Introduction: How to Design Seven Segment Display Driver Chip on VLSI Consept for the First Time!?
Today, I am going to show you how to design a seven segment display electronic component's driver which is similar with 7447 chip. This project was I did when in my university's last year, thanks to my lecturer, I learned how to desing a chip with Tanner Tools program. With Tanner Eda Tools program, you need to select a technology to produce your chip. I chose 0.25 micrometer as a referance. This means that my technology in this project is 0.25um as well. Actually, we use seven segment displays with 7447 chips to indicate hexadecimal numbers to understand the space which are compund of (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F) as 16 things.
The need list:
1. Your computer
2. Tanner Eda Tools(L-Edit v13.0) Program
3. My university project file (Download it from this step's attachment)
Step 1: What Is Seven Segment Display?
We have got a lot of different seven segment display products. Which may have dots, double segmented and colorful ones. Seven segment displays are very fundamental screen (Or let's call indicators) for us through-out the electronic history. There are seven LEDs included on the surface below and it is different according to common anode or cathode pin. This means you may light LED with common cathode and logic high to anode to illuminate. Or vice-versa.
I shared a table what are the possibilities of seven segments. Check the pictures on this step above.
Step 2: Meaningful Segment Display Signs
This picture shows what I use to indicate 0 to F hexadecimal number with controlling seven segment display's pins. In the picture, you may see | sign means logic high, and X means logic low.
Logic high is 5V or 3.3V is up to your high voltage level; which your technology allows you to must choose what is your high voltage level.
According to my project, there are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 included. To minimize my project enormous-ness to done in short time I had to omit A, B, C, D, E, F these are hexadecimal numbers which equals 10, 11, 12, 13, 14, 15.
On picture 2, there are two type of seven segment display designs in the electronic world generally. These are common-anode and common-cathode.
Step 3: Generic Circuit to Run Seven Segment Display
Before begin to VLSI design, we need to make buttons, resistors, and other basic products included circuit to test how the design will displayed.
According to the picture above, there are two type of display and driver can be seen. In my project, I chose common cathode one to design. If you want, you can choose common-anode, if so, you need to control logic low level instead of logic high level like me. This is up to your design.
Step 4: Tanner Eda Tools
On this program, there some components are available to use such as:
L-Edit --> Layout design
S-Edit --> Schematic design
T-Spice --> Spice analysis
What is the alternative to Tanner Eda Tools is Cadence Virtuoso. Cadence Virtuoso program is very high level designing program for VLSI and Ultra-VLSI consepted chips. With high level programs, it is hard to use Windows to operate the designs. Operating system is also very important when you want to design more efficient and zero errored circuits. Windows everytime shows crashes as blue screen, huhh... Mine sometimes face.
According to the picture, I made a circuits similar with one step ago's circuit.
On S-Edit, I selected N-MOS and P-MOS products to make the circuit quick. This is needed because before you go to chemical side of your chips, you need to show your schematic nodes are working very well. If you couldn't show correct usage of your circuit on Schematic view, it is not true to progress to chemical side of your chip.
Also you need to make voltage and current tests to verify your circuit is well-working, if not, roll back and check every nodes please.
Step 5: Voltage Wave Design
To run your driver's pin to drive your seven segment display, you need to give a voltage level order, and prepare. Look at the picture one, from top to bottom, every piece is for segment's one LED's illumination. When logic level changes seven segment display's LED status changes.
On second picture, I need to tell you that when we keep going with spice analysis our voltage sources pulse period and time is the same on the picture is giving.
Step 6: Using Logic Gates to Preparing Circuit Diagram
With AND Gates, OR Gates, and NOT Gates using is for doing the circuit with logic gates.
This is our referance to proceed with N-MOS and P-MOS products.
While I am using mos technology for logic gate aliasing, there are bulk pins important. N-MOS's bulk pin should go to minimum logic level of voltage and P-MOS's bulk pin should go to maximum logic level of voltage in the circuit. So, on chemical side also, you need to draw bulk pins.
Step 7: T-Spice Settings and Netlist
Prepare netlist as picture 1.
Prepare voltage sources as picture 2. This is very important to switch when. Because it alters the situation of your driver as your circuit.
Step 8: Layout Draw
According to the picture, on Tanner Eda Tools L-Edit, these are necessary things that we need to use to produce N-MOS and P-MOS products to make them logic gates.
There are three pictures on the attachment. These are NOT-GATE, AND-GATE, OR-GATE. On first picture, we need to use them all to produce logic gates as fundamental three of them; not, and, or.
I uploaded a full layout design of mine to show you how hard it is. Not hard, but need some time to do.
Step 9: How About the Dimention of Layout Chemical Drawing?
Since my technology is 0.25um, the space of chip fits to 13.41 mm2 area. This means, the core of chip is approx. 13.41mm2 big.
Lower technology lower area needs.
Step 10: How About the Power Consuption of the Core Circuit?
Power = voltage x ampere
So, within 10ms period here is the graphic of power consuption of core circuit.
Core circuit means there is only working circuit which didn't have chip pad and dresses, for example, to seem with legs to put it onto bread board. This is just a tiny circuit we have.
Step 11: Symbolic Schematic Dress of the Circuit
We have four pins to set the logic input for changing display's meaningful numbers.
We have seven pins out to the seven segment display to illuminate common cathoded LEDs.
Also, our circuit's energy comes from left sided voltage source which is stable source for us as need.
Step 12: To Sum Up
Now, we have got VLSI consept design of seven segment display driver.
The 6 and 9 signs didn't have complete sign, because my referance of driver chip is like that. There is very different type of drivers to run seven segment displays.
NOTE: This project is my life's first time project to produce a chip to do something. I hope, you understand well.
That's all !