Type of Adders with Verilog Code

Addition on 2 -bit  ->

d_out[1:0] =  a_in + b_in ;

Half Adder ->

Full Adder -->

Verilog Code ->

Half Adder -> 

module half_adder(a,b,sum,carry);

input a,b;

output sum, carry;

wire sum, carry;

assign sum = a^b; // sum bit

assign carry = (a&b) ;

endmodule

Types of Adders :

1. Ripple Carry Adder 
2. Carry Lookahead Adder
3. RCLA (Ripple block carry lookahead adder)
4. BCLA (Binary carry lookahead adder)
5. conditional sum adder 
6. carry select adder 
7. carry skip adder 

    8.Parallel prefix adder -

• Ladner-Fischer adder
• Kogge-Stone adder
• Brent-Kung adder
• Han-Carlson adder

Ripple Carry Adder -> 

The most straightforward implementation of a final stage adder for two n-bit operands is a ripple carry adder, which requires n full adders (FAs). The carry-out of the ith FA is connected to the carry-in of the (i+1)th FA. Figure 1 shows a ripple carry adder for n-bit operands, producing n-bit sum outputs and a carry out. 

Verilog Code for Ripple carry Adder - 

-------------------------------------------------------------------- VERILOG CODE --------------------------------

module ripple_carry_adder ( 

 input [n-1:0] A_in,

 input [n-1:0] B_in,

 output [n-1:0] Sum,

 output Cn 

);

parameter n =10;

full_adder i_full_adder_0 ( .A(A_in[0] , .B(B_in[0], .sum(sum[0]) , .cin(1'b0), .cout(carry[0]) );

genvar c;
generate
for(c=1 ; c < n ; c = c +1) begin

  full_adder i_full_adder[c] ( .A(A_in[c]),
  .B(B_in[c]),
  .sum(sum[c]),
  .cin(carry[c-1]) ,
  .cout(carry[c])
  );
end

endgenerate

endmodule
-------------------------------------------------------------------- VERILOG CODE End -------------------------

Carry Lookahead Adder

 ---- Ref ---
 http://www.aoki.ecei.tohoku.ac.jp/arith/mg/algorithm.html#fsa_pfx

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