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Bench 5

Page history last edited by pbeck@... 16 years ago

PB - 3/17/08 - Modified wiki based on comments

VB - 3/8/08 - Added some comments to bench 3 and 7 wikis

 


Integrated circuits make modern technology possible and therefore have significant effects on Equity, Environment, Economy, and Energy. Dependence on energy intensive materials forms a significant shortcoming in integrated circuits and modern electronics.

 

The shift register has many uses in digital electronics. It can perform multiply and divide operations by simply shifting a bit left or right. Without this vital circuitry, digital computing would not be the same. In experiment 5, we investigate its operation and the frequency at which it can operate. We find it has a large operational frequency range, making it useful in systems that run at many different clock cycles. The operating frequencies for this specific shift register ranged from .01Hz to 6.3MHz. Modern shift registers offer much higher frequency performance. A large operating range offers two advantages. High frequency operation allows for high speed calculations, and low frequency operation uses little power since CMOS power dissipation and operating frequency are proportional. A design that incorporates both modes demonstrates energy efficiency, which means low operating costs (an equity concern).

 

 

CMOS, Transmission Gates, and TTL NAND Inverters cost very little. Modern IC fabrication techniques allow for single chips to contain a great many transistors. The two stage shift register built in this lab only uses 16 transistors, not including the circuitry that generates the clock and anti-clock signals. Shift registers that can handle many bits, not just one, can be built on one chip. Putting the required circuitry on one chip, rather than four, reduces material use and costs.

 

In one experiment, we measure average power dissipation for a CMOS NAND array (74HC00) and two TTL NAND arrays (7400 and 74LS10) with a 5V high rail. At 1MHz operating frequency, the 74HC00 consumed only 0.55mW per gate, the 7400 consumed 11.4mW per gate, and the 74LS10 consumed 2.82mW per gate. Reporting these figures at a 1MHz operating frequency better describes how these families dissipate power at even higher frequencies, like in modern technologies. Obviously, the 74HC00 consumes the least power. However, as operating frequency increases, the 74HC00 power requirement increases linearly, possibly leading to higher dissipation than TTL at very high frequencies. Power dissipation in Both TTL families stays very constant with frequency changes. The "LS" designation in the 74LS10 package stands for Low Power Schottky TTL and it indeed consumes much less power than the standard TTL. 

 

ECL, or Emitter Coupled Logic, forms an important high speed requirement in digital logic. Our test circuit uses 0 and -5.2 volts as its power supply rails and a reference voltage Vr = -1.15 volts. It uses four transistors from the CA3086 chip that contains 5 NPN bipolar junction transistors. Transistor Q5 remains unused in this circuit. Two BJT's, with emitters connected, form the basic ECL circuit. The second two BJT's act as voltage followers to produce logic NOR and OR functions on their emitters. At a high input voltage Vin = -0.75 volts, this gate consumes 43.7 mW.  At a low input voltage Vin = -1.55 volts, it consumes 42.1 mW. On average, this ECL gate consumes 42.9 mW. This gate dissipates considerably more power than the CMOS and TTL gates.

 

Lower power dissipation has become a very important requirement in digital electronics. When a device consumes too much power, it yields higher heat output which in turn damages components. Damaged components create more waste. Also, with components that dissipate more heat, we must employ more elaborate cooling systems to ensure correct operation and avoid damage. These extra cooling systems only help to drive up cost in products utilizing digital circuity. This fact makes it more difficult for low income groups to purchase these devices. Designers and manufactures must strive to use low power options, like Low Power Shottkey TTL, to reduce power dissipation. The lower the power demand in a product, the more affordable it becomes.

 

 

Building a single desktop computer requires over 20kg of toxic chemicals for the semiconductor fabrication and circuit board fabrication (a significant detriment to the environment, production economy, and equity since disposal often occurs in low-income areas). Correlations appear to exist between exposure to these chemicals and higher birth defect, miscarriage, and cancer rates (another equity issue affecting residents near disposal areas and fabrication workers). However, "connections between long-term exposure and illness are notoriously difficult to prove (or disprove)"[3].Personal computer production also requires many energy intensive materials, such as epoxy, aluminum, and steel, which account for a 6 MJ production cost in a single desktop unit. With all components (IC's, PCB, monitor, bulk material and chemical production) considered, the production energy uses add to over 5 GJ per unit (enough energy to power over 25 average households for a year).[3] Energy use clearly connects all 4 E's of sustainability.

 

Fossil fuels form the most prominent energy source[4] (this relates to electronics fabrication through material transportation, acquisition, and energy production). Using fossil fuels produces 21.3 gigatons of carbon dioxide per year, contributing to the greenhouse effect and global warming (an obvious environmental and equity concern). Among other fossil fuels, oil forms a large fraction of total use.[5] Global oil use depends strongly on the middle east and north Africa.[6] [9] Oil production dominance in some areas leads to trouble maintaining livelihood when oil supplies decline. Villages that originally sustained themselves through farming or logging sometimes work for so long in oil businesses that they forget how to support themselves as they once did.[7] A much larger scale problem arises in the waste and destruction associated with acquiring oil.

"The allegation that the Iraq was mainly about oil has since been supported by the remarks of Alan Greenspan, the recently retired head of the US Federal Reserve. In media coverage in advance of the publication of his memoirs, Greenspan is reported to have written that,

"I am saddened that it is politically inconvenient to acknowledge what everyone knows: the Iraq war is largely about oil." [8] The direct environmental damage due to battle, indirect damage associated with mass producing war materials, large energy investment in destructive rather than constructive materials, and effects on human life and livelihood (equity) all clearly  go against the sustainability principles. Oil use also presents a clear environmental risk, since greater than 10,000 tonnes spill from tankers every year. [10]

 

We must always consider a product's source. Although oil only serves in computer production, some elements that go directly into IC circuitry have significant effects abroad. All electronics containing IC's require capacitors which pose a significant sustainability issue, since Tantalum often serves as the metal electrode (and Tantalum Oxide as the dielectric). Mining Tantalum, most commonly found in the Congo, helps fuel bloody civil wars over the prospective wealth source [2]. e-Waste also presents an obvious equity and environmental issue abroad, since roughly 20 million pounds left California ports alone in 2006. [11] 

 

Toxic materials in electronics pose risks both during manufacturing and disposal. Beryllium (Be) appears in PCBs and other application due to its conductive properties, light weight, and high strength. However, inhaling Be dust often leads to incurable Chronic Beryllium Disease which has many serious symptoms. [12] [13] Gallium Arsenide in semiconductor circuitry becomes a disposal problem. Acidic environments can cause the compound to break down and arsenic may seep into groundwater. [14] These two problems pose a risk to the environment and to people involved in production and those living near disposal sites,

 

 

 

[1] Wikipedia, The Free Encyclopedia ‚Dynamic random access memory. Available http://en.wikipedia.org/wiki/Dynamic_random_access_memory [Accessed February 15, 2008]

[2] Mark Michalovic, "Tantalum, Congo, and Your Cell Phone," ChemMatters, October 2007, pp. 16-18

[3] E. Williams, "Environmental impacts in the production of personal computers," in Computers and the Environment: Understanding and Managing Their Impacts, R. Kuehr and E. Williams, Eds. Dordrecht: Kluwer, 2003, pp. 41-72

[4] Wikipedia, The Free Encyclopedia ‚Electricity Generation. Available http://en.wikipedia.org/wiki/Electricity_generation [Accessed February 22, 2008]

[5] Wikipedia, The Free Encyclopedia ‚Fossil Fuel. Available http://en.wikipedia.org/wiki/Fossil_fuel [Accessed February 22, 2008]

[6] IAGS, Institute for the Analysis of Global Security, The Future of Oil. Available http://www.iags.org/futureofoil.html [Accessed February 22, 2008]

[7] H. Vesperini, "Congo's coltan rush," BBC News, Aug. 1, 2001. Available http://news.bbc.co.uk/2/hi/africa/1468772.stm [Accessed February 22, 2008]

[8] Wikipedia, The Free Encyclopedia ‚ 2003 Invasion of Iraq. Available http://en.wikipedia.org/wiki/2003_invasion_of_Iraq [Accessed March 2, 2008]

[9]R. Crilly, "Oil from Africa comes with political instability," USA Today, Apr. 30, 2006. Available http://www.usatoday.com/money/world/2006-04-30-africa-oil-usat_x.htm [Accessed March 2, 2008]

 

[10] ITOPF, International Tanker Owner Pollution Federation Limited, Tanker Spill Statistics. Available http://www.itopf.com/information-services/data-and-statistics/statistics/ [Accessed February 22, 2008]

[11] M. Lee, "Our electronic waste is piling up overseas ," San Diego Union Tribune, Jun. 19, 2007. Available http://www.signonsandiego.com/news/state/20070619-9999-1n19ewaste.html  [Accessed March 2, 2008]

[12] Greenpeace, "Toxic Tech: The Dangerous Chemicals in Electronic Products", Greenpeace Briefing, 2008. Available http://www.greenpeace.org/raw/content/international/press/reports/toxic-tech-chemicals-in-elec.pdf [Accessed March 2, 2008]

[13] The National Academic Press, Health Effects of Beryllium Exposure: A Literature Review. Available http://books.nap.edu/openbook.php?record_id=12007&page=1 [Accessed March 2, 2008]

[14] J. Swartzbaugh, J. Sturgill, Univ. of Dayton Reasearcg Institute, Reduction of Arsenic Wastes in the Semiconductor Industry, 1998. Available http://www.epa.gov/nrmrl/pubs/600r02089/600R02089.pdf [Accessed March 2, 2008]

Comments (2)

Anonymous said

at 10:46 pm on Mar 9, 2008

Hi, Guys

Over all you have very good analysis. You connected various different topics effectively, ranging from shift register usage to fossil fuel. I have one suggestion if you want to make this analysis meaning full for future reference. (i.e. After EE 347 class) Instead of using phrases like in experiment (blank) we did this, use phrases that would make sense if to someone who is not aware of the EE 347 context. Other than this minor point your analysis is very good.

- Himanshu

Anonymous said

at 3:23 am on Mar 10, 2008

I liked how you covered the environmental aspects of sustainability since that hasn't been a big part of our labs (outside of sustainability issues in the lab reports). Also, I never knew it took 5 GJ of energy to make a computer! However, after reading that it occured to me that I can't really picture just how much energy 5 GJ really is (I know, I'm a bad engineer). Maybe adding some context could really drive that point home. Also, you talk about how shift registers can operate over a large range of frequency; how does that connect with sustainability? Great analysis though and look at all those sources! Great job.
-T.M.

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