Question

Q11: What is Sample and Hold Scheme.? Q12: Explain what is Modulation index and why is it important characteristic of AM.?

Answer 1

1. Sample and hold circuit is electronics device in which input voltage given to device in form of samples means input given and then hold input and then repeated it again and again.

The time when input voltage given to circuit, is known as sampling time.

The time for which input signal is hold and no signal come in circuit is known as holding time.

Capacitor is the heart of this circuit as it has properties to charge when AC voltage given and then discharge. Which is required to produce sample and hold output.

This circuit consists of Two OP AMPs, one capacitor and on evonyrol circuit. Circuit diagram also shown in attached photo.

In this device input voltage given at first OP AMP and then there are a switch which is controlled by a control circuit. Switch ON and OFF time is decided by this control switch accord to required sample signal at output.

When switch is closed then sampling process come in effect snd when switch is opened then holfing effect comes. With this with proper setting of capCitor and control signal we can acheive required signal at output.

Switch Ist op-Amp Analog and op - Amy Input Analog output - € Holding Capacitor Contacto signal Circuit diagram of sample and Hold circuit

Applications of sample and hold circuits:

1. Analog to digital converters

2. digital interface circuits

3. Analog demultiplexers

4. Data distribution systems

5.Pulse modulation systems etc.

2) Modulation index is a measure of extent of modulation done on a carrier signal.Always strength of carrier signal must be more than modulated or information signal.Its very important part in AM,FM and PM signals.Modulation index is very important to determine strength and quality of transmitted signal.

Amplitude modulation, it is defined as the ratio of the amplitude of modulating signal to that of the carrier signal.

m=Ac/Am

Where Ac is amplitude of carrier signal and Am is amplitude of modulated or information signal.

Its value is kept less than 1 to avoid overmodulation which leads to distortions in the modulated signal and makes it very hard to demodulate and extract the modulating signal.

Its also important for power calculations of main and sideband signals and overall power of signal.

Total power = Carrier power{1+(m​​​​​​2​​​​​/2)}