TABLE OF CONTENTS The concept of mixing is one that most people understand. When you make a cake (even from a box), you take specific materials, mix them together, and end up with a cake. If you mix different-color paints together, you end up with a new color. Both these examples are rather basic, but they illustrate the process of mixing.
Similarly, when you mix together two electronic signals under the right conditions, you end up with a third, different signal (either the sum, the difference, or some combination of the two original signals). For both the cake and the paint, you need to observe certain conditions to make a presentable cake or get even close to the right color of paint. Similarly, certain conditions must be observed when we mix electronic signals.
If you put two signals into an amplifier, you get those two signals at the output (provided they are within the bandwidth of the amplifier and the levels of the signals will not overdrive the amplifier), because the ordinary amplifier is a linear device. That is, when you put an input to the device, you get a signal out that is multiplied by the gain of the device (a 1-V input signal with a gain of 15 ideally results in a 15-V output). Figure 4.26 is a curve of power input versus power output that shows this linear region. The area designated as linear is from the zero point at the lower left corner to the point marked...
