数字正交调制基础mixed signal Fundamentals of Digital Quadrature Modulation How a formerly analog-only application, the quadrature modulator, is finding a home in modern digital CMOS fabrication techniques By Ken Gentile denoted by the symbol fc (or ωc for radian frequency) throughout this text. Typically, fc is much higher in frequency than the highest frequency component of the message signal. The Basics The concept of modulation comes from the trigonometric identity: cos (x )cos (y) = 1 1 cos (x + y) + (x y) 2 2 T he concept of modulation is not at all new, it has been around since the early days of radio. Modulation, especially in the context of RF applications, refers to the mixing of two sinusoidal signals. One signal is the message signal and contains the information to be modulated. It usuall……