# US 11,909,400 B2 · Use of stable tunable active feedback analog filters in frequency synthesis > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,909,400 B2 - Document ID: US11909400B2 - Status: Granted - Kind: B2 - Application number: 17/782,103 - Filed: 2020-12-04 - Published: 2023-01-05 - Granted: 2024-02-20 - Earliest claimed: 2019-12-05 - Assignees: Anlotek Limited - Applicants: Anlotek Limited - Inventors: Jorgen Staal Nielsen - Web page: https://patentgrep.com/patent/US11909400B2 ## CPC - G06F 1/0321: {Waveform generators, i.e. devices for generating periodical functions of time, e.g. direct digital synthesizers (G06F1/0314, G06F1/035 take precedence)} - H03K 5/1252: Suppression or limitation of noise or interference (specially adapted for transmission systems H04B15/00, H04L25/08) - H03H 7/0161: {Bandpass filters (H03H7/12 takes precedence)} - H03H 7/12: Bandpass or bandstop filters with adjustable bandwidth and fixed centre frequency (H03H7/09 takes precedence) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) ## Abstract A method and apparatus for generating an RF signal uses digital signal components to generate a synthesized RF signal having a plurality of frequency components. An analog filter is used to filter the synthesized RF signal. The analog filter is a tunable, active feedback circuit having one or more variable resonators and a variable gain block connected in a signal loop that is defined by a passband. The analog filter is tuned such that the passband of the analog filter overlaps one or more desired frequency components of the plurality of frequency components of the synthesized RF signal, and such that the passband has a relative bandwidth of about 1% or less. ## Claims ### Claim 1 A method of generating a signal, the method comprising the steps of: using digital signal components, generating a synthesized signal having a plurality of frequency components comprising a fundamental frequency component and a plurality of spurious frequency components; filtering the synthesized signal using an analog filter having a passband, the analog filter comprising a tunable, active feedback circuit having one or more variable resonators and a variable gain block connected in a signal loop; and tuning the analog filter such that the passband of the analog filter overlaps one or more desired frequency components of the plurality of spurious frequency components of the synthesized signal, and such that the passband has a relative bandwidth of about 1% or less. ### Claim 2 (depends on 1) The method of claim 1, further comprising the step of frequency translating the synthesized signal such that the plurality of frequency components comprises a plurality of translated frequency components. ### Claim 3 (depends on 2) The method of claim 2, further comprising the step of filtering the synthesized signal before the synthesized signal is frequency translated, after the synthesized signal is frequency translated, or both before and after the synthesized signal is frequency translated. ### Claim 4 (depends on 1) The method of claim 1, wherein the one or more desired frequency components are filtered from among frequency components that are as close as 0.01% to 0.1% of the one or more desired frequency components. ### Claim 5 (depends on 1) The method of claim 1, wherein the analog filter comprises a plurality of analog filters. ### Claim 6 (depends on 5) The method of claim 5, wherein the plurality of analog filters comprises a plurality of distinct passbands. ### Claim 7 (depends on 1) The method of claim 1, further comprising the steps of configuring the synthesized signal and tuning the analog filter to one or more different desired frequency components. ### Claim 8 An apparatus for generating a signal, the apparatus comprising: a synthesizer that generates a synthesized signal having a plurality of frequency components comprising a fundamental frequency component and a plurality of spurious frequency components; an analog filter connected to process the synthesized signal, the analog filter having a passband that filters the synthesized signal, the analog filter comprising a tunable, active feedback circuit having one or more variable resonators and a variable gain block connected in a signal loop; and a controller connected to the synthesizer and the analog filter, the controller comprising instructions to: tune the analog filter such that the passband of the analog filter overlaps one or more desired frequency components of the plurality of spurious frequency components, the analog filter being capable of generating a relative bandwidth of the passband of about 1% or less. ### Claim 9 (depends on 8) The apparatus of claim 8, further comprising a frequency translator adapted to translate the synthesized signal such that the plurality of frequency components comprises a plurality of translated frequency components. ### Claim 10 (depends on 9) The apparatus of claim 9, wherein the analog filter is connected between the synthesizer and the frequency translator, and further comprises an additional analog filter connected downstream of the frequency translator. ### Claim 11 (depends on 8) The apparatus of claim 8, wherein the one or more desired frequency components are filtered from among frequency components that are as close as about 0.1% to about 1% of the one or more desired frequency components. ### Claim 12 (depends on 8) The apparatus of claim 8, wherein the analog filter comprises a plurality of analog filters. ### Claim 13 (depends on 8) The apparatus of claim 8, wherein the synthesizer is adapted to tune the plurality of frequency components, and the controller further comprises instructions to tune the analog filter to a different one or more desired frequency components. ### Claim 14 (depends on 1) The method of claim 1, wherein tuning the analog filter further comprises adjusting the bandwidth of the passband. ### Claim 15 (depends on 8) The apparatus of claim 8, wherein tuning the analog filter further comprises adjusting the bandwidth of the passband.