Question 11.10: Phase Distortion Suppose that the input signal given by vi(t...
Phase Distortion
Suppose that the input signal given by
vi(t) = 3 cos(2000πt) – cos(6000πt)
is applied to the inputs of three amplifiers having the gains shown in Table 11.2. Find and plot the output of each amplifier.
Table 11.2. Complex Gains of the Amplifiers Considered in Example 11.10
| Amplifier | Gain at 1000 Hz | Gain at 3000 Hz |
| A | 10\angle 0^\circ | 10\angle 0^\circ |
| B | 10\angle -45^\circ | 10\angle -135^\circ |
| C | 10\angle -45^\circ | 10\angle -45^\circ |
Applying the gains and phase shifts to the input signal, we find the output signals for the amplifiers to be
v_{oA}(t)=30\cos{(2000\pi t)}-10\cos{(6000\pi t)}
v_{oB}(t)=30\cos{(2000\pi t-45^\circ)}-10\cos{(6000\pi t-135^\circ)}
v_{oC}(t)=30\cos{(2000\pi t-45^\circ)}-10\cos{(6000\pi t-45^\circ)}
Plots of the output waveforms are shown in Figure 11.27. Amplifier A produces an output wave form identical to the input, and amplifier B produces an output wave form identical to the input, except for a time delay. For amplifier A, the phase shift is zero for both frequency components, whereas the phase shift of amplifier B is proportional to frequency. (The phase shift for the 3000-Hz component is three times the phase shift for the 1000-Hz component.) Amplifier C produces a distorted output wave form because its phase response is not proportional to frequency.
