NATIONAL COLLEGE OF SCIENCE & TECHNOLOGY Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite EXPERIMENT 2 DIGITAL COMMUNICATION OF ANALOG DATA USING PULSE-CODE MODULATION (PCM)Ramos, Mary Grace C. September 20, 2011Signal Spectra and Signal Processing/BSECE 41A1 Score: Engr. Grace Ramones Instructor
OBJECTIVES: 1. Demonstrate PCM encoding using an analog-to-digital converter (ADC). 2. Demonstrate PCM encoding using an digital-to-analog converter (DAC) 3. Demonstrate how the ADC sampling rate is related to the analog signal frequency. 4. Demonstrate the effect of low-pass filtering on the decoder (DAC) output.
SAMPLE COMPUTATION:Sampling frequencyFrequencyCut-off frequency
CONCLUSION: Pulse-code modulation (PCM) consists of the conversion of a series of sampledanalog voltage levels into a sequence of binary codes, with each binary number that isproportional to the magnitude of the voltage level sampled. Translating analog voltagesinto binary codes is called A/D conversion, digitizing, or encoding. The device used toperform this conversion process called an A/D converter, or ADC. It is observed after the experiment that the measured sampled frequency has thesame value as the frequency generator. But the sampling frequency is more than twicethe value of the sampling frequency. While, as compared to the Nyquist frequency, it istwice the highest value of the sampling frequency. After filtering, there is no change observed in the DAC output. The filteredoutput is observed to be closely similar to the representation of the analog inputwaveshape. The ADC conversion time puts a limit on the sampling rate because the nextsample cannot be read until the previous conversion time is complete. The samplingrate is important because it determines the highest analog signal frequency that can besampled. In order to retain the high-frequency information in the analog signal actingsampled, a sufficient number of samples must be taken so that all of the voltage changesin the waveform are adequately represented. Because a modern ADC has a very shortconversion time, a high sampling rate is possible resulting in better reproduction ofhigh frequency analog signals.