# US 2013/0154728 A1 · Adaptive Filtering of Blocker Signals in Demodulators > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0154728 A1 - Document ID: US20130154728A1 - Status: Published application - Kind: A1 - Application number: 13/328,388 - Filed: 2011-12-16 - Published: 2013-06-20 - Earliest claimed: 2011-12-16 - Assignees: Infineon Technologies AG - Inventors: Umut Basaran; Ashkan Naeini - Web page: https://patentgrep.com/patent/US20130154728A1 ## CPC - H03F 1/086: {with FET's} - 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 3/45183: {Long tailed pairs (H03F3/4521, H03F3/45237 take precedence)} - H03F 3/45188: {Non-folded cascode stages} - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03H 11/0422: {using transconductance amplifiers, e.g. gmC filters} - H03F 2203/45138: Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers - H03F 2203/45521: the FBC comprising op amp stages, e.g. cascaded stages of the dif amp and being coupled between the LC and the IC - H03F 2203/45526: the FBC comprising a resistor-capacitor combination and being coupled between the LC and the IC - H03F 2203/45534: the FBC comprising multiple switches and being coupled between the LC and the IC - H03F: AMPLIFIERS - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) ## Abstract Some embodiments of the invention relate a transimpedance amplifier circuit having a negative feedback network that provides additional filtering of an out-of-band transmitted signal is provided herein. In one embodiment, the transimpedance amplifier circuit has a first pole, transimpedance amplifier having a multi-stage operational amplifier with an input terminal and an output terminal. An RC feedback network extends from the output terminal to the input terminal. A negative feedback network, extending from an internal node of the multi-stage operational amplifier to an input terminal of the single pole, transimpedance amplifier provides a negative feedback signal with an amplitude having an opposite polarity as the out-of-band transmitted signal. The negative feedback signal suppresses the out-of-band-transmitted signals within the demodulator circuit, thereby improving linearity of the transimpedance amplifier circuit. ## Claims ### Claim 1 A demodulator circuit, comprising: a transimpedance amplifier configured to receive an input signal having out-of-band transmitted signals, comprising: a first operational amplifier having an input terminal and an output terminal; a first RC feedback network extending from the output terminal to the input terminal; and a negative feedback network extending from the transimpedance amplifier to an input terminal of the transimpedance amplifier, wherein the negative feedback network is configured to provide a negative feedback signal for common mode and differential input signals that suppresses out-of-band-transmitted signals within the input signal. ### Claim 2 (depends on 1) The demodulator circuit of claim 1, wherein the first operational amplifier comprises a first operational amplifier stage and a second operational amplifier stage, located downstream of the first operational amplifier stage. ### Claim 3 (depends on 2) The demodulator circuit of claim 2, wherein the negative feedback network extends from an internal node of the first operational amplifier to the input terminal of the transimpedance amplifier. ### Claim 4 (depends on 1) The demodulator circuit of claim 1, wherein the negative feedback network comprises a negative feedback filtering element configured to provide the negative feedback signal having a frequency corresponding to a frequency of the out-of-band transmitted signals. ### Claim 5 (depends on 4) The demodulator circuit of claim 4, wherein the negative feedback filtering element comprises a second operational amplifier connected in parallel to a second RC feedback network. ### Claim 6 (depends on 4) The demodulator circuit of claim 4, wherein a number of operational amplifier stages between the input terminal of the first operational amplifier and the input terminal of the transimpedance amplifier, along the negative feedback network, is an odd number. ### Claim 7 (depends on 4) The demodulator circuit of claim 4, further comprising: one or more switches connected between the internal node of the first operational amplifier and the negative feedback filtering element; and a control unit configured to generate a control signal that selectively opens and closes the one or more switches to connect or disconnect the negative feedback network from the transimpedance amplifier. ### Claim 8 (depends on 7) The demodulator circuit of claim 7, wherein the control unit is configured to selective open the one or more switches when a transmitted signal, which is the source of the out-of-band transmitted signals, has a power that is below a predetermined power threshold; and wherein the control unit is configured to selective close the one or more switches when the transmitted signal, which is the source of the out-of-band transmitted signals, has a power that exceeds the predetermined power threshold. ### Claim 9 A transimpedance amplifier (TIA) circuit, comprising, a transimpedance amplifier configured to filter a differential input signal having out-of-band transmitted signals; and a negative feedback network, extending from an internal node within the transimpedance amplifier to an input terminal of the transimpedance amplifier, and configured to provide a negative feedback signal having a frequency that corresponds to the frequency of the out-of-band transmitted signals and an amplitude having an opposite polarity as the out-of-band transmitted signals. ### Claim 10 (depends on 9) The TIA circuit of claim 9, wherein the transimpedance amplifier comprises: a first multi-stage operational amplifier having a first operational amplifier stage and a second operational amplifier stage located downstream of the first operational amplifier stage; and a first RC feedback network extending from an output terminal of the second operational amplifier stage to an input terminal of the first operational amplifier stage. ### Claim 11 (depends on 10) The TIA circuit of claim 10, wherein an odd number of operational amplifier stages are configured between the input of the first multi-stage operational amplifier and the input of the transimpedance amplifier, along the negative feedback network. ### Claim 12 (depends on 10) The TIA circuit of claim 10, wherein the negative feedback network comprises a negative feedback filtering element comprising an active band pass or high pass filter. ### Claim 13 (depends on 12) The TIA circuit of claim 12, wherein the negative feedback filtering element comprises a second multi-stage operational amplifier connected in parallel to a second RC feedback network. ### Claim 14 (depends on 12) The TIA circuit of claim 12, further comprising: one or more switches connected between the internal node of the first multi-stage operational amplifier and the negative feedback filtering element; and a control unit configured to generate a control signal that selectively opens and closes the one or more switches to connect or disconnect the negative feedback network and the transimpedance amplifier. ### Claim 15 (depends on 14) The TIA circuit of claim 14, wherein the control unit is configured to selective open the one or more switches when a transmitted signal, which is the source of the out-of-band transmitted signals, has a power that is below a predetermined power threshold; and wherein the control unit is configured to selective close the one or more switches when the transmitted signal, which is the source of the out-of-band transmitted signals, has a power that exceeds the predetermined power threshold. ### Claim 16 (depends on 9) The TIA circuit of claim 9, wherein the negative feedback network is configured to generate negative feedback signals for the differential and common-mode input signals. ### Claim 17 A method for improving linearity of a transimpedance amplifier circuit, comprising: providing a current signal to a first pole transimpedance amplifier comprising a multi-stage operational amplifier having a first operational amplifier stage and a last operational amplifier stage; providing a first amplified signal to a filter within a feedback loop extending from an output terminal of the last operational amplifier stage to an input terminal of the first operational amplifier stage; providing a second amplified signal from an internal node of the multi-stage operational amplifier to a negative feedback network configured to provide a negative feedback signal; and providing the negative feedback signal to an input terminal of the first pole transimpedance amplifier to suppress out-of-band-transmitted signals within the transimpedance amplifier circuit. ### Claim 18 (depends on 17) The method of claim 17, wherein the second amplified signal is provided from an internal node comprising an output of the first operational amplifier stage. ### Claim 19 (depends on 17) The method of claim 17, further comprising: selectively connecting or disconnecting the negative feedback network to the internal node of the multi-stage operational amplifier. ### Claim 20 (depends on 19) The method of claim 19, wherein the negative feedback network is selectively disconnected from the internal node of the multi-stage operational amplifier when a transmitted signal, which is the source of the out-of-band transmitted signals, has a power that is below a predetermined power threshold; and wherein the negative feedback network is selectively connected to the internal node of the multi-stage operational amplifier when a transmitted signal, which is the source of the out-of-band transmitted signals, has a power that exceeds a predetermined power threshold.