By: Nitesh kumar (081130) Sharad Rastogi (081131) Aditya Khandelwal (081132) E-5 Batch

Digital Communication Project

Aim:

To design a flat top sampling circuit.

Apparatus used:

IC LF 398, resistors, capacitors, bread board, CRO, power supply, connecting wires, BNC cables, function generator.

Circuit diagram:

Pin Diagram: IC LF 398

Theory:

A very common, and easily implemented method of sampling of an analog signal uses the sample-and-hold operation. This produces flat top samples.

Flat top sampling takes a slice of the waveform, but cuts off the top of the slicehorizontally. The top of the slice does not preserve the shape of the waveform.

After an analogue waveform is sampled in the analogue-to-digital conversion process, the continuous analogue waveform is converted into a series of pulses whose amplitude is equal to the amplitude of the analogue signal at the start of the sampling process. Since the sampled pulses have a uniform amplitude, the process is called flat top sampling. Alternatively, in a process called natural sampling, the amplitude of the sampled pulse is allowed to vary with the amplitude of the analogue waveform as it changes during the sampling period.

In flat top sampling the electronic circuit required for sampling are less complicated as compared to the one used in natural sampling, at demodulation of the sample it is very difficult to maintain the natural waveform of the natural sampling so flat top sampling can easily be demodulated.

Result:

Sampled wave was obtained successfully.

Applications:

1) Speech sampling:

Speech signals, i.e., signals intended to carry only human speech, can usually be sampled at a much lower rate. For most phonemes, almost all of the energy is contained in the 5Hz-4 kHz range, allowing a sampling rate of 8 kHz. This is the sampling rate used by nearly all telephony systems, which use the G.711 sampling and quantization specifications.