Agilent - Evaluating Oscilloscopes to Debug Mixed-Signal Designs

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Introduction

Today's embedded designs based on microcontrollers (MCUs) and digital signal processors (DSPs) often include a combination of analog and digital signal content. Design engineers have traditionally used both oscilloscopes and logic analyzers to test and debug these mixed-signal embedded designs, but a new class of measurement tools known as mixed signal oscilloscopes (MSOs) may offer a better way for you to debug your MCU- and DSP-based designs.


Although MSOs have been on the market for nearly ten years, most engineers have never used one, and many engineers have misconceptions about their benefits and use model. With more oscilloscope vendors introducing hybrid time-domain instruments that merge timecorrelated analog and digital measurement capabilities, it is important that you understand the differences between these instruments and that you are aware of what they can and cannot do.


This paper begins by defining mixed signal oscilloscopes, including an overview of the primary applications where MSOs should be used. This paper discusses the number of channels, bandwidth, and sample rates required to effectively monitor various analog and digital I/O signals in typical MCU/DSP-based designs, as well as covers the various types of mixedsignal triggering you should look for in an MSO in order to effectively test and debug embedded designs. Using an example of a mixed-signal embedded design based on a 16-bitwide instruction-set microcontroller (Microchip PIC18), this paper also provides a typical turn-on and debugging methodology using an MSO to verify proper signal quality of a pulsed analog "chirp" output signal generated by the MCU and its associated peripheral hardware based on a variety of analog, digital, and serial I/O (I2C) input conditions...


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