JPH03276075A - Aliasing detecting device - Google Patents

Abstract

PURPOSE:To easily detect aliasing by providing a differentiating circuit, a comparator, and a counter, and obtaining a value for deciding whether or not the aliasing is caused by the counter when an analog input signal is sampled. CONSTITUTION:The differentiating circuit 1 outputs the differentiated value of the supplied analog input signal, a comparator 2 compares this differentiated signal with a zero level to obtain an output which is inverted into a high or low level when the differentiated signal crosses the zero level, and the counter 3 counts the frequency of respective edges of the comparison output. Its counted value corresponds to the appearance frequency of the peak of the analog input signal. The counter 3 is reset with a reset signal synchronized with a sampling clock. The counted value obtained by this constitution right before the counter is reset is used to decide whether or not the value is larger than the limit of sampling. Consequently, it can easily be decided whether or not the aliasing is caused.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a sampling aliasing detection device used in a digital oscilloscope or the like.

<Conventional technology> Conventionally, analog signals are sampled according to a sampling clock of a certain frequency, sequentially converted into digital signals and stored in a memory, and then the waveform data stored in the memory is read out and displayed on a display device such as a CRT. There is a digital oscilloscope that looks like this.

<Problems to be Solved by the Invention> By the way, this type of digital oscilloscope cannot detect aliasing when the frequency of the analog input signal exceeds the sampling frequency limit.

Additionally, when performing aliasing detection on waveforms such as television burst signals, there is a problem in that aliasing cannot be detected by simply connecting a counter and counting the number of times the input signal crosses an appropriate trigger level. .

The present invention has been made in view of these points, and an object thereof is to provide an aliasing detection device that can detect aliasing with a simple circuit configuration without going through a sampling process.

Means for Solving the Problems> To achieve such objects, the present invention includes a differentiating circuit that outputs a differential signal of a given analog input signal, and comparing the output of this differentiating circuit with a zero level, When the output of the differentiator circuit changes from negative to positive, it changes from LOW level to HI.
GH level, and a comparator that sends out an output that changes from HIGH level to LOW level when the output of the differentiating circuit changes from positive to negative; and a comparator that is reset by a reset signal synchronized with the sample clock, and the output of the comparator It is characterized by comprising a counter that counts the number of falling and rising edges.

In the present invention, an analog input signal is differentiated, and focusing on the fact that the differentiated signal becomes zero at the peak of the input signal, a comparator compares the differentiated signal with the zero level, and calculates the point at which the differentiated signal crosses the zero level. to obtain an output that is inverted to HIGH or LOW level. Then, the number of times each edge of this comparison output occurs is counted by a counter. The count value corresponds to the number of times the peak of the analog input signal appears.

The counter is reset by a reset signal synchronized with the sampling clock.

Based on the count value immediately before reset obtained by such a configuration, it is possible to easily determine whether aliasing occurs or not by determining whether the count value is greater than or less than the sampling limit.

<Example> The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an aliasing detection device according to the present invention. In the figure, 1 is the frequency f (
This is a differentiator circuit that outputs a signal of time differential molecule'(t) for an input signal of t). 2 is a comparator that compares the output of the differentiating circuit 1 with the zero level, and its output (binary signal) is LO when the output of the differentiating circuit 1 changes from negative to positive.
When the W level changes to HIGH level and the output of differentiator circuit 1 changes from positive to negative, it changes from HIGH level to LOW.
It changes depending on the level.

A counter 3 counts both edges of the output of the comparator 2, and the count value is reset by a reset signal synchronized with the sample clock.

The operation in such a configuration will be explained next.

An analog input signal having a frequency f (t) as shown in FIG. 2(a) is converted by the differentiating circuit 1 into a differential output f'(t) as shown in FIG. 2(b). Comparator 2 compares this output f' (t) with the zero level to determine whether it is positive or negative. The result is a signal as shown in FIG. 3(c). The edges of the output of comparator 2 (both edges) are the differential output f
'(t) crosses zero. Therefore, when the counter 3 counts these edges, the count value indicates the number of times the differential output f'(t) crosses zero, in other words, the number of peaks of the analog input signal f(t).

Counter 3 is reset by a signal synchronized with the sample clock, so by monitoring the value immediately before reset, it is possible to easily determine whether the number of peaks is greater or less than the sampling limit, and if it is, aliasing is detected. It can be determined that this occurs.

Note that, as the differentiating circuit 1, even if it does not perform substantially ideal differentiation as in the embodiment, a bypass filter having a cutoff frequency fc slightly lower than the frequency that causes aliasing may be used. Aliasing can be detected as well.

<Effects of the Invention> As explained in detail above, the present invention has the following effects.

In other words, conventional sampling oscilloscopes are unable to determine aliasing, or even if an aliasing determination device is available, the method is to count the number of times the input signal crosses Ov or an appropriate trigger level, so it is difficult to detect aliasing, such as a color burst signal on a television. However, if a part of the waveform causes aliasing, it cannot be determined unless that part is caught by the trigger level, but the apparatus of the present invention solves this problem.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an aliasing detection device according to the present invention, and FIG. 2 is an operation waveform diagram of each part. 1...Differential circuit 2...Comparator 3...Counter (c) Comparator output LOυ"LfLJ-+D

Claims (1)

[Claims] A differentiation circuit that outputs a differential signal of a given analog input signal, and a comparison that compares the output of this differentiation circuit with a zero level and sends out a binary signal according to the polarity of the output of the differentiation circuit. a counter that is reset by a reset signal synchronized with a sample clock and counts the number of falling and rising edges of the output of the comparator to determine whether aliasing occurs when sampling the analog input signal. An aliasing detection device characterized in that the aliasing detection device is configured such that a value for the aliasing is obtained from the counter.