What is mixed signal testing? In the early days of mixed signal devices, mixed signal testing meant testing an A/D or D/A converter or a track–and–hold device. With the advent of digital signal processing (DSP) techniques for device testing in the 1970s and 1980s, mixed signal testing became a more general way to generate and measure analog signals with digital processing of the resulting data. The use of DSP techniques with A/D and D/A conversion is the essence of creating fast, repeatable and accurate test programs for mixed signal devices.
 

• The components of a mixed signal test sytem
• The mathematical basis of DSP
• The principles of analog signal theory
• The basics of sampling theory and how to correctly sample an analog signal
• How to create an analog signal for a DUT with a waveform generator
• How to connect a DUT so that analog and digital signals do not interfere with each other
• Why and when analog filtering and other conditioning is necessary
• Typical DSP algorithms and when and how they should be used
• How to extract test measurements from sampled data and relate them to device specifications

This training course has a hidden agenda—to help you learn to "think analog". Analog device design and testing has a distinctly different philosophy from its digital counterpart. In digital, the general thought is "If I deliver exactly this input stimulus, I get exactly that output result". In analog, it is more akin to "If I deliver exactly this input stimulus, I should get an output within this range if it doesn’t oscillate". Analog measurements and limit comparisons decide not if a device is exactly right, but if it is good enough. Learning to "think analog" will help you be more comfortable with this concept and make it easier for you to move into the world of mixed signal testing.

Two devices are used as the primary examples for DSP testing. They are a D/A converter and an A/D converter. Although there are many mixed signal device types, these are chosen for several reasons:

1. The output signal from a D/A is an analog signal which could be from any analog circuit. Thus the knowledge basis and techniques used to measure its parameters could be used to measure any analog signal.
2. An A/D converter has an analog input, digital inputs and digital outputs. It requires synchronous conversion timing and output data collection plus DSP analysis of output results. It requires input signal filtering and conditioning and may have an input multiplexer or track and hold built in.
3. The equipment training classes given by automatic test equipment manufacturers often use data converters as their example devices. This prepares you to learn more about the equipment by already knowing the fundamental principles of data converters.
    

This course reference manual and its accompanying software laboratory were written for the training course "Fundamentals of Mixed Signal Testing" taught by Soft Test Inc. It contains text and figures which present a wide variety of real world experience in mixed signal design, manufacture and testing. The math, although substantial, is presented in a way that will not intimidate those of you who have not seen it in a while (or ever). Thought provoking questions and lab exercises are interspersed throughout the material. Answers to questions are at the end of each chapter.

To assist in understanding the material, software laboratory experiments are included to demonstrate the concepts of Fourier series, sampling theory, waveform generation, waveform sampling, coherency and time and frequency graphing. The software uses Fast Fourier Transform and Inverse Fourier Transform algorithms and simulates a real oscilloscope and spectrum analyzer. It attempts to graphically illustrate the concepts while being fun to use, and is also useful for developing device tests.

Note: The purely digital aspects of mixed signal testing are not covered in detail in this course. If you need to learn about digital vector patterns, timing edge measurement, VOL or VOH tests, etc., please look into Soft Test’s course on The Fundamentals of Digital Semiconductor Testing or CD–ROM computer based training course on Semiconductor Testing.
 

This course has Microsoft Windows based interactive laboratory exercises which demonstrate the principles of sampling, Fourier series, sinusoidal waveforms, FFT type Fourier transforms, inverse FFT, signal generation and other mixed signal testing concepts. When you take this course from Soft Test, every 2 students will share a laptop computer system to do the lab work.

The interactive DSP Lab software requires a computer system with the following characteristics:

80486 or higher CPU
24 Meg RAM
Windows 95, Windows 98, Windows NT 4 or higher operating system
550K bytes hard disk space