DSP Tutorial

Digital Signal Processor (DSP)

A Digital Signal Processor is a special-purpose CPU (Central Processing Unit) that provides ultra-fast instruction sequences, such as shift and add, and multiply and add, which are commonly used in math-intensive signal processing applications.

DSPs are not the same as typical microprocessors though. Microprocessors are typically general purpose devices that run large blocks of software. They are not often called upon for real-time computation and they work at a slower pace, choosing a course of action, then waiting to finish the present job before responding to the next user command. A DSP, on the other hand, is often used as a type of embedded controller or processor that is built into another piece of equipment and is dedicated to a single group of tasks. In this environment, the DSP assists the general purpose host microprocessor.

Digital Signal Processing

Digital Signal Processing is a technique that converts signals from real world sources (usually in analog form) into digital data that can then be analyzed. Analysis is performed in digital form because once a signal has been reduced to numbers, its components can be isolated, analyzed and rearranged more easily than in analog form.

Eventually, when the DSP has finished its work, the digital data can be turned back into an analog signal, with improved quality. For example, a DSP can filter noise from a signal, remove interference, amplify frequencies and suppress others, encrypt information, or analyze a complex wave form into its spectral components.

This process must be handled in real-time – which is often very quickly. For instance, stereo equipment handles sound signals of up to 20 kilohertz (20,000 cycles per second), requiring a DSP to perform hundreds of millions of operations per second.

Types of DSPs

Because different applications have varying ranges of frequencies, different DSPs are required. DSPs are classified by their dynamic range, the spread of numbers that must be processed in the course of an application. This number is a function of the processor’s data width (the number of bits it manipulates) and the type of arithmetic it performs (fixed or floating point). For example, a 32-bit processor has a wider dynamic range than a 24-bit processor, which has a wider range than 16-bit processor. Floating-point chips have wider ranges than fixed-point devices.

Each type of processor is suited for a particular range of applications. Sixteen-bit fixed-point DSPs are used for voice-grade systems such as phones, since they work with a relatively narrow range of sound frequencies. Hi-fidelity stereo sound has a wider range, calling for a 16-bit ADC (Analog/Digital Converter), and a 24-bit fixed point DSP. Image processing, 3-D graphics and scientific simulations have a much wider dynamic range and require a 32-bit floating-point processor.

Uses

DSP chips are used in sound cards, fax machines, modems, cellular phones, high-capacity hard disks and digital TVs. According to Texas Instruments, DSPs are used as the engine in 70% of the world’s digital cellular phones, and with the increase in wireless applications, this number will only increase.Digital signal processing is used in many fields including biomedicine, sonar, radar, seismology, speech and music processing, imaging and communications.

Market

According to Forward Concepts, the DSP chip market was estimated to be $17.6B in 2007.

Additional sources of information*

Bores Signal Processing – Intro to DSP
What is.com – digital signal processing

Companies providing DSPs

• AnalogDevices
• Texas Instruments
• Motorola

* The WAVE Report is not responsible for the content of external sites