Week #5: (2/19-22) DACs and ADCs

[rjagodowski]

NOTE: Monday, 2/17, is President's Day and all Day & Evening classes are cancelled at STCC on that day. Tuesday, 2/18, follows a Monday schedule, so we will hold our Monday class at the regular time on Tuesday, 2/18.

Today we'll discuss Digital to Analog and Analog to Digital Conversion from the text (Chapter 2.) Ch 2 Handouts here with support from these links from AllAboutCircuits.com. We had covered the material in these handouts previously, so today's lecture will focus on the materials and links present below.

NOTE: The lab for this week's content can be found here. The EWB program is not yet permanently installed on our computers, but select computers will have the program installed during our 12:00-2:30 lab sessions on Thursday, 2/20 and Tuesday, 2/25.

Digital to Analog Conversion

Video Lecture from All About Circuits on Digital to Analog Conversion. (8:28)

Flash Analog to Digital Converter

Ramp Analog to Digital Converter

Successive Approximation ADC

Practical Considerations of ADC Circuits

Here's a good, but brief, Tutorial on Sampling Theory. The math is way beyond our level, but the diagrams give a good physical presentation of what's going when an analog signal is sampled. The "Impulse Train" signal shown represents the process of looking at the signal at period intervals, aka sampling. Multiplying the original analog function by the pulse train creates the outputs shown depending upon the relationship of the spectrum of the analog signal and the sampling frequency. To guarantee all information of the original analog waveform is preserved, the Nyquist Sampling Theorem states that the sampling frequency MUST BE AT LEAST TWICE the highest frequency component of the analog signal. This is where understanding harmonic content of waveforms can be quite important. The next paragraph discusses this harmonic content. As a side note, if you've ever noticed on a video objects such as a wagon wheel or airplane propeller which appears to be turning backwards, or slowly, that is due to UNDERSAMPLING of the video signal. Video signals are commonly sampled at 24 to 30 frames per second, meaning that any object which changes periodically with a frequency greater than 12-15 times per second will experience this undersampling distortion.

As part of our discussion on sampling and quantizing waveforms, we will revisit Falstad.com for some frequency analysis (Spectrum Analysis, aka Fourier Analysis) of what happens to the harmonic content of a waveform when it gets sampled or quantized.