# US 10,374,581 B2 · Digital filter circuit, signal processing device, and digital filter processing method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,374,581 B2 - Document ID: US10374581B2 - Status: Granted - Kind: B2 - Application number: 15/544,042 - Filed: 2016-01-14 - Published: 2018-01-11 - Granted: 2019-08-06 - Earliest claimed: 2015-01-21 - Assignees: NEC Corporation - Applicants: NEC Corporation - Inventors: Atsufumi Shibayama; Junichi Abe; Kohei Hosokawa - Web page: https://patentgrep.com/patent/US10374581B2 ## CPC - H03H 17/0248: {Filters characterised by a particular frequency response or filtering method} - G06F 17/14: Fourier, Walsh or analogous domain transformations {, e.g. Laplace, Hilbert, Karhunen-Loeve, transforms (for correlation function computation G06F17/156; spectrum analysers G01R23/16)} - H03H 17/0202: {Two or more dimensional filters; Filters for complex signals (multidimensional convolutions G06F17/153)} - H03H 17/0213: {Frequency domain filters using Fourier transforms} - H03H 2017/0245: {Measures to reduce power consumption} - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract Provided is a digital filter circuit in which a filter coefficient can be easily changed, for which circuit scale and power consumption can be reduced, and which carries out digital filter processing in a frequency domain. This digital filter circuit includes: a separating circuit for separating a first complex number signal, of a frequency domain that was subjected to Fourier transform, into a real number portion and an imaginary number portion; a filter coefficient generating circuit for generating a first frequency domain filter coefficient from a first input filter coefficient and a third input filter coefficient, and for generating a second frequency domain filter coefficient from a second input filter coefficient and the third input filter coefficient; a first filter that filters the separated real number portion using the first frequency domain filter coefficient; a second filter that filters the separated imaginary number portion using the second frequency domain filter coefficient; and a combining circuit for combining the output from the two filters. ## Claims ### Claim 1 A digital filter circuit comprising: a separating circuit implemented in hardware and configured to separate a first complex-number signal in a frequency domain, into which a complex-number signal in a time domain has been transformed through a Fourier transform, into a second complex-number signal in the frequency domain and a third complex-number signal in the frequency domain, the second complex-number signal corresponding to a real part of the complex-number signal in the time domain, and the third complex-number signal corresponding to an imaginary part of the complex-number signal in the time domain; a filter coefficient generating circuit implemented in the hardware and configured to accept inputted first, second, and third input filter coefficients that are complex-numbers, and generating a first frequency-domain filter coefficient that is a complex number from the first input filter coefficient and third input filter coefficients, and generating a second frequency-domain filter coefficient that is a complex number from the second input filter coefficient and the third input filter coefficient; a first filter implemented in the hardware and for performing a filtering process on the second complex-number signal with the first frequency-domain filter coefficient and outputting a fourth complex-number signal; a second filter implemented in the hardware and for performing a filtering process on the third complex-number signal with the second frequency-domain filter coefficient and outputting a fifth complex-number signal; and a combining circuit implemented in the hardware and configured to combine the fourth complex-number signal with the fifth complex-number signal and generating a sixth complex-number signal, wherein performing filtering by the digital filter circuit in a frequency domain instead of in the time domain reduces circuit size and power consumption. ### Claim 2 (depends on 1) The digital filter circuit according to claim 1, wherein the first, second, and third input filter coefficients are complex-number filter coefficients for a filtering process in a frequency domain, wherein the first input filter coefficient corresponds to a filter coefficient for real-number calculation on a real part of the complex-number signal in the time domain in a time-domain filtering process, that is a filtering process in the time domain on the complex-number signal in the time domain, wherein the second input filter coefficient corresponds to a filter coefficient for real-number calculation on an imaginary part of the complex-number signal in the time domain in the time-domain filtering process, and wherein the third input filter coefficient corresponds to a filter coefficient for complex-number calculation on the complex-number signal in the time domain in the time-domain filtering process. ### Claim 3 (depends on 2) The digital filter circuit according to claim 2, further comprising: a Fourier transform circuit configured to transform the inputted complex-number input signal in the time domain into the first complex-number signal through the Fourier transform; and an inverse Fourier transform circuit configured to transform the sixth complex-number signal into a complex-number signal in a time domain through an inverse Fourier transform. ### Claim 4 (depends on 3) The digital filter circuit according to claim 3, wherein the filter coefficient generating circuit generates the first frequency-domain filter coefficient by performing a complex multiplication of the first input filter coefficient by the third input filter coefficient, and generates the second frequency-domain filter coefficient by performing a complex multiplication of the second input filter coefficient by the third input filter coefficient. ### Claim 5 (depends on 2) The digital filter circuit according to claim 2, wherein the filter coefficient generating circuit generates the first frequency-domain filter coefficient by performing a complex multiplication of the first input filter coefficient by the third input filter coefficient, and generates the second frequency-domain filter coefficient by performing a complex multiplication of the second input filter coefficient by the third input filter coefficient. ### Claim 6 (depends on 1) The digital filter circuit according to claim 1, further comprising: a Fourier transform circuit implemented in the hardware and configured to transform the inputted complex-number input signal in the time domain into the first complex-number signal through the Fourier transform; and an inverse Fourier transform circuit implemented in the hardware and configured to transform the sixth complex-number signal into a complex-number signal in a time domain through an inverse Fourier transform. ### Claim 7 (depends on 6) The digital filter circuit according to claim 6, wherein when N is a number of samples transformed through the Fourier transform and is an integer satisfying N>0, the Fourier transform circuit outputs, as the first complex-number signal, a complex-number signal X(k) and a complex-number signal X(N−k), where k is a frequency number satisfying 0≤k≤N−1, wherein the separating circuit comprises: a generating circuit configured to generate a complex conjugate X*(N−k) of the outputted complex-number signal X(N−k); a first adding circuit configured to add a real part of the outputted complex-number signal X(k) to a real part of the generated complex conjugate X*(N−k); a second adding circuit configured to add an imaginary part of the outputted complex-number signal X(k) to an imaginary part of the generated complex conjugate X*(N−k); a first subtracting circuit configured to subtract a real part of the generated complex conjugate X*(N−k) from a real part of the outputted complex-number signal X(k); a second subtracting circuit configured to subtract an imaginary part of the generated complex conjugate X*(N−k) from an imaginary part of the outputted complex-number signal X(k); a first multiplying circuit configured to multiply an output from the first adding circuit by ½; a second multiplying circuit configured to multiply an output from the second adding circuit by ½; a third multiplying circuit configured to multiply an output from the first subtracting circuit by ½; and a fourth multiplying circuit configured to multiply an output from the second subtracting circuit by ½, and wherein the second complex-number signal is generated from outputs from the first multiplying circuit and second multiplying circuit, and the third complex-number signal is generated from outputs from the third and fourth multiplying circuits. ### Claim 8 (depends on 7) The digital filter circuit according to claim 7, wherein the first filter outputs a fourth complex-number signal XI′(k), where k is a frequency number satisfying 0≤k≤N−1, wherein the second filter outputs a fifth complex-number signal XQ′(k), where k is a frequency number satisfying 0≤k≤N−1, wherein the combining circuit comprises: a third adding circuit configured to add a real part of the fourth complex-number signal XI′(k) to a real part of the fifth complex-number signal XQ′(k); and a fourth adding circuit configured to add an imaginary part of the fourth complex-number signal XI′(k) to an imaginary part of the fifth complex-number signal XQ′(k), and wherein the sixth complex-number signal is generated from outputs from the third and fourth adding circuits. ### Claim 9 (depends on 6) The digital filter circuit according to claim 6, wherein the filter coefficient generating circuit generates the first frequency-domain filter coefficient by performing a complex multiplication of the first input filter coefficient by the third input filter coefficient, and generates the second frequency-domain filter coefficient by performing a complex multiplication of the second input filter coefficient by the third input filter coefficient. ### Claim 10 (depends on 1) The digital filter circuit according to claim 1, wherein the filter coefficient generating circuit generates the first frequency-domain filter coefficient by performing a complex multiplication of the first input filter coefficient by the third input filter coefficient, and generates the second frequency-domain filter coefficient by performing a complex multiplication of the second input filter coefficient by the third input filter coefficient. ### Claim 11 (depends on 1) A signal processing device comprising: the digital filter circuit according to claim 1. ### Claim 12 A digital filter processing method, performing by a digital filter circuit, the method comprising: separating a first complex-number signal in a frequency domain, into which a complex-number signal in a time domain has been transformed through a Fourier transform, into a second complex-number signal in the frequency domain and a third complex-number signal in the frequency domain, the second complex-number signal corresponding to a real part of the complex-number signal in the time domain, and the third complex-number signal corresponding to an imaginary part of the complex-number signal in the time domain; generating a first frequency-domain filter coefficient that is a complex-number from a first input filter coefficient and a third input filter coefficient that are complex-numbers and have been inputted; generating a second frequency-domain filter coefficient that is a complex-number from a second input filter coefficient that is a complex-number and the third input filter coefficients that have been inputted; performing a filtering process on the second complex-number signal with the first frequency-domain filter coefficient and outputting a fourth complex-number signal; performing a filtering process on the third complex-number signal with the second frequency-domain filter coefficient and outputting a fifth complex-number signal; and combining the fourth complex-number signal with the fifth complex-number signal and generating a sixth complex-number signal, wherein performing filtering by the digital filter circuit in the frequency domain instead of in the time domain reduces circuit size and power consumption. ### Claim 13 (depends on 12) The digital filter processing method according to claim 12, wherein the first input filter coefficient is a complex-number filter coefficient in a frequency domain, the complex-number filter coefficient corresponding to a filter coefficient for real-number calculation on a real part of the complex-number signal in the time domain in a time-domain filtering process that is a filtering process in the time domain on the complex-number signal in the time domain, wherein the second input filter coefficient is a complex-number filter coefficient in a frequency domain, the complex-number filter coefficient corresponding to a filter coefficient for real-number calculation on an imaginary part of the complex-number signal in the time domain in the time-domain filtering process, and wherein the third input filter coefficient is a complex-number filter coefficient in a frequency domain, the complex-number filter coefficient corresponding to a filter coefficient for complex-number calculation on the complex-number signal in the time domain in the time-domain filtering process. ### Claim 14 (depends on 13) The digital filter processing method according to claim 13, the method comprising: transforming an inputted complex-number input signal in a time domain into the first complex-number signal through a Fourier transform; and transforming the sixth complex-number signal generated into a complex-number signal in a time domain through an inverse Fourier transform. ### Claim 15 (depends on 12) The digital filter processing method according to claim 12, the method comprising: transforming an inputted complex-number input signal in a time domain into the first complex-number signal through a Fourier transform; and transforming the sixth complex-number signal generated into a complex-number signal in a time domain through an inverse Fourier transform.