Full custom digital ic design of priority encoder

The enhancement on a simple encoder circuit, in terms of handling all possible input combinations has lead to the development of special circuits known as Priority Encoders. These circuits facilitate in compressing several inputs into numerous small outputs. The quality feature of these encoders is encoding the inputs just to make sure that only highest order lines are encoded. The result or output of the priority encoder should be a binary representation of ordinal numbers articulated in BCD format. In addition, these also manage interrupt requests through high priority request. Whenever there is more than one active input at same time, then highest priority input will be given more preference. One can find priority encoders in standard or normal IC form such as TTL 74LS147 or TTL 74LS148. Basically, the former encodes 9 datelines to 4 lines as in (8-4-2-1) BCD. And the latter expresses 8 datelines to 3 lines as in 4-2-1 (octal) binary. In order to provide octal expansion with no requirement of external circuitry, one needs Cascading Circuitry. Data inputs and data outputs are active even at low levels. Priority encoders find wide range of applications as in keyboard encoding, range selection,
Bit level encoding, code converters and generators.

1. Full Custom Digital IC Design of Priority Encoder 74LS 147 & 148 Team members Bhargav-l401 Srikanth-452 Venkatesh-459 Vishesh Thakur Singh-460

2. What is an “Encoder” An   encoder  is a device or a combinational circuit that   converts  information from one format or  code  to another.  Digital Encoder  are more commonly called a  Binary Encoder   takes all  its data inputs one at a time and then converts them into a single encoded output.  An "n-bit" binary encoder has 2 n  input lines and n-bit output lines 

3. 4 to 2 encoder

4. Priority Encoder: A   priority encoder   is a special type of encoder whose output corresponds to the currently active input which has the highest priority. So when an input with a higher priority is present, all other inputs with a lower priority will be ignored.

5. Types of Priority Encoders (a) IC SN54/74 LS147 (b) IC SN54/74 LS148 8-to-3 bit priority encoder 10-to-4 bit priority encoder

6. 8 to 3 priority encoder

7. Functional Block Diagram of 74LS148 Output A0=∑(1,3,5,7) Output A1=∑(2,3,6,7) Output A2=∑(4,5,6,7)

8. 10 to 4 priority encoder 10 X 4 Priority Encoder Lowest priority Highest priority D0 D9 Y0 Y1 Y2 Y3

9. Functional Block Diagram of 74LS147

10. 8 X 3 Priority Encoder Schematic View Symbol view

11. Verifying Functionality of 74LS147

12. Schematic view of 10 X 4 Priority encoder

13. Symbol of 74LS147

14. Functional Verification of 74LS148

15. Layout of 74LS148

16. Layout of 74LS147

17. Applications Keyboard Encoder Interrupt Requests Positional Encoders

18. Priority Encoder Navigation

19. Targets achieved S.No : Specifications: Value(74LS148) Value(74LS147) 1. Technology 180nm 180nm 2. Supply ( Vdd ) 1.8v 1.8v 3. Area 62.26 um. x 283.15 um. 76.97 um. x 279.2 um 4. Power without Parasitics (w) 5.69809658e -07 -1.0852728e -05 5. Power with Parasitics (w) 2.1360425e -06 -8.6488442e -07

20. Future Scope 16-to-4 Priority Encoder:- As many as 16 interrupts can be serviced based upon their priority

21. Thank You