QUARTUS II环境下VHDL语言编写DDS程序，双数字信号输出，一为正弦波幅值输出，一正弦波差值信号。时钟2^21HZ，带24bits频率控制字。-QUARTUS II environment, VHDL language DDS program, two digital signal output, an amplitude for the sine wave output, a sine wave difference signal. Clock 2 ^ 21HZ, with 24bi