JPH02254377A - Inspection of signal processor - Google Patents

Abstract

PURPOSE:To achieve a simplification of a construction and a reduction in inspection time by inputting a processing signal to be outputted with a cycle corresponding to a deviation of first and second frequencies into an inspector to perform an inspection. CONSTITUTION:When a sampling holding circuit 11 is mounted on an inspector 12, a first input signal Si (with a frequency fi) is generated from a first input signal generation circuit 13. A sample pulse Ss is generated from a sample pulse generation circuit 14. Moreover, as the circuit 11 performs a processing of sampling and holding the signal Si at a cycle of the pulse Ss with a frequency fs, a signal waveform is obtained as processing signal Ds. In other words, the signal Ds holds a level of the signal Si in a corresponding phase at each cycle of the pulse Ss and is turned to a signal with a frequency fi-fs as a whole. The signal Ds is cleared of a high frequency component with an LPF 15 and shaped to an inspection signal Sc to be inputted inspector section 16. This achieves a simplification of a construction and a reduction in inspection time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a testing method for testing a signal processing device such as a sample-and-hold circuit that samples and holds an analog input signal.

Conventional technology Conventionally, various image sensors and imaging devices use C.
A CD element (a charge-coupled element) is used. This CC
The output of the D element is processed by a sample and hold circuit (hereinafter referred to as S/H).
A so-called sample bold process is performed in which the signal is sampled at a predetermined sampling period and the level at that time is held. Currently, a single integrated circuit element is used as an S/H circuit that performs such processing.

Conventionally, when inspecting such a sample-and-hold circuit constructed as an integrated circuit element, a signal having a waveform similar to that of an actual CCD element output is generated and input as an input signal to be sampled and held. The frequency of such an input signal is, for example, 10 MHz, and a 10 MHz signal is also used as a sample pulse for determining the sampling period for sampling this input signal.

FIG. 3 is a block diagram showing the configuration of a conventional example for testing the S/H circuit 1. Connected to the S/H circuit 1 is an approximate waveform signal generation circuit 2 that generates a signal with an approximate waveform to the output of the COD element described above, and a sample pulse generation circuit 3 that generates sample pulses. Therefore, an output signal having a frequency of 10 MHz is also obtained from the S/H circuit 1, and this output signal is input to the testing device 4 to test the S/H circuit 1. Inspection items include output waveform distortion, frequency, and abnormal level.

These tests check whether the electrical characteristics of circuit elements such as capacitors included in the S/H circuit 1 that determine the waveform of the output signal and whether sample and hold operations are being performed properly.

Problems to be Solved by the Invention In the conventional inspection method as described above, it is necessary to generate a signal with a waveform similar to the actual COD output from the approximate waveform signal generating circuit 2 at, for example, 10 MHz. There is a problem that the configuration of 2 becomes complicated. In addition, the inspection device 4 has a 10M
It is necessary to have the ability to perform the above-mentioned inspection on an output signal of about Hz, and it is necessary to use an unnecessarily high-precision inspection device 4.
Therefore, the configuration of such an inspection device 4 becomes larger and the manufacturing cost of the S/H circuit 1 increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned technical problems and to provide a method for testing a signal processing device that has a simple configuration and can be easily tested.

Means for Solving the Problems In the present invention, a first input signal and a second input signal having a period are respectively input, and the first input signal is obtained by performing predetermined processing for each period of the second input signal. In an inspection method of inspecting a signal processing device that outputs a processed signal by inputting the processed signal into an inspection device, the first frequency has a first frequency and repeats a fixed waveform every period.
While inputting the input signal, inputting a second input signal having a frequency near the first frequency and having a second frequency other than a frequency that is an integral multiple of the first frequency, the first frequency and the second frequency are This is a method for testing a signal processing device, characterized in that testing is performed by inputting a processed signal outputted with a period corresponding to a deviation into the testing device.

According to the present invention, a first input signal and a second input signal are respectively input to the signal processing device to be inspected, and the first input signal is subjected to a predetermined process for each period of the second input signal. The processed signal is output. At this time, as the first input signal,
A signal having a first frequency and repeating a fixed waveform every cycle is input. Further, as the second input signal, a signal having a second frequency that is near the first frequency and other than a frequency that is an integral multiple of the first frequency is input.

Therefore, the processed signal output from the signal processing device is the result of performing the processing on the first input signal with different phases for each period of the second input signal. Therefore, this processed signal has a period corresponding to the deviation between the first frequency and the second frequency, and this period is significantly longer than the periods of the first input signal and the second input signal.

Therefore, the inspection equipment to which the processed signals are inputted only needs to perform the inspection on the processed signals having the relatively same cycle, which greatly reduces the inspection accuracy of the inspection equipment and enables short-time inspection using the inspection equipment with a simple configuration. It can be carried out. Further, the first input signal may be a signal that repeats a fixed waveform every cycle corresponding to the first frequency, and a configuration for generating such a signal can be constructed relatively easily. Therefore, in this respect as well, the configuration can be simplified and the inspection time can be shortened.

Embodiment FIG. 1 is a block diagram illustrating a configuration according to an embodiment of the present invention. This embodiment will be described with reference to FIG. 1. This embodiment will describe an output signal from a CCD element used in, for example, a contact image sensor for reading a document image in a facsimile machine or various imaging devices. The present invention relates to a method of testing a sample and hold circuit, which is a signal processing device that performs sample and hold. In performing such a test, the S/H circuit 11 is attached to the test device 12.

This inspection device 12 uses a signal having a waveform similar to the output signal from an actual CCD element as described in the prior art section as the first input signal SL to be processed that is supplied to the S/H circuit 11. Change the frequency f1 (for example, 10.IMHz
), and further includes a first input signal generating circuit 13 that generates a sine wave of frequency Ss (for example, 1
0MHz, duty 25% or less, fi≠n-8sin
is an integer, and Ss is in the vicinity of fi).

In addition, the inspection device 12 receives a processed signal DS obtained by subjecting the first input signal Si to sample-hold processing using a sample pulse Ss, and a low-pass filter (hereinafter abbreviated as LPF) 15 that removes high frequency components. ,LPF
An inspection section 16 inspects the waveform, frequency, amplitude, etc. of the output of the S/H circuit 15, and inspects abnormalities in electrical constants of each circuit element of the S/H circuit 11, overall malfunction of the S/H circuit 11, etc. and will be provided.

FIG. 2 is a waveform diagram illustrating the operation of this embodiment. Second
The operation of this embodiment will be described with reference to the drawings. When the S/H circuit 11 is attached to the inspection device 12, the first
The input signal generating circuit 13 generates and supplies a first input signal S1 as shown in FIG. 2(1). Further, the sample pulse generation circuit 14 generates and supplies a sample pulse Ss having the characteristics as described above, as shown in FIG. 2(2). Since the S/H circuit 11 performs sample and hold processing on the first input signal St at the period of the sample pulse Ss of the frequency fs, a signal waveform as shown in FIG. 2 (3) is obtained as the processed signal DS. It will be done.

That is, the processed signal DS holds the level of the first input signal S1 at the corresponding phase for each cycle of the sample pulse Ss, and becomes a signal having the frequency (fi-fs) as a whole. This processed signal DS has high frequency components removed by the LPF 15, is shaped into a test signal Sc as shown in FIG. 2 (4), and is input to the test section 16. Such a test signal S
According to the frequency example of this embodiment, the frequency of c is f i - f s = o, IMHz - (1>), and the S/H circuit 1 in the conventional inspection method described with reference to FIG. Although the frequency of the output signal from the sample pulse is the same as that of the sample pulse, it has a much lower frequency.

Therefore, such a comparatively low frequency test signal Sc
It is possible to simplify the configuration of the inspection section 16 that performs the inspection, and it is also possible to perform the inspection using a relatively simple inspection procedure. Furthermore, the first input signal generation circuit 13 generates a sine wave, and can be configured extremely simply compared to a circuit configuration that forms a waveform similar to the output waveform from an actual CCD element, as explained in the prior art section. It is something.

That is, according to this embodiment, the configuration for testing the S/H circuit 11 can be significantly simplified, and the time required for testing can be significantly shortened.

In the above embodiment, the signal processing device to be tested is an S/
Although the present invention has been described with reference to the H circuit 11, the present invention is not limited to such an S/H circuit 11, and the present invention is not limited to such an S/H circuit 11, and the present invention is not limited to such a S/H circuit 11. It is optionally implemented for the circuit in which it is applied.

Effects of the Invention As described above, according to the present invention, the processed signal output from the signal processing device is the result of processing the first input signal with different phases for each cycle of the second input signal. Therefore, this processed signal has a period corresponding to the deviation between the first frequency and the second frequency, and this period is significantly longer than the periods of the first input signal and the second input signal. Therefore, the inspection device to which the processed signal is inputted only needs to perform the inspection on the relatively long-cycle processed signal, and the inspection accuracy of the inspection device can be significantly reduced and an inspection device with a simple configuration can be used. Further, the first input signal may be a signal that repeats a fixed waveform every cycle corresponding to the first frequency, and a configuration for generating such a signal can be constructed relatively easily. Therefore, in this respect as well, the configuration can be simplified and the inspection time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram explaining the configuration according to one embodiment of the present invention, FIG. 2 is a waveform diagram explaining the operation of this embodiment, and FIG.
The figure is a block diagram illustrating the configuration of a typical conventional example. 11...878 circuits, 12...inspection equipment, 13...
- First input signal generation circuit, 14... Sample pulse generation circuit, 16... Inspection section, SL... First input signal,
Ss...sample pulse, DS...processed signal, Sc
...Inspection signal, fi, fs...frequency

Claims (1)

[Claims] A first input signal and a second input signal having a period are respectively input, and a processed signal obtained by performing predetermined processing on the first input signal for each period of the second input signal is output. In this method, a first input signal having a first frequency and repeating a fixed waveform every cycle is input, and the first input signal having a first frequency is A second input signal having a second frequency that is nearby and other than a frequency that is an integral multiple of the first frequency is input, and the second input signal is output with a period corresponding to the deviation between the first frequency and the second frequency. 1. A method for testing a signal processing device, comprising inputting a processed signal into the testing device to perform testing.