Week5

1.       Progress Made:

This week I mainly did two tasks. The first one is that I ordered a bench in the 4^th floor laboratory room. The number of bench is 11b. Then on Saturday, I searched some information about ERG test on the internet. ERG is an abbreviation of electroretinography. ERG is to measure the electrical responses of many retina cells. During the ERG test, patients are asked to be in a sitting or lying position. In order to avoid some discomfort, the doctors will place numbing drops in advance. Next, the eyes of patients are kept open by a device named tractor. Then, an electrical sensor or electrode is put near each eye. The electrode will measure the electrical activity of the retina responding to light. A light flashes, and the corresponding electrical response will be sent to a TV-like screen for instance CRT, LCD monitors where the response is able to be viewed and recorded from the electrode. The normal response pattern has waves a and b. Meanwhile, the resulting signal displays the function of time vs the signal’s amplitude which most reflects in voltage.  This kind of signals is quite tiny and recorded in microvolts or nanovolts. The doctor will take the readings in normal room light and in the dark respectively.

Furthermore, I also read some literatures about the historical view of ERG. It chiefly tells how the response of the eye to a light flash is discovered. At the meantime, it also refers to the detailed introduction to four kinds of waves of electrical response, like wave-a, wave-b, wave-c and wave-d. However, in my opinion, there is no need for me to do further reading about this knowledge. Hence, I attempted to search some articles about both ERG test and CRT or LCD. I wanted to know how to connect the electrodes to the CRT or LCD monitors. CRT or LCD monitors are commonly regarded as stimulus sources for ERG test. There are some screen properties which ought to be achieved for stimulus source CRT monitor, for instance, frame frequency, luminance and calibration. I haven’t finished reading the corresponding literatures about this knowledge. I will continue to read them next week.

2.       Problems and Challenges:

This week I spent less time on doing FYP. Therefore, by now I am unable to grasp a clear understanding of ERG test. I don’t know the significance of high quality image display of responding waveforms to ERG test. I also have no idea about how to connect the ERG knowledge and DMD knowledge together to implement the objective of my FYP. I want to know whether we need electrodes in my FYP or just establish a proper monitor.

3.       Plans for Next Week:

Next week, I will spend a lot of time on my FYP. This week I really did few tasks and merely spent less than one day. Next week, I will spend two to three days to do my FYP. To begin with, I will continue to read literatures about both ERG test and CRT or LCD monitors. I should understand them fully not partially. Then on the basis of those knowledge, I will think about how to conduct my FYP. If my equipment arrives, I will investigate how to use it. Now I still face a lot of confuses and even misunderstandings about my FYP, and I should make any effort to have a clear and correct cognition of my FYP as soon as possible.

4.       Reference：

1, Electroretinography, U.S. National Library of Medicine, 11 April 2005 (accessed 19 January 2007),http://www.nlm.nih.gov/medlineplus/ency/article/003388.htm

Week 4

1.       Progress Made:

This week I have tried to find more literatures about my project. Firstly, I searched for some materials about DMD in the IEEE website. Meanwhile, I wanted to find some resources about the application of DMD. Luckily, I found 4 articles about DMD. After reading the DMD background theories in them, I have a deep understanding of the work principle of DMD. However, the applications in them like volumetric 3D display do not have a close relationship with my FYP. In fact, I wanted to learn how the authors investigate their project, but they refer to too much technical knowledge. In my opinion, they may not give big favour to my project. Hence, eventually, I took notes about DMD work principle in my log book. This work principle is quite in detail.

DMD Principle:

l  The DMD pixel, which is an integrated micro-electronic mechanical system (MEMS) structure, is manufactured on a CMOS static random array memory (SRAM) cell.

l  The mirror (aluminia) is linked to an underlying yoke.

l  The yoke is connected by two thin, mechanically compliant torsion hinges (also aluminia).

l  The hinges are held by the posts which stick on the underlying substrate.

 (Explanation for some items:

Hinge: A kind of bearing linking two objects which allows a restricted angle of rotation between them.

Yoke: A beam applied between a pair of objects to capacitate them to pull together on a load. )

l  There is an electrostatic field between memory cell, yoke and mirror, which produces an electrostatic torque. This kind of torque works opposed to the restoring torque of the hinges to make the mirror rotate in the positive or negative direction.

l  The mirror and yoke rotate until the yoke comes to rest against mechanical stops which have the same potential as the yoke.

l  The address electrodes under the yokes are linked to SRAM cell.

l  The yoke and mirror are linked to a bias bus which interconnects the yoke and mirrors of each pixel to a bond pad at the chip perimeter

l  The yoke is attracted to one or another address electrode relying on which one is activated.

l  Which of the electrodes is activated relies on the state of the SRAM cell.

l  A 1 stored in the cell will lead the mirror to rotate to the degree between +10 and +12 degrees to an on state.

l  A 0 is stored in the cell will cause the mirror to move to the degrees from -12 to -10 degrees to an off state.

l  If the memory cell is nether 1 or 0, there is no electrostatic force on the mirror. The torsion hinges will cause the mirror to 0 degree.

l  If the mirror is tilted in either direction, a bias current will keep it in the current position even if a new bit of data is being loaded into the SRAM cell.

Electronic working principle:

1)        Memory ready-All SRAM cells have been loaded with the new address states.

2)        Rest-All mirrors are reset in parallel position (voltage pulse are applied to the bias bus).

3)        Unlatch-The bias is removed to unlatch mirrors and permit them to release and begin to rotate to flat state

4)        Differentiate-Under the retarding fields, the mirrors which keep in the same state from those that are to cross over to a new state are separated.

5)        Land and latch-The bias is restored in order to capture the separated mirrors and help them to rotate to the address states, then settle and latch.

6)        Update memory array-The bias keep turning on to make the mirrors latched in order to stop them from responding to changes in the memory, while the SRAM cell is written with new video data.

7)        Repeat sequence starting at step 1.

Furthermore, I searched the merits of DMD technology which mainly reflect in four aspects.

  Digital advantage

Since DMD applies the digital signal, it is able to save the time and cost for the analogue digital conversion and have lower noise. Nevertheless, other display techniques still use analogue signal, like LCD.

  Reflective advantage

DMD is a reflective device which can achieve the light efficiency larger than 60%. However, LCDs are polarization-dependent devices so that it cannot get the 50% of the lamp light.

  Seamless picture advantage

DMD has a quite high fill factor up to 90%. The reason is that DMD mirrors are 16um square and the interval between them is just only 1um. Therefore, DMD can achieve higher perceived resolution due to high fill factor, finally which produces natural and lifelike image. By contrast, LCDs can just reach 70% fill factor.

  Scale advantage

DMD systems are high integration so that the DMD projectors can be produced much lighter and smaller.

Then I read three articles about the application of DLP LightCrafter. As a matter of fact, I wanted to know how those researchers develop a prototype by DLP LightCrafter.  Nevertheless, DLP LightCrafter is not their main equipment. Those articles do not introduce how they use this equipment to implement their objectives.

2.       Problems and Challenges:

At present, I merely know the operation principle of DMD. There are following problems needed to figure out. To begin with, I do not know what kind of field in clinical eye testing will be applied by the DLP LightCrafter. Furthermore, it is difficult to find other resources about the using methods for DLP LightCrafter. Maybe I can understand the equipment better when I get it.   

3.       Plans for Next Week:

In the next week, maybe I can get DLP LightCrafter. I can do the project in the 4^th floor of EEE building. On Tuesday, I will learn to use the equipment in the lab room. I will do my best to be familiar with all the connectors in the DLP LightCrafter.

Reference:

L J. Hombeck, Current Status of the Digital Micromirror Device (DMD) for Projection Television Applications, http://ieeexplore.ieee.org.ezproxy.liv.ac.uk/stamp/stamp.jsp?tp=&arnumber=347329

Week 2-3

  Progress Made:

In week 2 and 3, I mainly completed two tasks which are FYP presentation and FYP specification form respectively. I just did some further research about some general ideas about my FYP, for instance, the principle of DMD.

Figure 1 shows a schematic of 2 DMD mirror pixels.

Every mirror is put on a yoke that is linked to 2 support posts by compliant torsion hinges. For this kind of hinge, the axle is fixed at two ends and twists in the middle. Then according to electrostatic attraction, the positions of the mirrors are controlled by two pairs of electrodes. Most of time, equal bias charges are applied to these two electrodes at the same time. Hence, the mirror will keep its position. However, if you want to move this mirror, you can load the required state to the SRAM (static random array memory) cell which is under the mirrors. When all the SRAM have been loaded, the bias voltage will be removed and the mirror can rotate. Nevertheless, if you still want to stable the mirror, you can restore the bias voltage.

Figure 2 displays how DMD display system work. There are two micromirrors in this figure. Each micromirror is able to rotate +12  or -12  to an on or off state. This on or off state is determined by the binary state of SRAM cell which is under each mirror. In on state, the light from the lamp can be reflected into the projection lens, making the pixels bright on the screen. However, in off state, the light is directed elsewhere making the pixels dark.

I did not do some reading about the details about DLP LightCrafter components, which is in my plan in the last week. The reason is that I misunderstand my jobs in the FYP. What I should focus on in my FYP is to learn how to use this equipment rather than study the configuration of it.

  Problems and Challenges:

By now, I do not have a clear understanding of my FYP. I do not know the deep knowledge of both DMD technology and DLP LightCrafter. What is worse is that I do not have a distinct idea about my final prototype of DMD display systems for clinical eye testing. Hence, these are several serious problems and challenges I meet at present. I have to figure out these as soon as possible.

  Plans for Next Week:

l  Establish a blog and record my progress

l  Search some materials on IEEE about DLP technology, DMD technology and DLP LightCrafter

l  Read the principle, advantages and application of  DLP and DMD technology

l  Read alternative projection techniques, like LCD

Reference:

1, Dana Dudley, Walter Duncan, John Slaughter, Emerging Digital Micromirror Device (DMD) Applications, http://www.loreti.it/Download/PDF/DMD/paper_dmd.pdf

Week 1

Progress Made:

This week I mainly read the user’s guide of DLP Light Crafter named DLP Light Crafter^TM Evaluation Module (EVW) user’s guide. According to this material, I grasp a basic understanding of our tools, like their hardware and software overview. Meanwhile, the objective of Light Crafter is to permit developers to assess TI’s (Texas Instrument’s) DLP Pico platform along with TI’s DaVinci Technology and the DM365 architecture (S1). To begin with, with respect to DLP Pico platform, it is intended to develop DLP Pico Projector. The features of DLP Pico Projector are shown below:

l  Ultra portable and compact

l  Easily connected to nearly any device’s video out port

l  Long lasting solid state LED illumination

l  Astounding picture quality

l  DLP Pico chipset

In the comparison to the third feature, others are readily to be understood. For solid state lighting (SSL), it is a type of lighting which utilises semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs) or polymer light emitting diodes (PLEDs) as sources of illumination rather than electrical filaments, plasma or gas. It has several prominent advantages such as lower energy consumption, longer life time and high efficiency. Furthermore, TI’s DaVinci is a kind of system on a chip family which combines a DSP (Digital Signal Processing) core based on the TMS320 C6000 VLIW  DSP family with an ARM architecture CPU core (S2). Moreover, DaVinci Technology is a signal processing-based solution tailored for digital video applications which supplies video equipment manufacturers with integrated processor, software, tools and support to simplify the design process and accelerate innovation (S2).

Hardware Overview

In addition, the Light Crafter chiefly comprises of three subsystems which are light engine, driver board and system board respectively. Firstly, light engine consists of the optics, red, green and blue LEDs, and the 608 604 diamond pixel 0.3’’ WVGA (Wide Video Graphic Array) DMD (Digital Micromirror Device) (S1). DLP 0.3 WVGA chipset includes two components DLP 3000 that is 0.3 WVGA DMD and DLPC300 which is DLP3000 digital controller (S3). The key features of DLP3000 are displayed below:

l  608 684 micromirror diagonal (608 columns and 684 rows)

l  0.3-inch array diagonal

l  Up to WVGA (854 480) image display

l  7.6um micromirror pitch (Every aluminium micromirror is approximately 7.6um in size. This micromirror is able to be switchable between -12  and 12 )

l  Side illumination for compact optics

The function of DLP3000 is highly efficient, digitally controlled MEMS (Micro-Electromechanical Systems) micromirror array can display binary patterns up to 4000Hz (S3). Additionally, it can be applied to modulate the amplitude and direction of incident light. It also has some benefits, for instance fast and reliable spatial light modulation in a form of factor for lower cost, portable, embedded, and hand-held equipment (S3). Moreover, the key features of DLPC300 are:

l  Pattern rates up to 4000Hz binary, 120 Hz grayscale

l  Output trigger for camera or peripheral synchronization

l  Low power consumption (93mW typical)

The purpose of DLPC300 is to provide a convenient interface for user electronics which assures reliable operation of the DMD. Meanwhile, due to it, developers can control the mircromirrors light sources, and peripherals for high speed and intelligent pattern or video display (S3).

Furthermore, driver board comprises of LED driver circuits, DLPC300 DMD Controller, power management, circuits and MSP430 (S1). System board includes TMS320DM365, FPGA (Field Programmable Gate Array) and several connectors for external inputs (S1).

Software Overview

The software is on the basis of TI’s DVSDK (Digital Video Software Development Kit) platform (S1). DVSDK is a collection of royalty free software components established on Linux operating system and pre-tested by TI. This section in the user’s guide material is to introduce the simple knowledge about the components of the software and the embedded Linux Kernel. Moreover, it tells users how to install the software on PC. 

Problems and Challenges:

In this week, I merely grasp a basic understanding of Light Crafter. There are numerous areas I ought to study further. For instance, I want to do more research about DLP 0.3 WVGA chipset like its block diagram and how DLPC300 and DLP3000 work together. Furthermore, I should investigate the work principles of DLPC300 and DLP3000. I have difficulties in understanding the figures about micromirror array in the source DLP 0.3 WVGA Series 220 DMD. I should find more materials about these for the sake of grasp them. There are some terminologies I do not understand their significances to the image display, such as grayscale and angular positions, frame rate, bit-plane etc. I should be familiar with using the software about Light Crafter. I should learn how to control the micromirror to obtain the image display we desire. I ought to know the image display requirements for eye testing.

Plans for Next Week:

Next week, on the basis of the knowledge I study this week, I will do further research about them, especially for the micromirror figures. I will investigate their contributions to the final image display. Furthermore, I will do some reading about eye testing. 

Reference:

1, Texas Instruments, DLP LightCrafter Evaluation Module (EVM) User’s Guide, 2013, http://www.ti.com.cn/cn/lit/ug/dlpu006b/dlpu006b.pdf

2, Texas Instrument, DaVinci technology

3, Texas Instruments, DLP 0.3 WVGA Series 220 DMD, http://www.ti.com/lit/ds/dlps022a/dlps022a.pdf