A virtual critical path (VCP) circuit is defined separate from an actual critical path circuit. The VCP operates in accordance with a special clock signal. The actual critical path circuit operates in accordance with a system clock signal. The VCP circuit has a signal timing characteristic substantially equal to that of the actual critical path circuit. The VCP circuit includes computational circuitry defined to compute an output value based on an input value, and comparison circuitry defined to compare the output value with an expected result value. A match between the output value computed by the VCP circuit and the expected result value indicates that a frequency of the special clock signal is acceptable. The VCP circuit is used to determine a maximum acceptable frequency of the special clock signal. A frequency of the system clock signal is then set to the maximum acceptable frequency of the special clock signal.

A clock generator circuit includes: first to N.sup.th nodes, where N is an even number equal to or greater than 2; and a parallel-to-serial conversion circuit suitable for parallel-to-serial converting signals of the first to N.sup.th nodes to output a clock through an output node, wherein, in an activation section of the clock, the signals of even-numbered nodes among the first to N.sup.th nodes have a first level, and the signals of odd-numbered nodes among the first to N.sup.th nodes have a second level which is different from the first level, and wherein, in a deactivation section of the clock, the signals of the first to N.sup.th nodes have the same level.

A clock generator circuit includes: first to N.sup.th nodes, where N is an even number equal to or greater than 2; and a parallel-to-serial conversion circuit suitable for parallel-to-serial converting signals of the first to N.sup.th nodes to output a clock through an output node, wherein, in an activation section of the clock, the signals of even-numbered nodes among the first to N.sup.th nodes have a first level, and the signals of odd-numbered nodes among the first to N.sup.th nodes have a second level which is different from the first level, and wherein, in a deactivation section of the clock, the signals of the first to N.sup.th nodes have the same level.

Systems, methods, and circuitries are provided to generate a radio frequency (RF) signal having a desired radio frequency f.sub.RF. In one example a frequency synthesizer system includes a clock, an opportunistic phase locked loop (PLL), and an RF PLL. The clock circuitry is configured to generate a clock signal having a frequency f.sub.XTL. The opportunistic phase locked loop (PLL) is configured to generate a reference signal having a reference frequency f.sub.REF that is close to a free-running frequency of an oscillator in the opportunistic PLL. The opportunistic PLL is configured to synchronize the reference signal to the clock signal. The RF PLL is configured to generate the RF signal having the desired radio frequency and to synchronize the RF signal with the reference signal.

A delay circuit includes a coarse delay circuit, a header circuit, and a phase mixing circuit. The coarse delay circuit is configured to delay a reference clock signal to generate a first clock signal and a second clock signal and to change each phase of the first clock signal and the second clock signal by double a unit phase. The header circuit is configured to receive the first clock signal and the second clock signal and to generate a first phase clock signal and a second phase clock signal, between which a phase difference corresponds to half of the unit phase. The phase mixing circuit is configured to mix phases of the first phase clock signal and the second phase clock signal to generate an output clock signal.

A delay circuit includes a coarse delay circuit, a header circuit, and a phase mixing circuit. The coarse delay circuit is configured to delay a reference clock signal to generate a first clock signal and a second clock signal and to change each phase of the first clock signal and the second clock signal by double a unit phase. The header circuit is configured to receive the first clock signal and the second clock signal and to generate a first phase clock signal and a second phase clock signal, between which a phase difference corresponds to half of the unit phase. The phase mixing circuit is configured to mix phases of the first phase clock signal and the second phase clock signal to generate an output clock signal.

An object detection system for autonomous vehicle, comprising a radar unit and at least one ultra-low phase noise frequency synthesizer, is provided. The radar unit configured for detecting the presence and characteristics of one or more objects in various directions. The radar unit may include a transmitter for transmitting at least one radio signal; and a receiver for receiving the at least one radio signal returned from the one or more objects. The ultra-low phase noise frequency synthesizer may utilize Clocking device, Sampling Reference PLL, at least one fixed frequency divider, DDS and main PLL to reduce phase noise from the returned radio signal. This proposed system overcomes deficiencies of current generation state of the art Radar Systems by providing much lower level of phase noise which would result in improved performance of the radar system in terms of target detection, characterization etc. Further, a method or autonomous vehicle is also disclosed.

An object detection system for autonomous vehicle, comprising a radar unit and at least one ultra-low phase noise frequency synthesizer, is provided. The radar unit configured for detecting the presence and characteristics of one or more objects in various directions. The radar unit may include a transmitter for transmitting at least one radio signal; and a receiver for receiving the at least one radio signal returned from the one or more objects. The ultra-low phase noise frequency synthesizer may utilize Clocking device, Sampling Reference PLL, at least one fixed frequency divider, DDS and main PLL to reduce phase noise from the returned radio signal. This proposed system overcomes deficiencies of current generation state of the art Radar Systems by providing much lower level of phase noise which would result in improved performance of the radar system in terms of target detection, characterization etc. Further, a method or autonomous vehicle is also disclosed.

The Direct Synchronization of Synthesized Clock (DSSC) contributes a method, system and apparatus for reliable and inexpensive synthesis of inherently stable local clock synchronized to a referencing signal received from an external source. Such local clock can be synchronized to a referencing frame or a data signal received from wireless or wired communication link and can be utilized for synchronizing local data transmitter or data receiver. Such DSSC can be particularly useful in OFDM systems such as LTE/WiMAX/WiFI or Powerline/ADSL/VDSL, since it can secure lower power consumption, better noise immunity and much more reliable and faster receiver tuning than those enabled by conventional solutions.

The Direct Synchronization of Synthesized Clock (DSSC) contributes a method, system and apparatus for reliable and inexpensive synthesis of inherently stable local clock synchronized to a referencing signal received from an external source. Such local clock can be synchronized to a referencing frame or a data signal received from wireless or wired communication link and can be utilized for synchronizing local data transmitter or data receiver. Such DSSC can be particularly useful in OFDM systems such as LTE/WiMAX/WiFI or Powerline/ADSL/VDSL, since it can secure lower power consumption, better noise immunity and much more reliable and faster receiver tuning than those enabled by conventional solutions.