# US 11,451,367 B1 · Techniques for enhanced clock recovery > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,451,367 B1 - Document ID: US11451367B1 - Status: Granted - Kind: B1 - Application number: 17/484,532 - Filed: 2021-09-24 - Published: 2022-09-15 - Granted: 2022-09-20 - Earliest claimed: 2021-03-12 - Assignees: Ciena Corporation - Applicants: Shahab Oveis Gharan; James St. Leger Harley; Tung Trong Nguyen - Inventors: Shahab Oveis Gharan; James St. Leger Harley; Tung Trong Nguyen - Web page: https://patentgrep.com/patent/US11451367B1 ## CPC - H04L 7/0079: {Receiver details} - H04B 10/6165: {Estimation of the phase of the received optical signal, phase error estimation or phase error correction} - H04L 7/02: Speed or phase control by the received code signals, the signals containing no special synchronisation information {(H04L7/0075 takes precedence)} - H04L 25/03012: {operating in the time domain (H04L25/03165, H04L25/03178 take precedence)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04B: TRANSMISSION ## Abstract A receiver generates a stream of digital samples from an analog electrical signal that represents data conveyed to the receiver over a communication channel, where the stream of digital samples comprises current samples corresponding to a current timepoint, previous samples corresponding to a timepoint earlier than the current timepoint, and subsequent samples corresponding to a timepoint later than the current timepoint. The receiver generates previous, current, and subsequent phase offset signals based on the previous, current, and subsequent samples, respectively. The receiver uses the previous phase offset signal to adjust clock frequency and clock phase of the current samples, thereby resulting in current adjusted samples. The receiver adjusts clock phase of the current adjusted samples based on any one of the previous, current, and subsequent phase offset signals. In some examples, receiver adjusts the clock phase of the current adjusted samples based on the subsequent phase offset signal. ## Claims ### Claim 1 A receiver apparatus comprising: circuitry configured to generate a stream of digital samples from an analog electrical signal, wherein the analog electrical signal is representative of data conveyed to the receiver apparatus over a communication channel, wherein the stream of digital samples comprises current digital samples corresponding to a current timepoint, previous digital samples corresponding to a timepoint earlier than the current timepoint, and subsequent digital samples corresponding to a timepoint later than the current timepoint; circuitry configured to generate previous, current, and subsequent phase offset signals based on the previous, current, and subsequent digital samples, respectively; circuitry configured to use the previous phase offset signal to adjust clock frequency and clock phase of the current digital samples, thereby resulting in current adjusted samples; and circuitry configured to adjust clock phase of the current adjusted samples based on any one of the previous, current, and subsequent phase offset signals. ### Claim 2 (depends on 1) The receiver apparatus as claimed in claim 1, wherein the timing of the current adjusted samples is adjusted based on the subsequent phase offset signal. ### Claim 3 (depends on 1) The receiver apparatus as claimed in claim 1, further comprising circuitry configured to generate previous, current, and subsequent compensated samples from the previous, current, and subsequent digital samples, respectively, wherein the previous, current, and subsequent compensated samples are at least partially compensated for chromatic dispersion in the communication channel, and wherein the previous, current, and subsequent phase offset signals are generated using the previous, current, and subsequent compensated samples, respectively. ### Claim 4 (depends on 1) The receiver apparatus as claimed in claim 1, further comprising circuitry configured to suppress tones in the current phase offset signal prior to using the current phase offset signal to adjust the phase of the previous digital samples, wherein the tones are associated with one or more fundamental frequencies. ### Claim 5 (depends on 4) The receiver apparatus as claimed in claim 4, wherein the current phase offset signal comprises first tones originating from the receiver at one of the fundamental frequencies, and wherein the current phase offset signal comprises second tones originating from outside the receiver at another one of the fundamental frequencies. ### Claim 6 (depends on 1) The receiver apparatus as claimed in claim 1, further comprising circuitry configured to apply a lowpass filter to the current phase offset signal to generate a filtered current phase offset signal; circuitry configured to calculate a first difference signal by subtracting the filtered current phase offset signal from the previous phase offset signal; and circuitry configured to adjust the clock phase of the previous digital samples based on the first difference signal. ### Claim 7 (depends on 5) The receiver apparatus as claimed in claim 5, further comprising circuitry configured to apply a notch filter to the first difference signal, thereby generating a notched difference signal; circuitry configured to calculate a second difference signal by subtracting the notched difference signal from the previous phase offset signal; and circuitry configured to adjust the clock phase of the previous digital samples based on the second difference signal. ### Claim 8 (depends on 7) The receiver apparatus as claimed in claim 7, wherein the notch filter comprises a comb filter configured to suppress harmonics of one or more fundamental frequencies. ### Claim 9 (depends on 1) The receiver apparatus as claimed in claim 1, further comprising circuitry configured to buffer the previous digital samples for a period of time prior to adjusting the clock phase of the previous digital samples based on the current phase offset signal. ### Claim 10 (depends on 9) The receiver apparatus as claimed in claim 9, wherein the period of time matches a sum of a first time delay associated with generating the current phase offset signal based on the current digital samples, and a second time delay associated with applying a lowpass filter to the current phase offset signal. ### Claim 11 A method comprising: generating a stream of digital samples from an analog electrical signal, wherein the analog electrical signal is representative of data conveyed to a receiver apparatus over a communication channel, wherein the stream of digital samples comprises current digital samples corresponding to a current timepoint, previous digital samples corresponding to a timepoint earlier than the current timepoint, and subsequent digital samples corresponding to a timepoint later than the current timepoint; generating previous, current, and subsequent phase offset signals based on the previous, current, and subsequent digital samples, respectively; using the previous phase offset signal to adjust clock frequency and clock phase of the current digital samples, thereby resulting in current adjusted samples; and adjusting clock phase of the current adjusted samples based on any one of the previous, current, and subsequent phase offset signals. ### Claim 12 (depends on 11) The method as claimed in claim 11, wherein the clock phase of the current adjusted samples is adjusted based on the subsequent phase offset signal. ### Claim 13 (depends on 11) The method as claimed in claim 11, further comprising generating previous, current, and subsequent compensated samples from the previous, current, and subsequent digital samples, respectively, wherein the previous, current, and subsequent compensated samples are at least partially compensated for chromatic dispersion in the communication channel, and wherein the previous, current, and subsequent phase offset signals are generated using the previous, current, and subsequent compensated samples, respectively. ### Claim 14 (depends on 11) The method as claimed in claim 11, further comprising suppressing tones in the current phase offset signal prior to using the current phase offset signal to adjust the clock phase of the previous digital samples, wherein the tones are associated with one or more fundamental frequencies. ### Claim 15 (depends on 14) The method as claimed in claim 14, wherein the current phase offset signal comprises first tones originating from the receiver at one of the fundamental frequencies, and wherein the current phase offset signal comprises second tones originating from outside the receiver at another one of the fundamental frequencies. ### Claim 16 (depends on 11) The method as claimed in claim 11, further comprising applying a lowpass filter to the current phase offset signal to generate a filtered current phase offset signal; calculating a first difference signal by subtracting the filtered current phase offset signal from the previous phase offset signal; and adjusting the clock phase of the previous digital samples based on the first difference signal. ### Claim 17 (depends on 15) The method as claimed in claim 15, further comprising applying a notch filter to the first difference signal, thereby generating a notched difference signal; calculating a second difference signal by subtracting the notched difference signal from the previous phase offset signal; and adjusting the clock phase of the previous digital samples based on the second difference signal. ### Claim 18 (depends on 17) The method as claimed in claim 17, wherein the notch filter comprises a comb filter configured to suppress harmonics of one or more fundamental frequencies. ### Claim 19 (depends on 11) The method as claimed in claim 11, further comprising buffering the previous digital samples for a period of time prior to adjusting the clock phase of the previous digital samples based on the current phase offset signal. ### Claim 20 (depends on 19) The method as claimed in claim 19, wherein the period of time matches a sum of a first time delay associated with generating the current phase offset signal based on the current digital samples, and a second time delay associated with applying a lowpass filter to the current phase offset signal.