What is the purpose of eye diagrams?
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Eye diagrams are used to measure the quality of a signal of an electronic device. More specifically, they identify the “eye opening” or how many samples are considered to have come from a perfect non-noise input signal at any given point in time.
A person’s eye is like an X-Rays that creates a picture of the world in two dimensions. A camera processes what we see in 3 dimensions by sampling 2D information and combining it for each pixel into one number (3 numbers per pixel). Electronic devices convert analog voltages into digital bits which becomes zeros and ones inside a computer or transistor – this involves sampling every fraction of a second where the voltage goes above some threshold as true 1’s, below 0 volts as false 1’s, and all other places as a value representing that voltage. This is called the sampling theorem which says that this process must be done very quickly and is the basis of the eye diagram.
Each picture element on a display is created by lighting up individual pixels in sequence while an electron beam scans across them (scanning or raster).
The beam moves from left to right and top to bottom creating the lines. While the beam is not moving it is turned off, so each line is created by turning the beam back on and then back off again as soon as possible:
When we create a digital signal that’s similar but not identical to the original analog signal, we get noise added in from outside which can be from any other device or a combination of several. When this happens it creates a fuzzy “red” area around the edges:
The eye diagram is a map created by plotting how many samples fall within the “eye”. The bigger and more uniform this area becomes the better the signal is.
Eye diagrams are used in digital signal analysis and can be used to study the timing of a digital system.
An eye diagram is a probability density function (PDF) which shows the probabilities of any given bit or sequence, per unit time occurring on an interface. Typical uses for an eye diagram include calculating the baud rate of connections between data terminal equipment and serial communication networks by observing when reflections appear to line up; checking for common-mode voltage spikes; identifying stuck bits and other errors caused by noise or interference, or measuring transmission quality at lower speeds.
The line in a skew plot, or eye diagram, is the power of the signal divided by the noise. This can be correlated to bandwidth which defines how small of interference a receiver can tolerably suffer and still recover a large amount of bits from a pseudo-random binary sequence signal. In telecommunications, many channel models are based on this idea.
Eye diagrams allow you to identify if your coaxial cable has been damaged or disturbed by looking at plots that compare signal quality before and after it has passed through damage (i.e. visually showing you where there’s no longer an even line.) The absence of an even “eye” underneath detected disturbs points out where the transmission capability is likely to be affected.
This is because an eye diagram shows the quality of the signal by how wide the lines are. The higher the quality, generally speaking, the better defined and closer together the eye will be.
The eye diagram contains a record of the waveform or impulse response plot of what happens when light enters an optical device, such as a camera lens. The properties of the curve are used to diagnose image defects and optimize imaging systems.
Eye diagrams have become very important in smartphones, tablets, and other devices where displays are getting more compact because they offer better ways to detect missed pixels or films that don’t cooperate well with touch screens. Eye diagrams can be found inside cameras that play a role in determining sharpness (sometimes by creating visual contrast) when different parts of an image create blur due to aberration errors from the lens system; here they illustrate three specific things about how pixel blurs meet at picture edges: Diffraction causes the blur circle to widen, partly out of focus objects add white noise around the main blob.
Eye diagrams are graphics that can be used to describe the loss of transmitted light, received light, and reflected/diffracted light.
The eye diagram shows how much of the signal is lost or discarded by the optical system as a function of time. For example if you are looking at a sinusoidal wave with a maximum TRV-transit time = 0.1 ms then 1% will be lost in the first 10 µs and 90% will be lost after 100 μs (i.e., it is very fast). And this applies to all lighting conditions from dimmer lights where more energy is needed for human eyes to see 3D images (30 lux) up to outdoor bright sunlight where only 8% is lost (it is very slow).
The eye diagram also shows the actual voltage at any time (up) and the maximum expected voltage that was sent by the encoder (Vmax), both of these are important for triggering or strobe control circuits. This information can be used to design specialized lighting conditions which gives better 3D perception e.g., High Dynamic Range (HDR) and Active Stereo.
The actual voltage at any time (V(t)) is the ideal voltage that was sent by the encoder minus the loss due to optical receiver or receiver circuit; V(t)=Vmax-Loss. So if Loss=0.5% for a certain time period, the voltage at this time period will be 0.5% less than the normal strobe voltage sent by the encoder. Furthermore it is a good idea to check for fast transients and overloads, so one can see if V(t) is close to or higher than Vmax.
In summary, eye diagrams provide insight into how the optical system is performing in a given lighting condition.
Measurement of the quality of a radio-frequency signal (phase and magnitude)
In electronics, an eye diagram or web chart can be used to show the response time and amplitude comparison between two signals. The electrodes placed on your head also work in this way – measuring electrical activity from our brains that varies with moods, emotions, thoughts etc. Eye diagrams are also used extensively to measure radiation dosages leaked from electronic devices which emit electromagnetic radiation such as laptops and cell phones. And finally – eye diagrams are used in scientific equipment such as lasers, projectors, missile guidance systems etc… since they tell us how effectively photons or radio waves are being emitted from these instruments to various receivers (eg detectors). Essentially we use eye diagrams when measuring the quality of a signal.
Eye diagrams are created using Fourier transforms . They show us how our eyes / brain interpret an electromagnetic wave by superimposing two waveforms, one which goes into our retina and another one after it’s been processed in our brains.
Eye diagrams can help characterize DUT timing parameters such as visual rise time and fall time, eye aperture jitter or spread, the duty cycle of a device, and overshoot (time spent going faster than the maximum tolerated speed).
The line in a skew plot, or eye diagram, is the power of the signal divided by the noise. This can be correlated to bandwidth which defines how small of interference a receiver can tolerably suffer and still recover a large amount of bits from a pseudo-random binary sequence signal. In telecommunications, many channel models are based on this idea.
Eye diagrams describe how bright or dark an area of a photograph is and, by implication, whether that area is particularly detailed.
The eye diagram on the left has a wide curve with distinct peaks indicating high detail in low-light areas while that on the right is narrow and less detailed suggesting limited detail in darker areas. The most important thing to note about this option — aside from what it does well (low-light detail) — is what it doesn’t do so well: It struggles mightily at figuring out details in lighter regions of the photo.
To define the type and strength of spectral energy present in a beam of light.
An eye diagram is used to graphically display the amount, shape and distribution of energy in a solid-state laser beam. The original purpose was to identify properties that may affect lasing performance such as mode quality, transverse modes position on both vertical wall or horizontal plane. They are typically produced by calibration using lenslet or holographic sources for determining relative intensity. In particular these include mode quality (defined as full‐width at half maximum) and effective divergence (about 5% less than nominal) with well aligned vertical and horizontal scatters for single transverse modes operation at centre wavelength.