Question

pls answer all and asap.tqvm.

(a) () What is the significant used of multistage amplifier compared to single stage amplifier? (2 marks) (ii) In terms of circuit connection, how to differentiate between direct and capacitively coupled amplifier circuit? (1 mark) (ii) Give a reason why the capacitively coupled amplifier circuit is not suitable for amplifying DC voltage? (2 marks)

Answer 1

Answer a)

(i) The significant use of multistage amplifier compared to single stage amplifier is that the power gain/voltage   gain can be achieved by the single-stage amplifier but it is not enough in practical application. For that, we have to use multiple stages of amplification for achieving the required voltage gain or power. For this purpose multistage amplifier is used.Compared to a single amplifier stage, the multi stage amplifier may have one or more of the following advantages: higher input-output isolation, higher input impedance, higher output impedance, higher gain or higher bandwidth.

(ii)

( b) AC coupling consists of using a capacitor to filter out the DC signal component from a signal with both AC and DC components. The capacitor must be in series with the signal. AC coupling is useful because the DC component of a signal acts as a voltage offset, and removing it from the signal can increase the resolution of signal measurements. AC coupling is also known as capacitive coupling.DC coupling allows both AC and DC signals to pass through a connection. When using DC coupling, no additional capacitor is added to filter the signal.

(iii)

an AC signal, then to eliminate the DC drift in transistors and other components making up the amplifiers, it is more convenient to block the DC signals and let the AC signals go through. So “normally” AC amplifiers use blocking Capacitors and Coupling Transforms in some stage of the amplification and so they cannot be used to amplify DC signals if the DC signals are kept in DC form. If the DC signals are sampled and chopped up into another form as amplitude or frequency or phase-modulated carrier or a pulse duration repetitive signal PWM then the rate of change of the “ adulterated DC signal” will be amplified by an AC amplifier and then will have to be transformed or demodulated back to the pure DC version.