Example 1.5


Question 1.10


In-depth

 

The vector modulator

The arrangement of mixers and a combiner (summing device) shown here forms an extremely useful building block in digital communications systems. It achieves a linear frequency translation of all components in the input signal (represented by its in-phase and quadrature components) by a carrier frequency component (also represented by its in-phase and quadrature components). This building block is often referred to as a vector modulator or quadrature modulator and, as we shall see, can be used for both frequency up-conversion and down-conversion.

The output of the two mixing processes is given by:

and  

which when subtracted from each other result in a single up-converted component:

and when summed give a down-converted component: