Experiment: Analog-to-Digital Conversion Study

Topics covered:

- Analog to digital conversion

- Digital to analog conversion

- Sampling

- Quantization

- Converter fidelity

- Binary word

Principles and objectives:

The ADC/DAC model allows your students to progressively study

the basics of converting any type of signal, including sound, by evaluating the influence of various parameters (resolution, sampling frequency) on the quality of signal reproduction.

a) Sampling

Connect a low-frequency generator to the input of the ADC/DAC model and configure a simple periodic signal (triangular), for example,

100 Hz with a maximum amplitude of 5V. Select direct conversion mode (the sampling frequency will then be 20kHz) and set any resolution.

Connect the input and ouExperimentut of the model to direct inputs 1 and 2 of the data acquisition console. In the Scientific Workshop software, start the acquisition to obtain readings of the input and ouExperimentut signals for comparison. It is observed that the sample-and-hold circuit holds the voltage for a measurable duration Te using the pointer tool. This duration is called the sampling period.

b) Quantization

Change the resolution value (2, 4, 8, and 10 bits) and acquire the input and ouExperimentut signals. On the graph, voltage levels are distinguished with a step depending on the set resolution, which is the quantum defining a set of voltage levels. For a blocked input voltage, the closest value belonging to this set of discretized data is determined.

c) Digitization

During digitization, time and voltage are associated with a pair of numerical values. By changing the resolution value, the student understands that it designates the number of bits needed to associate a measured voltage with a numerical value. For 10 bits, the total number of combinations is 1024 (1024=210). A bit is a signal that can take 2 values, 0 or 1. Several bits combined (10 in the case of a 10-bit resolution) form a (binary) word representing these numerical values.

d) A 3.5mm jack microphone can be connected to the input and an 8Ohm speaker to the ouExperimentut to evaluate the fidelity of the conversion based on the resolution

and sampling frequency.

- Model CAN/CNA (ref 185020) - Foxy Console (ref 485000) - A.S. Sup Software (ref 000131) - Microphone (ref 221023) - 10W Protected Speaker (ref 292049)