Home Literature Review Requirement sheet Hardware Design
1. Functional Features
These are the features which are designed and implemented in this project. They form the basic requirements that are taken into account during the design process.
· Two input channel: The scope should be able to sample and display two input signals simultaneously with each channel independently configured to measure any one among three physical quantities.
· Internal and external triggering modes: The scope should support edge triggering, level triggering and pulse triggering in both the internal and external mode. In Internal triggering mode, the characteristics of the sampled input signal is used for triggering. In external triggering mode the characteristics of the external signal is used to trigger the input signal.
· X-Y plot: The scope should be able to plot the points corresponding to instantaneous values in channel 1 and channel 2 in X-Y graph.
· Wide time base: The time base of the scope should be able to be varied from 100ns to 10s when it’s operating in normal oscilloscope mode. Both the channels should have identical time base.
· Automatic measurement of waveform parameters: The scope should be able to automatically measure various parameters associated with the input waveform such as Frequency, Time period, Mean, R.M.S, Rise Time, Fall Time, Peak to Peak, etc.
· 3.3Vp-p Calibration signal: The scope should output a reference signal which can be used for calibration. The reference signal must be a 3.3 Vp-p square waveform.
· Pure AC or Pure DC component measurement: Both the channels should support AC and DC coupling.
· Maximum record length of 1024 points: The scope should be able to capture up to 1024 samples in one run.
· Maximum Analog bandwidth: The scope should be able to measure analog signals of frequency up to 20MHz.
· Cheaper design: The scope should have minimum cost which do not exceed 10,000 INR.
· 4.3 Inch LCD Display with touchscreen interface: The scope should have a 4.3 Inch (diagonal length) LCD of resolution 480*272 pixels.
· Zoom and pan: Zoom is a facility to change the volt per division as required and pan is the facility to move or shift the waveform as required. The scope should provide both of these facilities.
· Cursor Function: Cursor function is a facility where the user can make use of cross axes to read off the value corresponding to the intersection of two axis. The scope should support this feature.
· Spectrum Analysis: The scope should have facility using which the user can observe the input waveform in frequency domain.
· Math Functions: The scope should provide basic mathematical operations such as addition, multiplication and subtraction.
· Software Compensation: This is one of the methods which can be used to reduce the undesirable response characteristics of the data acquisition system.
2. Requirement Sheet
The Requirements sheet is a detailed list of technical specifications. All the mandatory features are further expanded to determine exactly what has to be done under these individual features.
· Two input channel: The scope should have two channels which could be configured to measure any one among the three physical quantities as shown below.
Internal and external triggering modes: The following list specifies the exact condition which has to be evaluated for triggering. For internal triggering, the condition is evaluated on the input signal while for the external triggering the condition is evaluated on an external signal fed to the ‘external trigger’ (physical channel).
1. Positive Edge triggering – A positive edge that crosses the trigger level set by the user.
2. Negative Edge triggering – A negative edge that crosses the trigger level set by the user.
3. Positive level triggering – A positive level that is greater than the trigger level set by the user.
4. Negative level triggering – A negative level that is lower than the trigger level set by the user.
5. Pulse triggering – A signal with ‘n’ pulses of width greater/smaller as specified by the user (Optional feature).
· X-Y plot: The scope should be able to plot the relationship between various signals measured at input channels. This is achieved by plotting points in an x-y coordinate plane with each points having its x-coordinate equal to the sample value of channel 1 and its y-coordinate equal to the sample value of channel 2. Some of the details are given below:
1. As the samples are collected the points corresponding to those samples are updated on screen.
2. The axes can have variable scale which can be set using control panel.
3. Interpolation between two consecutive points is user configurable (optional feature).
· Wide time base: The variation of time base should follow the sequence specified below:
The part of the screen used to display waveform should be divided in such a way that 8 or 10 divisions are made along horizontal direction. Time base is indicated for such divisions.
· Automatic measurement of waveform parameters: The scope should be able to measure some of the waveform parameters such as Amplitude, Minimum and Maximum value, Peak to Peak value, Frequency, Time Period, etc.
· 3.3Vp-p Calibration signal: The scope should output a reference signal which can be used for calibration. The reference signal must be a 3.3 Vp-p square waveform of variable frequency.
· Pure AC or Pure DC component measurement: Both the channels should support AC and DC coupling.
1. In AC coupling the DC off-shift is reduced to zero and only the time-varying component is shown on screen.
2. In DC coupling the DC offset is not reduced to zero. The waveform is shown in its original form.
· Maximum record length of 1024 points: This is the maximum number of sampled values which is used for construction of one waveform. Only a part of the waveform is shown on the screen. When the scope is paused the user can pan across the waveform to view its entire length.
· Maximum Analog bandwidth: The scope should be able to measure analog signals of frequency up to 20MHz. The scope should have flat-band band characteristics to a frequency of up to 20MHz. All higher frequencies must be attenuated to prevent errors due to aliasing.
· Cheaper design: The scope should have minimum cost which does not exceed 10,000 INR.
· 4.3 Inch LCD Display with touchscreen interface: The scope should have a 4.3 Inch (diagonal) LCD of resolution 480*272.
· Zoom and pan: The list shows the various configurations for zoom function (variable volt/div)
Panning is used to navigate across the waveform. When a waveform is shown on screen panning controls can be used to move or shift the waveform to the top or bottom of the screen.
· Cursor function: The cursor function when activated must display a cross axis with the corresponding time for vertical axis and voltage for horizontal axis. The user should be able to position the axis anywhere on the screen.
Moving the axes off the screen should pan the waveform, provided that it does not exceed a specified limit.
· Spectrum analysis: The scope should have facility where the user can observe the input waveform in frequency domain. This is achieved by computing the Fourier transform of the sampled signal. The frequency range 0 to fs/2 (half of sampling frequency) is divided into 200 points and the amplitude and phase of corresponding frequency component is calculated. The frequency range over which this is done should be variable within the limits.
· Math Functions: The scope should provide basic mathematical operations such as addition, multiplication and subtraction. The result of adding, multiplying or subtracting two signals results in a third signal which will be displayed on screen. This waveform is referred to as math waveform.
· Software compensation: The scope should be able to offset the undesirable characteristics of signal path such as attenuation, DC level shifting, etc.
The compensation is done in two stages. In the first stage the DC level is adjusted so that when signal input is grounded the scope shows 0 level. In the second stage the sampled signal is processed by DSP filtering which reduces the uneven phase and magnitude response of the data acquisition system. The user should be able to enable or disable software compensation as required.