Complete Electronics Self-Teaching Guide with Projects

The Output Curve

14 Now it's time to look at the output curve in a little more detail. Take a look at the curve shown in Figure 7.19 for an example.

Figure 7.19

An input signal at the resonant frequency, f_r, passes through a circuit with minimum attenuation, and with its output voltage equal to the peak output voltage, V_p, shown on this curve.

The two frequencies f₁ and f₂ are “passed” almost as well as f_r is passed. That is, signals at those frequencies have a high output voltage, almost as high as the output of a signal at f_r. The graph shows this voltage as V_x.

Signals at frequencies f₃ and f₄ have a low output voltage.

These two frequencies are not passed but are said to be blocked or rejected by the circuit. This output voltage is shown on the graph as V_z.

The output or frequency response curve for a resonant circuit (series or parallel) has a symmetrical shape for a high value of Q. You can make the assumption that the output curve is symmetrical when Q is greater than 10.

Questions

A. What is meant by a frequency that is passed? _____

B. Why are f₁ and f₂ passed almost as well as f_r? _____

C. What is meant by a frequency that is blocked? _____

D. Which frequencies shown on the previous output curve are blocked? _____

E. Does the output curve shown appear to be symmetrical? What does this mean for the circuit? _____

Answers

A. It appears at the output with ...