A method of frequency estimation. A clock output from a frequency synthesizer is received at an input of a ring encoder. The ring encoder generates outputs including a ring encoder output clock and an encoded output which represents LSBs of a clock cycle count of the clock output. A binary counter is run using the ring encoder output clock which provides an output count which represents MSBs of the clock cycle count. Using a reference clock, the encoded output is sampled to provide a sampled encoded output and the output count is sampled to provide a sampled output count. Error correcting is applied to the sampled encoded output to provide a corrected sampled encoded output. The corrected sampled encoded output and sampled output count are combined to provide a combined output which is used for estimating an instantaneous or average frequency of the clock output.

A signal inspection apparatus, a signal inspection system, a signal inspection method, and a non-transitory computer-readable medium encoded with a signal inspection program are provided, all of which can appropriately detect discrepancy between multiplexed signals. A signal inspection apparatus includes: an acquisition unit that acquires values of at least two signals among multiplexed signals in a predetermined cycle; a count unit that counts respective changes in the at least two signals in a predetermined time frame; a calculation unit that calculates a difference between the counts of changes; and an output unit that performs an output indicating discrepancy between the signals, if the difference between the counts of changes exceeds an allowable value.

A signal inspection apparatus, a signal inspection system, a signal inspection method, and a non-transitory computer-readable medium encoded with a signal inspection program are provided, all of which can appropriately detect discrepancy between multiplexed signals. A signal inspection apparatus includes: an acquisition unit that acquires values of at least two signals among multiplexed signals in a predetermined cycle; a count unit that counts respective changes in the at least two signals in a predetermined time frame; a calculation unit that calculates a difference between the counts of changes; and an output unit that performs an output indicating discrepancy between the signals, if the difference between the counts of changes exceeds an allowable value.

A frequency estimator for estimating a frequency, including a counter configured to count an integer number of full clock cycles during a measurement time window; a Time-to-Digital Converter (TDC) configured to measure a fraction of a clock cycle during the measurement time window; and a processor configured to determine the estimated frequency based on the counted number of full clock cycles and the measured fraction of the clock cycle.

A frequency measurement apparatus includes: a measurement period setting circuit that sets a measurement period based on a reference clock signal; a first counter circuit that counts the number of pulses of the reference clock signal in a period based on an input signal during the measurement period; a second counter circuit that counts the number of pulses of the input signal during the measurement period; a first frequency calculation circuit that calculates a first frequency; a second frequency calculation circuit that calculates a second frequency; and a frequency selection circuit that selects the first frequency or the second frequency as a frequency of the input signal.

A frequency measurement apparatus includes: a measurement period setting circuit that sets a measurement period based on a reference clock signal; a first counter circuit that counts the number of pulses of the reference clock signal in a period based on an input signal during the measurement period; a second counter circuit that counts the number of pulses of the input signal during the measurement period; a first frequency calculation circuit that calculates a first frequency; a second frequency calculation circuit that calculates a second frequency; and a frequency selection circuit that selects the first frequency or the second frequency as a frequency of the input signal.

The present invention discloses a waveform measuring method. It converts the waveform to be measured into two corresponding square waves by two comparators. When the hardware logic device receives the signal from the host computer software to start waveform acquisition, it acquires two square waves and simultaneously starts the counter to count with a fixed high frequency clock. When the waveform is flipped, if the count value is less than the set filter value, the waveform is filtered out; if the count value is greater than the set filter value, the hardware logic device saves the waveform and count value and clears the counter to zero. The number of waveform flips is judged whether the set value is reached, and if not, the count is recounted; if it is reached, the waveform acquisition is stopped, and then the waveform and count values saved by the hardware logic device are read and optimized by the host computer software. According to the test requirements, the corresponding algorithm is executed, and the calculation results are output. It improves the accuracy and precision of the measurement and increases the flexibility of the measuring method.

The present invention discloses a waveform measuring method. It converts the waveform to be measured into two corresponding square waves by two comparators. When the hardware logic device receives the signal from the host computer software to start waveform acquisition, it acquires two square waves and simultaneously starts the counter to count with a fixed high frequency clock. When the waveform is flipped, if the count value is less than the set filter value, the waveform is filtered out; if the count value is greater than the set filter value, the hardware logic device saves the waveform and count value and clears the counter to zero. The number of waveform flips is judged whether the set value is reached, and if not, the count is recounted; if it is reached, the waveform acquisition is stopped, and then the waveform and count values saved by the hardware logic device are read and optimized by the host computer software. According to the test requirements, the corresponding algorithm is executed, and the calculation results are output. It improves the accuracy and precision of the measurement and increases the flexibility of the measuring method.

A frequency measurement apparatus includes: a measurement period setting circuit that sets a measurement period based on a reference clock signal; a first counter circuit that counts the number of pulses of the reference clock signal in a period based on an input signal during the measurement period; a second counter circuit that counts the number of pulses of the input signal during the measurement period; a first frequency calculation circuit that calculates a first frequency; a second frequency calculation circuit that calculates a second frequency; and a frequency selection circuit that selects the first frequency or the second frequency as a frequency of the input signal.

A frequency measurement apparatus includes: a measurement period setting circuit that sets a measurement period based on a reference clock signal; a first counter circuit that counts the number of pulses of the reference clock signal in a period based on an input signal during the measurement period; a second counter circuit that counts the number of pulses of the input signal during the measurement period; a first frequency calculation circuit that calculates a first frequency; a second frequency calculation circuit that calculates a second frequency; and a frequency selection circuit that selects the first frequency or the second frequency as a frequency of the input signal.