A nonlinear device that is often used in communication systems is a quadratic memoryless nonlinearity. For such a device if x(t) is the input the output is given as x(1) Amplifier y(1) y(t) = ax(t) + bx(t) Ideal BPF (a) If x(t) = Acos(2 fmt), what is y(t) and Y(f)? (b) If X(f): = Figure 2.11 The system diagram for Problem 2.7. A 0 Ilf-felfm elsewhere (2.88) what is y(t) and Y (f)? (c) A quadratic nonlinearity is often used in a frequency doubler. What com- ponent would you need to add in series with this quadratic memoryless nonlinearity such that you could put a sine wave in and get a sine wave out of twice the input frequency?