加法器電路的設計

1、9.1.1 級連加法器,結構 由1位全加器級連 優(yōu)點 結構簡單 缺點 延時太長,【例9.1】8位級聯(lián)加法器module add_jl( sum, cout, a, b, cin );output[7:0] sum;output cout;input[7:0] a, b;input cin;,full_add1 f0( a[0], b[0], cin, sum[0], cin1 );full_add1

2、 f1( a[1], b[1], cin1, sum[1], cin2 );full_add1 f2( a[2], b[2], cin2, sum[2], cin3 );full_add1 f3( a[3], b[3], cin3, sum[3], cin4 );full_add1 f4( a[4], b[4], cin4, sum[4], cin5 );full_add1 f5( a[5], b[5], cin5, sum[5

3、], cin6 );full_add1 f6( a[6], b[6], cin6, sum[6], cin7 );full_add1 f7( a[7], b[7], cin7, sum[7], cout );endmodule,1位全加器門級結構原理圖,module full_add1( a, b, cin, sum, cout );input a, b, cin;output sum, cout;wire s1, m1,

4、m2, m3;and ( m1, a, b ), ( m2, b, cin ), ( m3, a, cin);xor ( s1, a, b ), ( sum, s1, cin );or ( cout, m1, m2, m3 );endmodule,8位級聯(lián)加法器RTL圖,9.1.2 并行加法器,結構 用加法運算符描述 由EDA軟件綜合 優(yōu)點 運算速度快,【例9.2】8位并行加法器module

5、add_bx( cout, sum, a, b, cin );output[7:0] sum;output cout;input[7:0] a, b;input cin;assign { cout, sum } = a + b + cin;endmodule,8位并行加法器RTL圖,9.1.3 超前進位加法器,結構 引入超前進位鏈 優(yōu)點 運算速度快,設計思路,1位全加器 SUM = A⊕B

6、⊕Cin = AB⊕(A⊕B )⊕Cin Cout = AB+(A+B) Cin 令 G = AB 進位產(chǎn)生 P = A+B 進位傳輸 則 SUM = G⊕P⊕Cin， Cout = G+PCin,4位全加器 C0 = Cin C1 = G0+P0C0 = G0+P0Cin C2 = G1+P1C1 = G1+P1

7、G0+P1P0Cin C3 = G2+P2C2 = G2+P2G1+P2P1G0+P2P1P0Cin C4 = G3+P3C3 = G3+P3G2+ P3P2G1+P3P2P1G0+P3P2P1P0Cin Cout = C4,【例9.3】8位超前進位加法器module add_ahead( sum, cout, a, b, cin);output[7:

8、0] sum; // 和output cout;input[7:0] a, b;input cin;wire[7:0] G, P; // 進位產(chǎn)生，進位傳輸wire[7:0] C; // 進位,assign G[0] = a[0] & b[0];assign P[0] = a[0] | b[0];assign C[0] = cin;assign sum[0] = G[0] ^ P[0] ^ C[

9、0];assign G[1] = a[1] & b[1];assign P[1] = a[1] | b[1];assign C[1] = G[0] | ( P[0] & C[0] );assign sum[1] = G[1] ^ P[1] ^ C[1];assign G[2] = a[2] & b[2];assign P[2] = a[2] | b[2];assign C[2] = G[1] |

10、 ( P[1] & C[1] );assign sum[2] = G[2] ^ P[2] ^ C[2];,assign G[3] = a[3] & b[3];assign P[3] = a[3] | b[3];assign C[3] = G[2] | ( P[2] & C[2] );assign sum[3] = G[3] ^ P[3] ^ C[3];assign G[4] = a[4] &

11、b[4];assign P[4] = a[4] | b[4];assign C[4] = G[3] | ( P[3] & C[3] );assign sum[4] = G[4] ^ P[4] ^ C[4];assign G[5] = a[5] & b[5];assign P[5] = a[5] | b[5];assign C[5] = G[4] | ( P[4] & C[4] );assign s

12、um[5] = G[5] ^ P[5] ^ C[5];,assign G[6] = a[6] & b[6];assign P[6] = a[6] | b[6];assign C[6] = G[5] | ( P[5] & C[5] );assign sum[6] = G[6] ^ P[6] ^ C[6];assign G[7] = a[7] & b[7];assign P[7] = a[7] | b[7

13、];assign C[7] = G[6] | ( P[6] & C[6] );assign sum[7] = G[7] ^ P[7] ^ C[7];assign cout = G[7] | ( P[7] & C[7] );endmodule,8位超前進位加法器RTL圖,9.1.4 流水線加法器,結構 加入寄存器暫存中間結果 優(yōu)點 提高了系統(tǒng)的運行頻率,精品課件！,精品課件！,三種加法器的