Digital Electronics: Principles, Devices and Applications

Troubleshooting Digital Circuits and Test Equipment 67916.14.1 Universal Counters – Functional ModesThe functions available with modern universal counters, other than measurement of an unknownfrequency, are time interval measurement, period, time interval average, totalize, frequency ratio A/B,phase A relative to B and pulse width.16.14.1.1 Time Interval MeasurementThis mode measures the time that elapses between the occurrence of two events. One of the events,called the start signal, is usually fed into one of the channels, while the other, called the stop signal,feeds the second channel. The resolution of measurement is typically 10 ns or better. A typicalapplication of this measurement mode is in determination of the propagation delay in logic circuits.Variations of this mode can be used to measure pulse width and rise/fall times.16.14.1.2 Time Interval AverageThis mode can be used to improve the measurement resolution in the time interval measurement modefor a given clock frequency. The resolution improves as the square root of the number of measurements.That is, an average of 100 measurements would give a 10-fold improvement in resolution.16.14.1.3 PeriodIn this mode, the time period of the input signal is measured by counting clock pulses between twosuccessive leading or trailing edges of the input signal. Again, the period average function can be usedto improve upon the measurement resolution for a given clock. For instance, if the measurement weredone for 100 periods instead of one period for a given clock frequency, the measurement resolutionwould also improve by a factor of 100.16.14.1.4 TotalizeThe totalize mode gives a cumulative count of events over a known time period.16.14.1.5 Frequency Ratio A/BThis gives the ratio of the frequencies of signals fed to the A and B channels. This feature can be usedto test the performance of prescalers and frequency multipliers.16.14.1.6 Phase A Relative to BThis compares the phase delay between signals with similar frequencies.16.14.2 Basic Counter ArchitectureFigure 16.21 shows the architecture of a frequency counter when it is being used in the frequencymeasurement mode. The oscillator section, comprising a crystal-based oscillator and a frequency divider