|A Newsletter for the Semiconductor Industry|
Welcome to Tekmos Talks September 2017. In this issue we are going to talk about ROM Design, Inside Tekmos and the solar eclipse, feature a product, and talk about drone technology.
We extend our best wishes to our neighbors along the Gulf Coast. If you would like to help people affected by Harvey please click on the Rebuild Texas image above.
|From the Desk of the President, Lynn Reed|
The Design of a Masked ROM
This is the first in a series of articles covering the design of a masked ROM. It will cover the choices behind making a masked ROM, and the design of the ROM array.
The first question that should be asked is why would anyone ever design a masked ROM when you have flash? It is a good question, and we have two answers. The first is that this ROM is being designed for high temperature applications, and flash memories lose their data at high temperature. Flash memories use stored charge, which will leak away over time. The leakage rate is a function of temperature, and roughly doubles with every 10ºC rise in temperature. A 10-year life at 125ºC reduces to a matter of hours at 275ºC. And that is if the flash is built on a fully depleted SOI CMOS process, which most are not. This reduction in flash lifetime can be partially addressed by frequent refresh operations.
A second reason for considering a masked ROM is that many processes do not support the flash technology, whereas all processes can be used to make a masked ROM.
Once the decision has been made to make a masked ROM, the next choice is the architecture of the ROM array. There are two options: NAND and NOR. NAND has better density, but is slower, and uses more power. NOR has worst density, but is faster and uses less power. In the past, all our ROMs have used the NAND architecture. This time, we opted to use the NOR architecture. At high temperature, everything runs slower. In computer systems, the memory speed is usually the bottleneck, and so it makes sense to design the ROM for maximum speed. Our initial design goal is to have a sub 100 ns access time at 300ºC.
The design of the ROM array is about as simple as possible. Each ROM bit consists of a single N-channel transistor. The source is tied to ground, the gate is connected to the word line, and the drain is connected to the bit lines through the programmable contact. If there is a contact, the bit line goes to zero. If there is no contact, the bit line stays as a one.
The poly word line resembles a transmission line, and it can take the signal a long time to go from one end to the other. We are using a special high temperature process that does not support salicide. As a result, the poly is quite resistive. We address that by running a metal line over the poly, and connect it to the poly every 8 bits. This greatly improves the ROM speed for those bits located the furthest away from the word line drivers.
The next thing that we should worry about is the impedance of the ground lines. This is aggravated by the use of Tungsten as an interconnect metal. We have to use Tungsten because Aluminum has metal migration problems at elevated temperatures. In order to lower the ground impedance, we run perpendicular ground lines every 64 bit lines that convert the ground line from a single stripe into a grid. This allows every ground line in the array to help lower the impedance.
We do have to add additional bits. The initial ROM was an array of 512 rows by 512 columns, for a total of 256K bits. We will group every 8 bit lines together to produce a single output bit. This produces a 64 bit word. To improve reliability, we are adding ECC to the ROM, which will require 7 more output bits, or 56 more bit lines. And we need to add one additional bit line which is always programmed to provide a reference for the self-timing. This will be discussed later.
At this point, I have an array with 512 rows and 569 columns. I will discuss the word lines and their decodes in the next article.
|Inside Tekmos, Lynn Reed|
Tekmos & Solar Eclipse Totality, August 21st 2017
Even though we are 1000 miles from the path of totality, Tekmos decided to send an expedition to check it out. Phil, our test technician, Randy, our graphic artist, and I, rented an RV, and set forth to Tryon, Nebraska (population 157). We chose Tryon, because it was the furthest point from major population centers, and I was paranoid about the possibilities of traffic jams. Tryon does not have much in the way of public accommodations, so we contracted to spend Sunday night in a family's front yard.
None of us had any experience with RVs, but we learned fast. Now I know how burning propane can keep a refrigerator cool, and how to deal with water pumps, generators, and the dreaded black water.
The trip up was uneventful, and we arrived in Tryon as planned, shortly before noon on Sunday, August the 20th. Tryon had made a lot of preparations for the event, and we went to most of them. We went to the TiPi Village, and watched a man make arrowheads. We went to a rodeo, and watched a team penning exhibition. Phil took a trail ride, while Randy and I went to see a sod house, the old bank, and an outdoor jail. Then we went to "Coffee with a Rancher" to discuss raising cattle in the Nebraska sand hills.
The house where we were camped had chickens, goats, and a couple of calves. The son of the owner took us for a trip around the place, and showed us everything, including a box of newborn kittens in the barn. I also learned that there are chickens that laid red, green, and blue eggs. I even had green eggs and ham for my Monday breakfast. This totally surprised me in that I always thought green eggs were a fairy tale from Dr. Seuss. How many other of my cherished beliefs are also wrong?
About an hour before totality, we went over to the viewing area. This was the side of a hill, facing toward the west. The pasture had been mowed, and several benches consisting of boards on hay bales, had been set up. There were perhaps 1,000 people on that hill side. We were concerned about the cloud cover. The sky was totally overcast in the morning. As the day wore on, the clouds began to break up, and we had about 50% cloud cover as we arrived at the eclipse site.
Fifteen minutes before the eclipse, clouds covered the sun, and then they cleared with about 5 minutes to go. Being on a hillside with an excellent view, we could see the shadow of the eclipse race toward us at about 1,000 miles per hour. Then totality happened. This was the most amazing thing I have ever seen. The temperature plunged, and the crowd was shouting for joy. Where we were, totality lasted for 2 and a half minutes.
Then it was over and time to start the 18-hour drive back to Texas.
Tekmos has a 68HC705 design that can be used to replace many variations of the 68HC05 and 68705 microcontrollers. Our first part is the TK68HC05B6 with 6K of ROM. Our second part is the user programmable TK68HC705C8A / TK68HC705C9A devices. These parts use flash memory as contrasted to the original part's One Time Programmable (OTP) EPROM. The 68HC705B16N and 68HC705B32 are available with a longer lead time.
The Tekmos 68HC05 has been carefully designed to duplicate the original 68HC05 on a clock for clock basis. This guarantees complete compatibility with existing code. Even timing loops will work perfectly.
Tekmos is currently seeking customers willing to evaluate our daughtercard-based breadboard in their system for the purposes of design verification.
Below is a list of 68HC705 microcontroller variants that are either available immediately or under development. If you need a version not listed here or have any questions please: Contact Us.
Drone Technology & Uses
Drones are the new technology to cell phones of the 90's with drones for amusement such as the earlier airplane models, drones for farming use, aerial photography, law enforcement, spying, military, search and rescue, and possible delivery of special product orders. Business Insider says of drones four sector major area of use: Military, Commercial, Personal, and Future Technology, "Increasing work efficiency and productivity, decreasing workload and production costs, improving accuracy, refining service and customer relations, and resolving security issues on a vast scale are a few of the top uses drones offer industries globally."
Goldman Sachs predicts military spending will remain the main driver of drone spending in the coming years. They estimate that global militaries will spend $70 billion on drones by 2020. A single US Predator drone costs approximately $4 million, and total spending for the program is estimated at a total of almost $2.4 billion. The impact of commercial drones could be $82 billion and a 100,000 job boost to the U.S. economy by 2025, per AUVSI.
According to airdronecraze, an Amazon Services LLC affiliate advertising program website, drone technology has seven potential generations, and most current technology sits in the fifth and sixth generations.
Here is the breakdown of the technology generations:
|Thank You for Reading Tekmos Talks|
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Tekmos, 20 years of solutions.
Lynn Reed, President
7901 E. Riverside Dr. Building 2, Suite 150