加法器电路的设计

1、n 应用 数字信号处理和数字通信 n 地位 影响系统的运行速度 n 实现 l 级联加法器 l 并行加法器 l 超前进位加法器 l 流水线加法器 9.1.1 级连加法器 l 结构 由1位全加器级连 l 优点 结构简单 l 缺点 延时太长 1位 全加器 a0 b0 sum0 cin 1位 全加器 a1 b1 sum1 cin1 1位 全加器 a7 b7 sum7 cin7cout 【例9.1】8位级联加法器 module add_jl( sum, cout, a, b, cin ); output7:0 sum; output cout; input7:0 a, b; input cin; ful

2、l_add1 f0( a0, b0, cin, sum0, cin1 ); full_add1 f1( a1, b1, cin1, sum1, cin2 ); full_add1 f2( a2, b2, cin2, sum2, cin3 ); full_add1 f3( a3, b3, cin3, sum3, cin4 ); full_add1 f4( a4, b4, cin4, sum4, cin5 ); full_add1 f5( a5, b5, cin5, sum5, cin6 ); full_add1 f6( a6, b6, cin6, sum6, cin7 ); full_add1

3、f7( a7, b7, cin7, sum7, cout ); endmodule 1位全加器门级结构原理图 a b sum cout c s1 m1 m2 m3 module full_add1( a, b, cin, sum, cout ); input a, b, cin; output sum, cout; wire s1, m1, 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

4、8位级联加法器rtl图 9.1.2 并行加法器 l 结构 用加法运算符描述 由eda软件综合 l 优点 运算速度快 【例9.2】8位并行加法器 module add_bx( cout, sum, a, b, cin ); output7:0 sum; output cout; input7:0 a, b; input cin; assign cout, sum = a + b + cin; endmodule 8位并行加法器rtl图 9.1.3 超前进位加法器 l 结构 引入超前进位链 l 优点 运算速度快 l 设计思路 n 1位全加器 sum = a b cin = ab (a b ) ci

5、n cout = ab+(a+b) cin 令 g = ab 进位产生 p = a+b 进位传输 则 sum = g p cin， cout = g+pcin n 4位全加器 c0 = cin c1 = g0+p0c0 = g0+p0cin c2 = g1+p1c1 = g1+p1g0+p1p0cin c3 = g2+p2c2 = g2+p2g1+p2p1g0+p2p1p0cin c4 = g3+p3c3 = g3+p3g2+ p3p2g1+p3p2p1g0+p3p2p1p0cin cout = c4 【例9.3】8位超前进位加法器 module add_ahead( sum, cout, a

6、, b, cin); output7:0 sum; / 和 output cout; input7:0 a, b; input cin; wire7:0 g, p; / 进位产生，进位传输 wire7:0 c; / 进位 assign g0 = a0 assign p0 = a0 | b0; assign c0 = cin; assign sum0 = g0 p0 c0; assign g1 = a1 assign p1 = a1 | b1; assign c1 = g0 | ( p0 assign sum1 = g1 p1 c1; assign g2 = a2 assign p2 = a2

7、| b2; assign c2 = g1 | ( p1 assign sum2 = g2 p2 c2; assign g3 = a3 assign p3 = a3 | b3; assign c3 = g2 | ( p2 assign sum3 = g3 p3 c3; assign g4 = a4 assign p4 = a4 | b4; assign c4 = g3 | ( p3 assign sum4 = g4 p4 c4; assign g5 = a5 assign p5 = a5 | b5; assign c5 = g4 | ( p4 assign sum5 = g5 p5 c5; assign g6 = a6 assign p6 = a6 | b6; assign c6 = g5 | ( p5 assign sum6 = g6 p6 c6; assign g7 = a7 assign p7 = a7 | b7; assign c7 = g6 | ( p6 assign sum7 = g7 p7 c7; assign cout = g7 | ( p7 endmodule 8位超前进位加法器rtl图 9.1.4 流