Download Presentation
## Logical Circuits

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**1. **Logical Circuits Philip Gebhardt
3/15/2011

**2. **Logic Circuits
Negative, Positive, and Complimentary circuits
Logic Gates
Programmable Logic Devices

**3. **Logic Circuits are built from Transistors Transistors act as the switches in circuits
Controlled by a logical signal from another logic circuit
The most popular transistor used today
The metal oxide semiconductor field-effect transistor (MOSFET)
Two different types: n-channel (NMOS) and p-channel (PMOS)

**5. **NMOS Realization of a NOT gate

**6. **NMOS Realization of the NAND gate

**7. **NMOS Realization of the AND gate

**8. **NMOS Realization of the AND gate

**9. **NMOS Realization of the NOR gate

**10. **NMOS Realization of the OR gate

**11. **Complementary MOS (CMOS)

**12. **Logic Devices
7400 Series Standard Chips
Programmable Logic Devices
Programmable Logic Array (PLA)
Programmable Array Logic (PAL)
Complex Programmable Logic Devices (CPLDs)

**13. **Logic Devices 7400 Series Standard Chips and all other Logic Devices measured in NAND equivalency gates

**14. **Logic Devices 7400 Series Standard Chips and all other Logic Devices measured in NAND equivalency gates
Ex: The macrocells in PALs are often about 20 equivalent NAND gates

**15. **7400 Series Standard Chips External pins used as input/ouput
Two pins used for VDD and GND leads
Multiple chips with different logical gates can be connected to realize logical functions

**16. **F = X1X2 + X2’X3

**17. **Not very efficient for operations with large logical capacity
Mostly used today as buffers from other logical circuits

**18. **Programmable Logic Devices PLDs are general-purpose computer chips designed to implement logical circuits.
Devices with a lot of circuitry and logical gates
Unlike 7400 series chips, has Non-fixed structure
Can be considered a black box with wide range of logical combinations
Programmable Logic Array (PLA)
Programmable Array Logic (PAL)

**19. **PLD as a Black Box

**20. **Programmable Logic Arrays (PLAs) PLAs can be broken down into two planes of wires which pass logic gates
AND plane: logic variables (and their compliments) pass through the AND gates
OR plane: the resultants from the AND gates then pass through the OR gates
Switches programmed by the user determine which variable pass through which gates

**21. **Generic PLA

**22. **PLA Implementation

**23. **Programmable Array Logic Unlike PLAs, PALs are not fixed on both logical planes
Generally only the AND plane fixed
Less flexibility but more cost efficient and better performance
Uses extra circuitry after OR gates for more versatility
Macrocells
Flip-flops, MUXs, more buffers

**24. **PAL Structure

**25. **Example of macrocell

**26. **Benefits Limitations of PLAs and PALs PLAs
Efficient for the area needed for implementation
Too many switches decreases performance and increases costs for manufacturing
PALs
Less expensive and easier to manufacture compared to PLAs
Macrocells allow for implementation of logical circuits with multiple levels or phases
Less flexibility requires extra circuitry