# US 2013/0154738 A1 · Amplifier and filter having variable gain and cutoff frequency controlled logarithmically according to digital code > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0154738 A1 - Document ID: US20130154738A1 - Status: Published application - Kind: A1 - Application number: 13/713,582 - Filed: 2012-12-13 - Published: 2013-06-20 - Earliest claimed: 2011-12-16 - Assignees: Samsung Electronics Co., Ltd. - Inventors: Jong-Woo LEE - Web page: https://patentgrep.com/patent/US20130154738A1 ## CPC - H03G 3/002: {Control of digital or coded signals (H03G3/3089 take precedence)} - H03F 3/45475: {using IC blocks as the active amplifying circuit} - H03G 1/0088: {using discontinuously variable devices, e.g. switch-operated} - H03G 3/001: {Digital control of analog signals} - H03G 9/20: in frequency-selective amplifiers - H03H 11/1291: {Current or voltage controlled filters} - H03F 2203/45512: the FBC comprising one or more capacitors, not being switched capacitors, and being coupled between the LC and the IC - H03F 2203/45522: the FBC comprising one or more potentiometers - H03G: CONTROL OF AMPLIFICATION - H03F: AMPLIFIERS - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) ## Abstract A variable gain amplifier circuit is provided. The circuit includes an operational amplifier for amplifying and outputting an input signal according to a cutoff frequency and a gain, a feedback resistor for changing a first resistance according to a first digital control code value which determines the cutoff frequency, and an input resistor for changing a second resistance according to a second digital control code value which is determined based on a difference of the first digital control code value and a gain code value. The gain is determined by a ratio of the first resistance and the second resistance and linearly changes on a decibel (dB) basis according to the first digital control code value, the cutoff frequency is inversely proportional to the first resistance and linearly changes on a log scale, and the variable gain can be easily set using the control code. ## Claims ### Claim 1 A variable gain amplifier circuit comprising: an operational amplifier for amplifying and outputting an input signal according to a cutoff frequency and a gain; a feedback resistor for changing a first resistance according to a first digital control code value which determines the cutoff frequency; and an input resistor for changing a second resistance according to a second digital control code value which is determined based on a difference of the first digital control code value and a gain code value, wherein the gain is determined by a ratio of the first resistance and the second resistance and linearly changes on a decibel (dB) basis according to the first digital control code value, and wherein the cutoff frequency is inversely proportional to the first resistance and linearly changes on a log scale. ### Claim 2 (depends on 1) The variable gain amplifier circuit of claim 1, wherein the gain is determined by and proportional to a difference of the first digital control code value and the second digital control code value on the dB basis. ### Claim 3 (depends on 1) The variable gain amplifier circuit of claim 1, further comprising: a feedback capacitor connected between an input stage and an output stage of the operational amplifier. ### Claim 4 (depends on 1) The variable gain amplifier circuit of claim 1, further comprising: a logic circuit for applying an AND operation and a NOT operation to bit values corresponding to the first digital control code or the second digital control code. ### Claim 5 (depends on 1) The variable gain amplifier circuit of claim 1, wherein a sum of the first digital control code for controlling the cutoff frequency, and a third digital control code for determining a quality factor which determines a performance of a filter function determines the quality factor. ### Claim 6 (depends on 1) The variable gain amplifier circuit of claim 1, wherein the second digital control code value is determined based on the following equation: Code2=K Code1=K−n*Gain_Code where Code2 denotes a digital control code for determining the feedback resistor, Code1 denotes a digital control code for the input resistor, K denotes an integer according to a digital control code size N, Gain_Code denotes an integer for determining the gain, and n denotes an integer determined by the digital control code size N. ### Claim 7 (depends on 1) The variable gain amplifier circuit of claim 1, wherein the feedback resistor comprises: a first resistor segment; a plurality of second resistor segments connected to the first resistor segment in series; a first switch connected to both ends of the second resistor segments and controlled by the first control code; and a second switch connected to the second resistor segments in series and controlled by an inverse signal of the first control code. ### Claim 8 (depends on 7) The variable gain amplifier circuit of claim 7, wherein the first resistance controlled by the first digital control code is determined based on a geometric progression of resistances corresponding to the first resistor segment and the second resistor segments. ### Claim 9 (depends on 7) The variable gain amplifier circuit of claim 7, further comprising: a logic circuit for correcting an error of differential resistances by adding an additional digital control code value to part of the segments of the feedback resistor. ### Claim 10 (depends on 1) The variable gain amplifier circuit of claim 1, wherein the input resistor comprises: a first resistor segment; a plurality of second resistor segments connected to the first resistor segment in series; a first switch connected to both ends of the second resistor segments and controlled by the second control code; and a second switch connected to the second resistor segments in series and controlled by an inverse signal of the second control code. ### Claim 11 (depends on 10) The variable gain amplifier circuit of claim 10, wherein the second resistance controlled by the second digital control code is determined based on a geometric progression of resistances corresponding to the first resistor segment and the second resistor segments. ### Claim 12 (depends on 10) The variable gain amplifier circuit of claim 10, further comprising: a logic circuit for correcting an error of differential resistances by adding an additional digital control code value to part of the segments of the input resistor. ### Claim 13 A variable gain amplifier circuit comprising: a logic circuit for applying an AND operation and a NOT operation to a first digital control code for determining a cutoff frequency and a second digital control code determined based on a difference of the first digital control code and a gain code value; a feedback resistor for changing a first resistance according to the first digital control code value; an input resistor for changing a second resistance according to the second digital control code value; and an operational amplifier for amplifying and outputting an input signal according to the cutoff frequency and a gain, wherein the gain is determined by a ratio of the first resistance and the second resistance and linearly changes on a decibel (dB) basis according to the first digital control code value, and wherein the cutoff frequency is inversely proportional to the first resistance and linearly changes on a log scale. ### Claim 14 (depends on 13) The variable gain amplifier circuit of claim 13, wherein the gain is proportional on the dB basis based on a difference of the first digital control code and the second digital control code. ### Claim 15 (depends on 13) The variable gain amplifier circuit of claim 13, further comprising: a feedback capacitor connected between an input stage and an output stage of the operational amplifier. ### Claim 16 (depends on 13) The variable gain amplifier circuit of claim 13, wherein the feedback resistor or the input resistor comprises: a first resistor segment; a plurality of second resistor segments connected to the first resistor segment in series; a first switch connected to both ends of the second resistor segments and controlled by the first control code; and a second switch connected to the second resistor segments in series and controlled by an inverse signal of the first control code. ### Claim 17 (depends on 16) The variable gain amplifier circuit of claim 16, wherein the first resistance controlled by the first digital control code is determined based on a geometric progression of resistances corresponding to the first resistor segment and the second resistor segments. ### Claim 18 (depends on 13) The variable gain amplifier circuit of claim 13, further comprising: a logic circuit for correcting an error of differential resistances by adding an additional digital control code value to part of the segments of the feedback resistor.