Explain the application and limitations of Milliman's theorem. (IES-06)

Ans.

This theorem provides the equivalent circuits which are either Thevenin's or Norton Equivalent circuits.

This theorem is applicable only their independent voltage sources with their internal series impedances connected directly in parallel, or independent current sources with their internal series admittances connected directly in series.

Limitations:

This theorem is not applicable to circuits where impedances or dependent sources are present between the independent sources.

This theorem is not useful for circuits with less than two independent sources.

What are effects of negative feedback?

Ans.

It stabilizes gain.

Increase BW.

Changes the Ri and R0

Decreases voltage gain, Ad

Decreases harmonic or non-linear distortion.

Decreases effect of input offset voltage at the output

Decreases effect of variation in temperature and supply voltage on the output of the output amplifier

What is noise figure? What is indicates?

Ans. The noise figure (F) is defined as the ratio of the signal-to-noise power supplied to the input terminals of a receiver or amplifier to the signal to- noise power supplied to the output or load resistor.

Noise figure (NF) and noise factor (F) are measures of degradation of the signal-to-noise ratio (SNR), caused by components in a signal chain. It is a number by which the performance of an amplifier or a radio receiver can be specified, with lower values indicating better performance.

What are the problem in the recovery of the baseband signal?

Ans. Suppose that the auxiliary signal used for recovery differ in phase from the auxiliary signal used in the initial translation. If this phase angle is ɵ, the recovered waveform will be proportional to m(t) cos ɵ i.e., amplitude attenuates. Suppose that the recovered baseband signal is not precisely at frequency fc but is instead at fc + ∆f then the recovered baseband signal will be proportional to m(t) cos 2 π∆ ft, resulting a signal which will wax and wane and thus the recovery of the message signal won’t be possible. 

Keep the following in mind when dealing with conversion of parameters in two port networks. These are useful tricks to remember when solving questions for GATE EC or GATE EE.

In series type connections, Z parameters get added.

In parallel type connections, Y parameters get added.

In cascaded type connections, ABCD parameters get multiplied.

In series–parallel type connections, h parameters get added.

In parallel–series type connections, g parameters get added.