Facebook
Google
GitHub
Linkedin
logic families
- Thread starter andy146
- Start date
Logic has evolved, it didn't all spring up at once. Early logic families were RTL (resistor transistor logic) and DTL (diode transistor logic). They used low voltages (3.6V) and didn't have very good noise immunity, which created a whole bunch of problems. I stepped into electronics in time to see the end of RTL.
TTL uses 5V ±.25V and has much better noise immunity, is fairly fast, but is very sensitive about its power supply voltage, and is a fairly power hungry. Because so many chips were made TTL is still fairly popular for schools and hobbyists.
ECL came out shortly after for very high speed applications, and is one of the examples of negative logic. Conventional logic has caught up with ECL speeds, but ECL also keeps getting faster. I have seen examples of 40Ghz goggle rates, and much faster has been developed since. As a general logic family it also makes a decent space heater. If you look at ECL internal designs they resemble differential amps, and are a prime example on unsaturated logic. Their on/off voltages are -1.4V and -.6V, and are still in common use for extreme speeds.
CMOS is probably the best for general usage, it has very loose voltage requirements (meaning you can power it up with a large variety of sources), extremely low current needs, and excellent noise immunity. It's speed has crept up nicely over time, which is where we are currently at.
When I was getting into digital (before I went to school) I thought TTL was negative logic, but the gates kept being wrong! An AND gate is a OR gate if you look at it with the voltages reversed, but I was being stupid at the time.
TTL uses 5V ±.25V and has much better noise immunity, is fairly fast, but is very sensitive about its power supply voltage, and is a fairly power hungry. Because so many chips were made TTL is still fairly popular for schools and hobbyists.
ECL came out shortly after for very high speed applications, and is one of the examples of negative logic. Conventional logic has caught up with ECL speeds, but ECL also keeps getting faster. I have seen examples of 40Ghz goggle rates, and much faster has been developed since. As a general logic family it also makes a decent space heater. If you look at ECL internal designs they resemble differential amps, and are a prime example on unsaturated logic. Their on/off voltages are -1.4V and -.6V, and are still in common use for extreme speeds.
CMOS is probably the best for general usage, it has very loose voltage requirements (meaning you can power it up with a large variety of sources), extremely low current needs, and excellent noise immunity. It's speed has crept up nicely over time, which is where we are currently at.
When I was getting into digital (before I went to school) I thought TTL was negative logic, but the gates kept being wrong! An AND gate is a OR gate if you look at it with the voltages reversed, but I was being stupid at the time.
| Thread starter | Similar threads | Forum | Replies | Date |
|---|---|---|---|---|
| M | Mixing Logic Families | Digital Design | 7 | |
| M | Logic Families and Complementary Outputs | Digital Design | 15 | |
|
Why Do We Need a Matched Termination With High Speed Logic Families? | AAC Contributors Forum | 2 | |
| S | Logic families - 5426 v 54LS26 | Digital Design | 9 | |
|
Logic families | Homework Help | 1 |
