Optimized ALU with BIST Implementation using Encounter Platform

March 10, 2019 Critical Thinking

Optimized ALU with BIST Implementation using Encounter Platform.D M Srinivas
Assistant Professor
E&E Dept, PESCE Mandya
Srinath M S
Assistant Professor
E&E Dept, PESCE Mandya
Lokesh T R
Assistant Professor
E&E Dept, PESCE Mandya
Karthik N S (M.tech)
PESCE Mandya
Email:[email protected]
Abstract— This paper provides an Optimized Arithmetic Logical Unit (ALU) with BIST capability , ALU comprising of different airthemetic operations and logical operations is implemented. ALU is used in many processing and computing devices, due to rapid development of technology not only the faster arithmetic unit is required but also less area and low power arithmetic units are needed and due to the increasing integration complexities of IC’s the Optimized ALU implemented sometimes may mal-function, so testing capability must be provided and this is accomplished by Built In Self Test (BIST) for Optimized ALU. In this project the implementation will be done in Encounter platform.

Airthemetic Logic Unit (ALU) is an important and necessary unit present in every processors and all computing devices performing airthemetic operations like addition, subtraction, multiplication, increment,decrement,shifting and logical operartions like and, or, not, exor. The ALU must be optimized and when manufactured they might have defects or might be faulty hence to increase testability Design For Testability(DFT) must be provided one such methodology is Built-In-Self-Test (BIST). BIST technique provides little cost, a well-defined increase in the testability of the Circuit Under Test (CUT). The test pattern generator is a part of BIST implemented using Linear feedback Shift Register (LFSR) , this increases the testability of ALU.

Proposed Method and Implementation
Optimized ALU implementation for increasing speed and decreasing power and delay, fast adder like Carry Save Adder is implemented and fast multiplier like Vedic multiplier one of the vedic techniques is implemented , by using particular adder and multiplier units area, power and delay optimization is achieved in ALU.

243205466090BIST uses test pattern generators to generate test patterns then these test patterns are applied to circuit under test that is ALU and the output is analyzed and the functionality is tested.

Fig1:ALU Architecture
Using carry save addition, the delay can be reduced. The methodology is to take 3 numbers that we want to add together, x + y + z, and convert it into two numbers c + s such that x + y + z = c + s, will be computed in short time. In carry save addition, we directly pass carry to final step.

Fig2:CSA addition
Fig3:CSA Architecture
Fig4: Comparision of adders
Subtraction: The 2’s Complement Addition technique is used for subtraction, as adder block is optimised using carry save adder ,subtraction unit is also optimised.

Multiplier unit is optimized using Vedic Multiplier technique this increases speed and decreases power.

Fig5:Mutiplier Representation

Fig6:2×2 Multiplier hardware representation
Fig7:4 bit multiplier

Fig8:8bit Multiplier

Fig9:16 bit multiplier

Fig10:32 bit multiplier
Multiplier area and delay395605111125
Fig11: Optimized ALU
After designing and implementing Optimized ALU , BIST has to be implemented, the diagram of BIST is as shown in the diagram, it has BIST controller which selects whether it should work either in testing mode or normal mode ,it has test pattern generators like LFSR linear feedback shift register which generates test patterns these test patterns are applied to circuit under test that is optimized ALU over here then the result obtained is analysed and checked for correctness of ALU. LFSR is an n-bit shift register which randomly produces test vectors till 2n-1 very quickly due to minimum usage of combinational
logic. The usage of exclusive-OR gates and shift register produces binary sequence at each flip-flop. By proper selection of points at which we take the feedback from an n -bit shift register we can produce a PRBS of length 2n – 1, that includes all possible patterns of n bits, in which all-zeros pattern is excluded. In an LFSR, the bits at selected positions of shift register are fed back into the register’s input bit.


Fig12: BIST
In this paper we have implemented Optimized ALU with BIST capability which has lesser area,power and delay implemented using carry save adder and vedic multiplier with testing capability provided by Built in Self Test provides testing capability.

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