take precedence)} - H03F 1/26: Modifications of amplifiers to reduce influence of noise generated by amplifying elements - H03F 1/56: Modifications of input or output impedances, not otherwise provided for - H03F 3/195: in integrated circuits - H03F 3/20: Power amplifiers, e.g. Class B amplifiers, Class C amplifiers (H03F3/26 - H03F3/30 take precedence) - H03F 3/245: {with semiconductor devices only} - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03F 2200/451: the amplifier being a radio frequency amplifier - H03F 2203/45512: the FBC comprising one or more capacitors, not being switched capacitors, and being coupled between the LC and the IC - H03F: AMPLIFIERS ## Abstract Techniques are disclosed to compensate for changes in the impedance of stage(s) preceding a trans-impedance amplifier (TIA) that is used within an RF chain. The techniques identify the changes in the source impedance value of the input stage (e.g., the mixers and LNAs) as a result of a gain state change, which alters the signal-to-transfer function (STF) of the TIA during operation and negatively impacts radio performance. The STF is maintained for changes in the source impedance value throughout different gain states without using switchable shunt components by using tunable elements to compensate for the source impedance changes, thus keeping the STF constant. ## Claims ### Claim 1 A filter circuit having a signal-transfer function (STF), the filter circuit comprising: an input stage coupled to a source impedance, the source impedance being associated with at least one preceding stage having an adjustable gain that, when changed, results in a change in the source impedance; an output stage; and at least one tunable component coupled between the input stage and the output stage, wherein a value of the at least one tunable component is adjustable to maintain the STF as the source impedance changes as a result of changes in the adjustable gain of the at least one preceding stage, wherein the source impedance is determined based upon values that correlate changes of the source impedance to changes in the adjustable gain of the at least one preceding stage, and wherein the value of the at least one tunable component is adjusted based upon the determined source impedance. ### Claim 2 (depends on 1) The filter circuit of claim 1, wherein the filter circuit includes an operational amplifier coupled to the input stage and the output stage such that the filter circuit functions as a 2nd-order low-pass trans-impedance amplifier (TIA). ### Claim 3 (depends on 1) The filter circuit of claim 1, wherein the filter circuit is included within a receive chain, the filter circuit being coupled between a mixer and an analog-to-digital converter (ADC). ### Claim 4 (depends on 1) The filter circuit of claim 1, wherein the at least one tunable component is at least one tunable capacitor, and wherein a capacitance of the at least one tunable capacitor is adjusted to maintain the STF as the source impedance changes. ### Claim 5 (depends on 1) The filter circuit of claim 1, wherein: the filter circuit includes an operational amplifier coupled to the input stage to provide a differential voltage signal Vout at the output stage, the filter circuit is symmetric with respect to the operational amplifier, the filter circuit having (i) each input of the operational amplifier coupled to a resistor R1, (ii) outer feedback paths including a resistor R2, (iii) inner feedback paths including a tunable capacitor C2, and (iv) a tunable capacitor C1 coupled across two terminals that form the input stage. ### Claim 6 (depends on 5) The filter circuit of claim 5, wherein: the input stage receives a current Iin, the source impedance is represented by a parallel combination of a resistance RS and a capacitance CS, and the STF of the filter circuit is defined by the following equation in the s-domain: V o ⁢ u ⁢ t I in = H S ⁢ T ⁢ F ⁡ ( s ) = - 2 ⁢ R 2 2 ⁢ s 2 ⁡ ( C 1 + C S ) ⁢ C 2 ⁢ R 1 ⁢ R 2 ⁢ R S + sC 2 ⁡ ( R 2 ⁡ ( 1 + 2 ⁢ R 1 R S ) + R 1 ) + 1 . ### Claim 7 (depends on 6) The filter circuit of claim 6, wherein capacitance values of the capacitors C1 and C2 are adjusted to compensate for changes in the source impedance based upon an evaluation of (i) 2s2 (C1+CS)C2R1R2RS, and (ii) s ⁢ C 2 ⁡ ( R 2 ⁡ ( 1 + 2 ⁢ R 1 R S ) + R 1 ) , to maintain the STF substantially constant as the gain of the at least one preceding stage is adjusted. ### Claim 8 A device, comprising: a transceiver chain including: a filter circuit having a signal-transfer function (STF), the filter circuit having (i) an input stage coupled to a source impedance, the source impedance being associated with at least one preceding stage having an adjustable gain that, when changed, results in a change in the source impedance, (ii) an output stage, and (iii) at least one tunable component coupled between the input stage and the output stage; and processing circuitry configured to: adjust a value of the at least one tunable component to maintain the STF as the source impedance changes as a result of changes in the adjustable gain of the at least one preceding stage, calculate the source impedance based upon values that correlate changes of source impedance to changes in adjustable gain of the at least one preceding stage, and adjust the value of the at least one tunable component based upon the calculated source impedance. ### Claim 9 (depends on 8) The device of claim 8, wherein the filter circuit includes an operational amplifier coupled to the input stage and the output stage such that the filter circuit functions as a 2nd-order low-pass trans-impedance amplifier (TIA). ### Claim 10 (depends on 8) The device of claim 8, wherein the filter circuit is coupled between a mixer and an analog-to-digital converter (ADC). ### Claim 11 (depends on 8) The device of claim 8, wherein the at least one tunable component is a tunable capacitor, and wherein the processing circuitry is configured to adjust a capacitance of the at least one tunable capacitor to maintain the STF as the source impedance changes. ### Claim 12 (depends on 8) The device of claim 8, wherein: the filter circuit includes an operational amplifier coupled to the input stage to provide a differential voltage signal Vout at the output stage, and the filter circuit is symmetric with respect to the operational amplifier, the filter circuit having (i) each input of the operational amplifier being coupled to a resistor R1, (ii) outer feedback paths including a resistor R2, (iii) inner feedback paths including a tunable capacitor C2, and (iv) a tunable capacitor C1 coupled across two terminals that form the input stage. ### Claim 13 (depends on 12) The filter circuit of claim 12, wherein: the input stage receives a current Iin, the source impedance is represented by a parallel combination of a resistance RS and a capacitance CS, and the STF of the filter circuit is defined by the following equation in the s-domain: V o ⁢ u ⁢ t I in = H S ⁢ T ⁢ F ⁡ ( s ) = - 2 ⁢ R 2 2 ⁢ s 2 ⁡ ( C 1 + C S ) ⁢ C 2 ⁢ R 1 ⁢ R 2 ⁢ R S + sC 2 ⁡ ( R 2 ⁡ ( 1 + 2 ⁢ R 1 R S ) + R 1 ) + 1 . ### Claim 14 (depends on 13) The device of claim 13, wherein the processing circuitry is configured to adjust capacitance values of the capacitors C1 and C2 to compensate for changes in the source impedance based upon an evaluation of (i) 2s2(C1+Cs)C2R1R2RS, and (ii) s ⁢ C 2 ⁡ ( R 2 ⁡ ( 1 + 2 ⁢ R 1 R S ) + R 1 ) , to maintain the STF substantially constant as the gain of the at least one preceding stage is adjusted. ### Claim 15 A computer-implemented method for tuning a filter circuit having a signal-transfer function (STF), the method comprising: determining, by one or more processors, a gain state of at least one preceding stage associated with a source impedance with respect to the filter circuit, the at least one preceding stage having an adjustable gain that, when changed, results in a change in the source impedance; determining, by the one or more processors, a source impedance value associated with a current gain state of the at least one preceding stage; evaluating, by the one or more processors, tuning values for the filter circuit for the determined source impedance value; and transmitting, by the one or more processors, tuning control signals to the filter circuit to cause the filter circuit to adjust a value of at least one tunable component within the filter circuit in accordance with the tuning values to maintain the STF as the source impedance changes as a result of changes in the adjustable gain of the at least one preceding stage. ### Claim 16 (depends on 15) The computer-implemented method of claim 15, wherein the at least one tunable component is a tunable capacitor, and wherein the tuning control signals adjust a capacitance of the at least one tunable component to maintain the STF as the source impedance changes. ### Claim 17 (depends on 15) The computer-implemented method of claim 15, wherein determining the source impedance includes comparing a current gain of the at least one preceding stage to a lookup table (LUT) of values that correlate changes of source impedance to changes in adjustable gain of the at least one preceding stage. ### Claim 18 (depends on 15) The computer-implemented method of claim 15, wherein determining the source impedance includes evaluating an equation that identifies changes of the source impedance as a function of changes in the adjustable gain of the at least one preceding stage.