A noise injection test system and a signal calibration method

Abstract

The present invention discloses a noise injection test system and a signal calibration method, comprising: a power input module connected to a signal injection module, the power input module is used to input a power signal to a signal superposition injection module; a noise input module is connected to a signal superposition injection module, the noise input module is used to input a noise signal to the signal superposition injection module; a control setting compensation module is connected to the noise input module, the control setting compensation module is used to control the frequency band of the noise signal output by the noise input module and determine the amplitude compensation amount of the noise signal; the signal injection module receives the noise signal and the power signal, and generates a superposition signal; a test module is connected to the signal injection module, the test module is used to receive a mixed signal power supply with superposition of noise, and output the data and waveform diagram of the superposition signal. The present invention belongs to the field of input noise. Accurate mixed waveforms and data can be obtained by using the system and calibration method provided by the present invention.

Description

Technical Field

[0001] The invention relates to the field of noise injection, and in particular to a noise injection test system and a signal calibration method. Background Art

[0002] The application fields of noise injection devices are quite wide, including but not limited to: in the electronics and communications industry, noise injection devices are used to test the anti-interference ability of circuit boards, evaluate the electromagnetic compatibility (EMC) of communication equipment, and verify the signal integrity of equipment.

[0003] The power signal is usually a DC or low-frequency AC signal with a large amplitude, while the noise signal may be very weak and high-frequency. It is a challenge to accurately capture these two signals with very different dynamic ranges on the same device at the same time. After the power signal and the noise signal are output, the signal will be attenuated, making it difficult to accurately obtain the superimposed signal. Therefore, it is urgent to propose a noise injection test system and a signal calibration method. Summary of the invention

[0004] The present invention solves the technical problem that it is difficult to obtain accurate superimposed signals and the load capacity is weak in the prior art by providing a noise injection test system and a signal calibration method, and achieves the technical effect of being able to accurately obtain superimposed signals and improve the load capacity.

[0005] In a first aspect, the present invention provides a noise injection test system, the system comprising a power input module, a noise input module, a control setting compensation module, a signal injection module and a test module, the test module comprising a device to be tested and an evaluation board;

[0006] The power input module is connected to the signal injection module, and the power input module is used to input a power signal to the signal injection module;

[0007] The noise input module is connected to the signal injection module, and the noise input module is used to input a noise signal to the signal injection module;

[0008] The control setting compensation module is connected to the noise input module, and is used to control the frequency band of the noise signal output by the noise input module and determine the amplitude compensation amount of the noise signal. The control setting compensation module is also used to determine the DC component and amplitude compensation amount of the power supply signal;

[0009] The signal injection module receives the noise signal and the power signal and generates a mixed power supply with a superimposed noise signal;

[0010] The test module is connected to the signal injection module, and is used for receiving a mixed power source with a superimposed noise signal, and outputting a mixed waveform diagram and test data.

[0011] Furthermore, the control setting compensation module is used to determine the amplitude compensation amount of the noise signal, including:

[0012] The control setting compensation module determines the amplitude compensation amount of the noise signal at the preset frequency according to the rated power of the test module, the preset target amplitude of the noise signal, and the preset frequency of the noise signal.

[0013] Further, including:

[0014] The power input module includes a power adapter or a programmable power supply.

[0015] Further, including:

[0016] The noise input module includes an oscilloscope or an arbitrary waveform generator.

[0017] Further, including:

[0018] The frequency band of the noise signal ranges from 10Hz to 10MHz.

[0019] In a second aspect, the present invention provides a signal calibration method, the method comprising:

[0020] Get the rated power of the device under test;

[0021] According to the rated power of the device to be tested, the preset frequencies of the noise signals and the preset amplitudes of the noise signals, the compensation amplitudes of the noise signals are obtained, wherein the preset frequencies of the noise signals correspond to the compensation amplitudes of the noise signals one by one;

[0022] According to the rated power of the device to be tested, the preset frequencies of the plurality of power signals and the preset amplitudes of the power signals, the compensation amplitudes of the plurality of power signals are obtained, wherein the preset frequencies of the power signals correspond to the compensation amplitudes of the power signals one by one;

[0023] Determining a target preset frequency and a preset amplitude of a power signal, and a target preset frequency and a preset amplitude of a noise signal;

[0024] According to the target preset frequency and preset amplitude of the power signal and the target preset amplitude and preset amplitude of the noise signal, a target superimposed signal and a waveform diagram corresponding to the target superimposed signal are obtained.

[0025] Further, according to the target preset frequency and preset amplitude of the power signal and the target preset amplitude and preset amplitude of the noise signal, a target superposition signal is obtained, including:

[0026] Determining a target compensation amplitude of the power signal corresponding to the target preset frequency of the power signal according to the target preset frequency and the preset amplitude of the power signal;

[0027] Determining a target compensation amplitude of the noise signal corresponding to the target preset frequency of the noise signal according to the target preset frequency and preset amplitude of the noise signal;

[0028] A target superposition signal is obtained according to a target compensation amplitude of the noise signal and a target compensation amplitude of the power supply signal.

[0029] Furthermore, according to the rated power of the device to be tested, the preset frequencies of the noise signals and the preset amplitudes of the noise signals, the compensation amplitudes of the noise signals are obtained, including:

[0030] According to the rated power of the device to be tested and the preset frequency of the noise signal, an actual output amplitude of the noise signal at the preset frequency is obtained;

[0031] Continuously adjusting the compensation amplitude of the noise signal, when the difference between the actual output amplitude of the noise signal at the preset frequency and the preset amplitude of the noise signal is less than a preset threshold, obtaining the compensation amplitude of the noise signal corresponding to the preset frequency of the noise signal;

[0032] A noise signal amplitude compensation table is constructed according to the preset frequencies of the plurality of noise signals and the compensation amplitudes of the plurality of noise signals.

[0033] Furthermore, according to the rated power of the device to be tested, the preset frequencies of the plurality of power signals, and the preset amplitudes of the power signals, the compensation amplitudes of the plurality of power signals are obtained, including:

[0034] According to the rated power of the device to be tested and the preset frequency of the power signal, an actual output amplitude of the power signal at the preset frequency is obtained;

[0035] Continuously adjusting the compensation amplitude of the power signal, when the difference between the actual output amplitude at the preset frequency of the power signal and the preset amplitude of the power signal is less than a preset threshold, obtaining the compensation amplitude of the power signal corresponding to the preset frequency of the power signal;

[0036] A power signal amplitude compensation table is constructed according to the preset frequencies of the plurality of power signals and the compensation amplitudes of the plurality of power signals.

[0037] Further, including:

[0038] The power signal is a triangle wave and is used to test the voltage tolerance;

[0039] The noise signal is a sine wave and is used to test the noise margin.

[0040] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0041] A noise injection test system and a signal calibration method proposed in the present invention can independently complete the signal power output of any DC component, frequency and amplitude, support the output of multiple noise signals, complete the superposition of noise signals with different amplitudes and frequencies, obtain accurate test data and mixed waveforms, and realize one-key automatic testing. Through this test method and device, the test results fully meet the test indicators of the relevant optical communication protocol, showing the effectiveness and feasibility of our scheme in ensuring signal quality. The implementation method of the present invention is simple, low-cost, and highly integrated, and various combinations of DC power supply and noise signal superposition settings can be adjusted according to actual needs to achieve the test requirements for specific communication protocols. Using the method provided by the present invention, an accurate and reliable superposition signal is obtained by linearly calibrating and compensating the signal attenuation on the superposition circuit. The present invention combines the programmable adjustable characteristics of the hardware circuit with the automated testing scheme of the host computer to build an efficient test system. The present invention solves the limitation that ordinary line injectors on the market are superpositions of specific waveform combinations, and provides a more flexible and diversified signal superposition scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 A schematic diagram of the structure of a noise injection test system provided by the present invention;

[0044] Figure 2 A schematic flow chart of a signal calibration method provided by the present invention;

[0045] Figure 3 The present invention provides a schematic diagram of waveforms before and after superposition.

[0046] Reference numerals

[0047] 1- Power input module, 2- Noise input module, 3- Control setting compensation module, 4- Signal injection module, 5- Test module, 6- Equipment to be tested, 7- Evaluation board. DETAILED DESCRIPTION

[0048] The embodiment of the present invention solves the technical problems in the prior art that it is difficult to obtain an accurate superposition signal and the carrying capacity is weak by providing a signal calibration method.

[0049] The technical solution of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0050] A signal calibration method, the method comprising: obtaining the rated power of a device to be tested; obtaining compensation amplitudes of several noise signals according to the rated power of the device to be tested, preset frequencies of several noise signals and preset amplitudes of the noise signals, wherein the preset frequencies of the noise signals correspond to the compensation amplitudes of the noise signals one-to-one; obtaining compensation amplitudes of several power signals according to the rated power of the device to be tested, preset frequencies of several power signals and preset amplitudes of the power signals, wherein the preset frequencies of the power signals correspond to the compensation amplitudes of the power signals one-to-one; determining a target preset frequency of the power signal and a target preset amplitude of the noise signal; obtaining a target superimposed signal and a waveform corresponding to the target superimposed signal according to the target preset frequency and preset amplitude of the power signal and the target preset amplitude and preset amplitude of the noise signal. In order to better understand the above technical scheme, the above technical scheme will be described in detail below in conjunction with the drawings in the specification and specific implementation methods.

[0051] First of all, the term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0052] The present invention provides Figure 1 A noise injection test system is shown, the system includes a power input module 1, a noise input module 2, a control setting compensation module 3, a signal injection module 4 and a test module 5, the test module 5 includes a device to be tested 6 and an evaluation board 7, wherein the evaluation board 7 is externally connected to the device to be tested 6.

[0053] The power input module 1 includes a programmable power supply or a 12V adapter. The power input module 1 is connected to the signal injection module 4, and the power input module 1 is used to input a power signal to the signal injection module 4. The noise injection test system can be powered by a power adapter or a programmable power supply.

[0054] Programmable Power Supply is a power supply device that can control the output voltage and current through external signals or commands. Programmable power supply usually has an interface that allows users to send commands through a computer or other control system to set output parameters, such as voltage, current upper and lower limits, ramp rate, on / off status, etc.

[0055] A power adapter is a power conversion device that is mainly used to convert alternating current (AC) into direct current (DC) and output a fixed DC voltage value.

[0056] The noise input module 2 is connected to the signal injection module 4, and the noise input module 2 is used to input a noise signal to the signal injection module 4. The noise input module 2 includes an oscilloscope or an arbitrary waveform generator. When an oscilloscope is used, it can be externally connected to the signal injection module 4 through a banana head power cord; when a built-in arbitrary waveform generator is used, a waveform signal can be directly generated through the built-in AWG of the signal injection module 4.

[0057] An oscilloscope is an electronic instrument that is mainly used to observe and analyze the changes of electrical signals over time and emit noise signals. An oscilloscope can convert voltage signals into visual waveforms and display them on the screen. (The oscilloscope injects the signal into the module 4 through the BNC shielded line to superimpose the noise signal)

[0058] Arbitrary Waveform Generator (AWG) is a highly flexible signal generation device that can generate various complex waveforms customized by users. Unlike traditional function generators, AWG can not only generate standard waveforms such as sine waves, square waves, triangle waves, etc., but also create waveforms of almost any shape according to user needs.

[0059] The control setting compensation module 3 is connected to the noise input module 2. The control setting compensation module 3 is used to control the frequency band of the noise signal output by the noise input module 2 and determine the amplitude compensation amount of the noise signal. The control setting compensation module 3 is also used to determine the amplitude compensation amount of the power supply signal. The control setting compensation module 3 can be a host computer. The control setting compensation module 3 is also connected to the power supply input module 1 through a signal. The control setting compensation module 3 is used to control the output of the power supply input module 1.

[0060] The control setting compensation module 3 determines the amplitude compensation amount of the noise signal at the preset frequency according to the rated power of the test module 5, the preset target amplitude of the noise signal, and the preset frequency of the noise signal. The frequency band of the noise signal ranges from 10Hz to 10MHz. For the specific output compensation process, please refer to the following signal calibration method.

[0061] The signal injection module 4 receives the noise signal and the power supply signal and generates a superimposed noise signal. The signal injection module 4 can be a signal superimposition circuit, after which a driving circuit can be added to enhance the output capability, and then the mixed signal is superimposed on a DC power supply with a larger current through a MOS, and the signal is fed back to the superimposition circuit (generating a mixed power supply with a superimposed noise signal).

[0062] The test module 5 is connected to the signal injection module 4, and is used to receive a mixed power supply with a superimposed noise signal, and output a mixed waveform diagram and test data, which are output by an oscilloscope to a PC for storage. The evaluation board 7 (Evaluation Board, referred to as Eval Board or EVB) is a circuit board used to test, verify and demonstrate electronic components, modules or system functions.

[0063] Based on the same inventive concept, the present invention provides Figure 2 A signal calibration method, based on the noise injection test system provided above, comprises steps S21-S25:

[0064] Step S21, obtaining the rated power of the device to be tested 6.

[0065] The rated power of the device under test 6 refers to the maximum power value at which the device can operate safely and stably under normal working conditions specified by the manufacturer.

[0066] The compensation module 3 may be controlled to obtain the rated power of the device to be tested 6 .

[0067] Step S22, obtaining compensation amplitudes of several noise signals according to the rated power of the device to be tested 6, the preset frequencies of several noise signals and the preset amplitudes of the noise signals, wherein the preset frequencies of the noise signals correspond one to one with the compensation amplitudes of the noise signals.

[0068] Specifically, it includes: obtaining the actual output amplitude of the noise signal at the preset frequency according to the rated power of the device to be tested 6 and the preset frequency of the noise signal; continuously adjusting the compensation amplitude of the noise signal, and when the difference between the actual output amplitude of the noise signal at the preset frequency and the preset amplitude of the noise signal is less than a preset threshold, obtaining the compensation amplitude of the noise signal corresponding to the preset frequency of the noise signal; and constructing a noise signal amplitude compensation table according to the preset frequencies of several noise signals and the compensation amplitudes of several noise signals. The noise signal includes but is not limited to a sine wave.

[0069] The control setting compensation module 3 can obtain compensation amplitudes of several noise signals according to the rated power of the device to be tested 6, the preset frequencies of several noise signals and the preset amplitudes of the noise signals. The present invention provides Table 1 for illustration:

[0070] Table 1

[0071]

[0072] The rated power of the test device 6 is determined, and the preset frequency is 10.00HZ. The control setting compensation module 3 is output according to the preset frequency 10.00HZ of the device to be tested 6, and the preset amplitude is preset. Under the rated power and the preset frequency 10.00HZ, the actual output amplitude of the self-calibration noise input module 2 reaches the preset amplitude;

[0073] Due to the attenuation of the signal, the actual output amplitude obtained by simulation may differ from the preset amplitude of 0.1V. If the difference is less than the preset threshold, no compensation is required. If it is greater than or equal to the preset threshold, compensation is required. The compensation amplitude is determined by continuously iteratively calculating the control setting compensation module 3. When the difference between the actual output amplitude and the preset amplitude is less than the preset threshold, the compensation amplitude of the noise input module 2 at 10.00HZ is obtained. In other words, the control setting compensation module 3 can control the noise input module 2 to output the noise signal at 10.00HZ and a compensation amplitude of 0.351V. Table 1 can be obtained by continuous iterative calculation.

[0074] Step S23, obtaining compensation amplitudes of several power signals according to the rated power of the device to be tested 6, preset frequencies of several power signals and preset amplitudes of the power signals, wherein the preset frequencies of the power signals correspond one to one with the compensation amplitudes of the power signals.

[0075] Specifically, it includes: obtaining the actual output amplitude of the power signal at the preset frequency according to the rated power of the device to be tested 6 and the preset DC component and frequency of the power signal; continuously adjusting the compensation amplitude of the power signal, and when the difference between the actual output amplitude at the preset frequency of the power signal and the preset amplitude of the power signal is less than a preset threshold, obtaining the compensation amplitude of the power signal corresponding to the preset frequency of the power signal; constructing a power signal amplitude compensation table according to the preset frequencies of several power signals and the compensation amplitudes of several power signals. The power signal is a triangular wave.

[0076] The compensation output process of the power signal is similar to that of the noise signal, and the details may refer to the content of the above step S22.

[0077] Step S24, determining a target preset frequency and a preset amplitude of the power signal, and a target preset frequency and a preset amplitude of the noise signal.

[0078] The target preset frequency and the target preset amplitude can be determined according to user needs. For example, a noise signal and a power signal at 10 Hz are both generated, and the noise signal and the power signal at 10 Hz are superimposed and combined to generate a superimposed signal.

[0079] Step S25, obtaining a target superimposed signal and a waveform corresponding to the target superimposed signal according to the target preset frequency and preset amplitude of the power signal and the target preset amplitude and preset amplitude of the noise signal.

[0080] Specifically, it includes: determining the target compensation amplitude of the power supply signal corresponding to the target preset frequency of the power supply signal according to the target preset frequency and preset amplitude of the power supply signal; determining the target compensation amplitude of the noise signal corresponding to the target preset frequency of the noise signal according to the target preset frequency and preset amplitude of the noise signal; and obtaining the target superposition signal and parameters corresponding to the superposition signal according to the target compensation amplitude of the noise signal and the target compensation amplitude of the power supply signal.

[0081] Example: The rated power of the device 6 to be tested is 16W, and the target amplitude of the sine wave output is set to 100mV. The sine wave signal is swept from 10hz to 10MHz by the host computer to obtain the data in Table 1, and the waveform amplitude of 100mV is stably output.

[0082] For example, when the DC component of the power supply signal was 3.13V, 3.3V and 3.47V, a frequency scan from 10Hz to 10MHz and DC component tracking compensation were performed. As the frequency increased, the DAC setting values ​​of the three voltage deviation values ​​of the triangle wave generally showed a consistent change trend. The slight effect of voltage deviation on amplitude compensation can be ruled out here, that is, there is no need to perform calibration compensation separately at the three voltage points.

[0083] Under certain test parameter conditions, the calibration program of this test system automatically matches and calls the lookup table under the test conditions, sets the corresponding compensation parameters to complete the attenuation compensation under high-frequency amplitude, and completes the offset calibration of the voltage pull-off under high-frequency error by fitting the curve function.

[0084] Table 2

[0085]

[0086] When the load power consumption was 22W, a signal superposition test was performed after obtaining the parameter compensation lookup table corresponding to the triangular wave and sine wave frequencies through the host computer.

[0087] The results show that the waveforms before and after superposition show good standard characteristics, and the measured frequency is highly accurate. The amplitude of the superimposed mixed waveform and its expansion amplitude are both within a reasonable range, showing high accuracy. Under the premise of ensuring strong load capacity, the device can effectively perform the task of combining and superimposing signals of various amplitudes and frequency bands. The superimposed waveform shows good integrity and meets the requirements of most test needs. For details, please refer to Figure 3 , Figure 3 a is a sine wave, Figure 3 b is a triangle wave, Figure 3 c is the waveform after superposition.

[0088] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0089] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A noise injection test system, characterized in that: The system includes a power input module, a noise input module, a control setting compensation module, a signal injection module and a test module, wherein the test module includes a device to be tested and an evaluation board; The power input module is connected to the signal injection module, and the power input module is used to input a power signal to the signal injection module; The noise input module is connected to the signal injection module, and the noise input module is used to input a noise signal to the signal injection module; The control setting compensation module is connected to the noise input module, and is used to control the frequency band of the noise signal output by the noise input module and determine the amplitude compensation amount of the noise signal. The control setting compensation module is also used to determine the DC component and amplitude compensation amount of the power supply signal; The signal injection module receives the noise signal and the power signal and generates a mixed power supply with a superimposed noise signal; The test module is connected to the signal injection module, and is used for receiving a mixed power source with a superimposed noise signal, and outputting a mixed waveform diagram and test data.

2. A noise injection test system as claimed in claim 1, characterized in that: The control setting compensation module is used to determine the amplitude compensation amount of the noise signal, including: The control setting compensation module determines the amplitude compensation amount of the noise signal at the preset frequency according to the rated power of the test module, the preset target amplitude of the noise signal, and the preset frequency of the noise signal.

3. A noise injection test system as claimed in claim 1, characterized in that: include: The power input module includes a power adapter or a programmable power supply.

4. A noise injection test system as claimed in claim 1, characterized in that: include: The noise input module includes an arbitrary waveform generator or an oscilloscope.

5. A noise injection test system as claimed in claim 2, characterized in that: include: The frequency band of the noise signal ranges from 10Hz to 10MHz.

6. A signal calibration method, characterized in that: A noise injection test system according to claims 1-5, the method comprising: Get the rated power of the device under test; According to the rated power of the device to be tested, the preset frequencies of the noise signals and the preset amplitudes of the noise signals, the compensation amplitudes of the noise signals are obtained, wherein the preset frequencies of the noise signals correspond to the compensation amplitudes of the noise signals one by one; According to the rated power of the device to be tested, the preset frequencies of the plurality of power signals and the preset amplitudes of the power signals, the compensation amplitudes of the plurality of power signals are obtained, wherein the preset frequencies of the power signals correspond to the compensation amplitudes of the power signals one by one; Determining a target preset frequency and a preset amplitude of a power signal, and a target preset frequency and a preset amplitude of a noise signal; According to the target preset frequency and preset amplitude of the power signal and the target preset amplitude and preset amplitude of the noise signal, a target superimposed signal and a waveform diagram corresponding to the target superimposed signal are obtained.

7. A signal calibration method as claimed in claim 6, characterized in that: According to the target preset frequency and preset amplitude of the power signal and the target preset amplitude and preset amplitude of the noise signal, a target superposition signal is obtained, including: Determining a target compensation amplitude of the power signal corresponding to the target preset frequency of the power signal according to the target preset frequency and the preset amplitude of the power signal; Determining a target compensation amplitude of the noise signal corresponding to the target preset frequency of the noise signal according to the target preset frequency and the preset amplitude of the noise signal; A target superposition signal is obtained according to a target compensation amplitude of the noise signal and a target compensation amplitude of the power supply signal.

8. A signal calibration method as claimed in claim 6, characterized in that: According to the rated power of the device to be tested, the preset frequencies of the noise signals and the preset amplitudes of the noise signals, the compensation amplitudes of the noise signals are obtained, including: According to the rated power of the device to be tested and the preset frequency of the noise signal, an actual output amplitude of the noise signal at the preset frequency is obtained; Continuously adjusting the compensation amplitude of the noise signal, when the difference between the actual output amplitude of the noise signal at the preset frequency and the preset amplitude of the noise signal is less than a preset threshold, obtaining the compensation amplitude of the noise signal corresponding to the preset frequency of the noise signal; A noise signal amplitude compensation table is constructed according to the preset frequencies of the plurality of noise signals and the compensation amplitudes of the plurality of noise signals.

9. A signal calibration method as claimed in claim 6, characterized in that: According to the rated power of the device to be tested, the preset frequencies of the plurality of power signals, and the preset amplitudes of the power signals, the compensation amplitudes of the plurality of power signals are obtained, including: According to the rated power of the device to be tested and the preset frequency of the power signal, an actual output amplitude of the power signal at the preset frequency is obtained; Continuously adjusting the compensation amplitude of the power signal, when the difference between the actual output amplitude at the preset frequency of the power signal and the preset amplitude of the power signal is less than a preset threshold, obtaining the compensation amplitude of the power signal corresponding to the preset frequency of the power signal; A power signal amplitude compensation table is constructed according to the preset frequencies of the plurality of power signals and the compensation amplitudes of the plurality of power signals.

10. A signal calibration method as claimed in claim 6, characterized in that: include: The power signal is a triangle wave and is used to test the voltage tolerance; The noise signal is a sine wave and is used to test the noise margin.

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