The frequency counter function is designed according to its application. The most common application of frequency counters is to determine the characteristics of transmitters and receivers. The frequency of the transmitter must be verified and calibrated in order to meet the requirements of the relevant rules and regulations. The frequency counter measures the output frequency and some key internal frequency points.
Today, with the rapid development of test technology, the frequency counter function is constantly improving and enriching to meet the needs of different test fields. Faced with instruments with different functions and specifications, engineers need to choose the instrument that meets their needs according to their own needs, so as to bring maximum efficiency to the test work.
SYN5636 high-precision general-purpose counterOn the basis of foreign countries, the measurement functions of time interval, pulse width, rise time, fall time, duty cycle, phase and so on are newly added, and there are powerful mathematical and statistical functions, including average, standard deviation, maximum, minimum, peak-to-peak, cumulative counting, Allan variance, frequency deviation, instantaneous diurnal deviation, trend chart and histogram and other functions.
The earliest frequency counters were designed to count certain things that needed to be counted. Before the invention of counters, frequency measurements were done with frequency meters. Frequency counters were one of the first instruments to digitally perform precise measurements of signal parameters.
The main indicators of the frequency counter are the measurement range, measurement function, accuracy and stability, which are also the main basis for determining the high and low. With the development of electronic testing technology, frequency counters are becoming more and more mature. At present, frequency counters can easily measure signals in RF and microwave bands. In addition to frequency measurements, most frequency counters combine the following functions: frequency ratio, time interval, period, rise and fall time, phase, duty cycle, positive and negative pulse width, sum, peak voltage, and time interval averaging. The highest level of frequency meter function extension is the integration of the functions of a modulation domain analyzer.
SYN5636 high-precision general-purpose counter
In this article, starting from the basic functions of frequency counters, the measurement parameters are introduced:
Frequency counter measurement function
1. Frequency measurement.
Frequency represents the number of times a waveform vibrates per unit time, is the reciprocal of the period, and frequency is the most basic measurement parameter.
According to the different frequency ranges, frequency counters can be divided into two categories: general-purpose frequency counters and microwave frequency counters. The measurement range of the former is generally below 1GHz; Microwave frequency counters provide high-performance frequency measurements from DC to 10GHz, covering the entire RF and microwave frequency bands. High-frequency measurement is a unique advantage of frequency counters, which is difficult to achieve with ordinary oscilloscopes. Frequency measurement is very simple, connect the signal to the frequency counter input, and then adjust the function key to the frequency measurement, and the current frequency value will be displayed on the screen. Only one input channel is required for a single frequency measurement.
2. Cycle (t).
The period is the time it takes for the waveform to vibrate once, which is the reciprocal of the frequency, and most frequency counters provide this function. The measurement of the signal period is basically similar to the frequency measurement.
SYN5636 high-precision general-purpose counter
3. Frequency ratio (f1 f2).
The frequency ratio is a comparison of two frequencies and can be used to test the performance of a frequency multiplier or a pre-displacement calculator (divider). In many instrument systems, the ratio of two frequencies is much more meaningful than two independent frequency values. For example, in the development of ratiometric capacitive sensors, engineers are concerned with the frequency ratio of the two signals. In this case, the frequency counter frequency ratio function can be used to display the frequency ratio of the two input signals intuitively and quickly. It eliminates the inconvenience of measuring the frequency of two signals and then calculating it by itself. This feature requires the frequency counter to have at least two channels. If there are three input signals, the frequency ratio of any two signals can be measured.
4. Time interval.
The time interval measures the time elapsed between the start signal and the end signal. As shown in Figure 3, the start signal is typically fed into one channel A, while the end signal is typically fed into the other channel B, a feature often referred to as world interval A to B. Measurements are typically made with a resolution of 100 ns or better, sometimes down to the picosecond (10-12) level.
High-resolution time interval measurement plays a very important role in the fields of time and frequency transmission and measurement, aerospace, radar positioning, laser ranging, etc. This feature also requires the frequency counter to have at least two channels.
5. Phase difference.
Phase difference, also known as phase shift, refers to the difference between the phases of two signals with equal frequencies, indicating the time advance or lag relationship between the two signals.
6. Rise and fall time.
The rise time is usually defined as the time it takes for a signal to go from 10 to 90 of its steady-state maximum, and similarly, the fall time corresponds to the time it takes for the signal to go from 90 to 10 of its steady-state maximum. Rise, fall time, and pulse duration are particularly useful in digital circuit measurements. If the trigger points for the rise and fall times are known, the slew rate (v s) calculation can be displayed based on the measured rise and fall times.
7. Pulse width.
Pulse width, pulse amplitude, and pulse shape are the main parameters of a pulse signal. The pulse width is usually the time difference between the two points before and after the pulse amplitude of 50. As shown in Figure 3, the pulse width is used to indicate the duration of the pulse energy action. Frequency counters are generally capable of measuring positive and negative pulse widths.
8. Duty cycle.
Duty cycle is the ratio of the time that the signal is high or low to the total time of the signal, and can also be expressed as the proportion of a single pulse width to the period. In Figure 3, the ratio of the width of the positive pulse to the period is 42, which is the duty cycle of 42. The duty cycle of a square wave signal is 50. All other things being equal, the larger the duty cycle, the higher the energy carried by the signal.
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9. Cumulative statistics.
Accumulation is a simple count of events. It is useful for electronic or physical event counting or automated testing where digitized results are required. The counter adds up and displays the number of events while the gate circuit is turned on. In some cases, this feature is called cumulative counting.
10. Time interval measurement function.
Time interval measurement is the measurement of the time difference between a particular "start" event and an "end" event. Time interval measurements can be used to measure circuit delays, radar pulse intervals, particle flight times, cable lengths, pulse periods, pulse widths, rise times, phase differences, and more.
11. Edge test function.
When a signal changes, we often need to detect that change as a trigger for other events. According to the clock domain to which the detected signal belongs, edge detection can be divided into synchronous edge detection and asynchronous synchronous detection. Synchronous edge detection means that the input signal comes from the same clock domain; Asynchronous edge detection is when the input signal comes from a different clock domain.
Frequency counter application
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