# US 2021/0242860 A1 · Cycle accurate skew adjust > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0242860 A1 - Document ID: US20210242860A1 - Status: Published application - Kind: A1 - Application number: 16/776,764 - Filed: 2020-01-30 - Published: 2021-08-05 - Earliest claimed: 2020-01-30 - Assignees: International Business Machines Corporation - Applicants: International Business Machines Corporation - Inventors: Andreas H. A. Arp; Douglas J. Malone; Thomas Makowski; Michael V. Koch - Web page: https://patentgrep.com/patent/US20210242860A1 ## CPC - H03K 5/05: by the use of clock signals or other time reference signals - G06F 1/08: Clock generators with changeable or programmable clock frequency - G06F 1/10: Distribution of clock signals {, e.g. skew} - H03K 5/14: by the use of delay lines (H03K5/133 takes precedence) - H03L 7/08: Details of the phase-locked loop - 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) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - H03L: AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES (generation of oscillations H03B) ## Abstract A method for cycle accurate deskewing a second clock signal with respect to a first clock signal is provided. The first clock signal has been propagated from a first clock source through a first clock tree. The second clock signal has been propagated from the first clock source through a second clock tree. The second clock tree comprises a programmable delay line for inducing a delay. The method comprises determining a first clock tree latency of the first clock tree, determining a second clock tree latency of the second clock tree, setting a cycle time of the first clock source to a measuring cycle time depending on the first clock tree latency and/or the second clock tree latency, adjusting a skew between the second clock signal and the first clock signal, setting the cycle time of the first clock source to an operating cycle time. ## Claims ### Claim 1 A method for cycle accurate adjusting a skew between a second clock signal and a first clock signal, wherein the first clock signal has been propagated from a first clock source through a first clock tree, wherein the second clock signal has been propagated from the first clock source through a second clock tree, wherein the second clock tree comprises a programmable delay line operable for inducing a delay; wherein the method comprises determining a first clock tree latency of the first clock tree, determining a second clock tree latency of the second clock tree, setting a cycle time of the first clock source to a measuring cycle time depending on the first clock tree latency and/or the second clock tree latency, adjusting a skew between the second clock signal and the first clock signal, setting the cycle time of the first clock source to an operating cycle time. ### Claim 2 (depends on 1) The method according to claim 1, wherein adjusting a skew between the second clock signal and the first clock signal comprises measuring a skew between the second clock signal and the first clock signal and adjusting one of the first clock tree latency and the second clock tree latency based on the measured skew. ### Claim 3 (depends on 1) The method according to claim 1, wherein setting the cycle time of the first clock source to a measuring cycle time comprises setting the cycle time to a measuring cycle time which is equal or longer than the longer one of the first clock tree latency and the second clock tree latency. ### Claim 4 (depends on 1) The method according to claim 1, wherein determining the first clock tree latency of the first clock tree and/or the second clock tree latency of the second clock tree comprises determining the respective first clock tree latency and/or second clock tree latency based on a measurement. ### Claim 5 (depends on 1) The method according to claim 1, wherein determining the first clock tree latency of the first clock tree and/or the second clock tree latency of the second clock tree comprises determining the respective first clock tree latency and/or second clock tree latency based on a simulation. ### Claim 6 (depends on 5) The method according to claim 5, wherein determining the second clock tree latency of the second clock tree based on a measurement comprises measuring a control system response time of the second clock tree. ### Claim 7 (depends on 1) The method according to claim 1, wherein measuring a skew between the first clock signal and the second clock signal comprises using a skew sensor for measuring a quantitative skew between a second clock signal and a first clock signal, wherein the skew sensor comprises at least two skew detectors, wherein each skew detector is operable for detecting a skew between two input signals, wherein a first skew detector is operable for receiving either the first clock signal or the second clock signal as first input signal and the other one of the first clock signal and the second clock signal delayed by a first delay difference induced by one or more delay elements as second input signal, wherein a second skew detector is operable for receiving either the first clock signal or the second clock signal as first input signal and the other one of the first clock signal and the second clock signal optionally delayed by a second delay difference induced by one more delay elements, wherein the second delay difference is different from the first delay difference, as second input signal. ### Claim 8 A logic device for cycle accurate adjusting a skew between a second clock signal and a first clock signal, wherein the first clock signal has been propagated from a first clock source through a first clock tree, wherein the second clock signal has been propagated from the first clock source through a second clock tree, wherein the second clock tree comprises a programmable delay line operable for inducing a delay; wherein the logic device comprises a skew control unit is operable for determining a first clock tree latency of the first clock tree, determining a second clock tree latency of the second clock tree, setting a cycle time of the first clock source to a measuring cycle time depending on the first clock tree latency and/or the second clock tree latency, adjusting a skew between the second clock signal and the first clock signal, setting the cycle time of the first clock source to an operating cycle time. ### Claim 9 (depends on 8) The logic device according to claim 8, wherein adjusting a skew between the second clock signal and the first clock signal comprises measuring a skew between the second clock signal and the first clock signal and adjusting one of the first clock tree latency and the second clock tree latency based on the measured skew. ### Claim 10 (depends on 8) The logic device according to claim 8, wherein setting the cycle time of the first clock source to a measuring cycle time comprises setting the cycle time to a measuring cycle time which is equal or longer than the longer one of the first clock tree latency and the second clock tree latency. ### Claim 11 (depends on 8) The logic device according to claim 8, wherein setting the cycle time of the first clock source to a measuring cycle time comprises setting the cycle time to a measuring cycle time which is equal or longer than the average of the first clock tree latency and the second clock tree latency. ### Claim 12 (depends on 8) The logic device according to claim 8, wherein determining the first clock tree latency of the first clock tree comprises determining the first clock tree latency based on a measurement. ### Claim 13 (depends on 8) The logic device according to claim 8, wherein determining the first clock tree latency of the first clock tree comprises determining the first clock tree latency based on a simulation. ### Claim 14 (depends on 8) The logic device according to claim 8, wherein determining the second clock tree latency of the second clock tree comprises determining the second clock tree latency based on a measurement. ### Claim 15 (depends on 8) The logic device according to claim 8, wherein determining the second clock tree latency of the second clock tree comprises determining the second clock tree latency based on a simulation. ### Claim 16 (depends on 8) The logic device according to claim 8, wherein the first clock source comprises a phase locked loop (PLL) clock, wherein the PLL clock is swinging in phase with an external clock signal, wherein the logic device comprises a PLL bypassing circuit, wherein the skew control unit is operable for using the bypassing circuit for bypassing the PLL clock for increasing a cycle time of the first clock signal and the second clock signal. ### Claim 17 (depends on 8) The logic device according to claim 8, wherein the first clock source comprises a phase locked loop (PLL) clock, wherein the PLL clock is swinging in phase with an external clock signal, wherein the PLL clock is swinging at a frequency defined by a divider setting of the PLL clock, wherein the PLL clock is swinging at a frequency which is a rational multiple greater than one defined by a divider setting of the PPL clock of the frequency of the external clock signal, wherein the logic device comprises a PLL bypassing circuit, wherein the skew control unit is operable for changing a divider setting of the PPL clock for increasing or decreasing a cycle time of the first clock signal and the second clock signal. ### Claim 18 (depends on 8) The logic device according to claim 8, wherein the first clock source comprises a phase locked loop (PLL) clock and an adjustable frequency divider arranged, according to a signal flow, after the PLL clock, wherein the PLL clock is swinging at a frequency defined by a divider setting of the PLL clock, wherein the skew control unit is operable for adjusting a divider setting of the adjustable frequency divider. ### Claim 19 (depends on 8) The logic device according to claim 8, wherein the logic device comprises a counter operable to be clocked by one of the first clock signal and the second clock signal, wherein the skew control unit is operable for measuring a control system response time of the second clock tree and determining the second clock tree latency based on the control system response time, wherein measuring the control system response time of the second clock tree comprises measuring a skew between the second clock signal and the first clock signal and storing the skew, initiating a delay change of a delay induced by the programmable delay line and starting a time measurement, at least one iteration of measuring the skew between the second clock signal and the first clock signal; comparing the measured skew with the stored skew; based on the result of the comparison, stopping after a current iteration and stopping the time measurement, and wherein a result of the time measurement is the control system response time, wherein starting a time measurement comprises initializing and starting a counter, and wherein stopping a time measurement comprises stopping the counter. ### Claim 20 (depends on 8) The logic device according to claim 8, wherein the logic device further comprises a skew sensor comprising at least two skew detectors, wherein each skew detector is operable for detecting a skew between two input signals, wherein a first skew detector is operable for receiving either the first clock signal or the second clock signal as first input signal and the other one of the first clock signal and the second clock signal delayed by a first delay difference induced by one or more delay elements as second input signal, wherein a second skew detector is operable for receiving either the first clock signal or the second clock signal as first input signal and the other one of the first clock signal and the second clock signal optionally delayed by a second delay difference induced by one more delay elements, wherein the second delay difference is different from the first delay difference, as second input signal, and wherein the skew control unit is operable for measuring a skew between the first clock signal and the second clock signal using the skew sensor.