Signals and Systems of 3 Familiar Devices
You probably have some level of familiarity with consumer electronics, such as MP3 music players, smartphones, and tablet devices, and realize that these products rely on signals and systems. But you may take for granted the cruise control in your car.
Here, the signals and systems framework in three familiar devices are shown at the block diagram level — a system diagram that identifies the significant components inside rectangular boxes, interconnected with arrows that show the direction of signal flow. The block diagram expresses the overall concept of a system without intimate implementation details.
Signals and systems are operating in all the major peripherals of the MP3 player — even in the processor.
In reality, signals are in every part of the system, but pure digital signals are excluded in this example, so memory is not addressed. The processor runs an operating system (OS); under that OS, tasks perform digital signal processing (DSP) algorithms for streaming audio and image data.
All the peripheral blocks (the blocks that sit outside the processor block) contain a combination of continuous- and discrete-time systems. You stream digital music in real time from memory in a compressed format. The processor has to decompress the audio stream into signal sample values (a discrete-time signal) to send to the audio codec. The audio codec contains a digital-to-analog converter (DAC) that converts the discrete-time signal to a continuous-time signal.
The Wi-Fi and Bluetooth radios (blocks with antennas) interface to the processor with digital data but interface to the antenna by using a continuous-time signal at a frequency of 2.4 GHz. The sensors’ block acquires analog signals from the environment, temperature, light level, and acceleration in three dimensions.
The structure of a smartphone is similar, but a smartphone also has a global positioning receiver (GPS) and multiband radio blocks that send and receive continuous-time signals from base stations (antenna sites) of a cellular network.
The GPS receiver acquires signals from multiple satellites to get your latitude and longitude. The primary purpose of the GPS in most smartphones is to provide location information when placing an emergency call (E911).
Four antennas are shown, but only a single multiband antenna is employed in most models, so only a single antenna structure is really needed.
The multiband cellular radio subsystem is thick with signals and systems. The multiband digital communications transmitter (tx) and receiver (rx) allows the smartphone to be backward compatible with older technologies as well as with the newest high-speed wireless data technologies. This transmitter and receiver enable the product to operate throughout the world. A smartphone is overflowing with signals and systems examples!
Cruise control involves both electrical and mechanical signals and systems.
Most new automobiles come equipped with a cruise control system now. This is good news because this feature may keep you from getting a speeding ticket when you’re driving long distances on the interstate. It’s also great for getting better gas mileage. This product also is interesting from a signals and systems standpoint.
The controller is electrical and the plant, the system being controlled, is the car. Wind and hills are disturbance signals, which thwart the normal operation of the control system. The controller puts out a compensating signal to the throttle to overcome wind resistance (an opposing force) and the force of gravity when going up and down hills.
The error signal that follows the summing block is driven to a very small value by the action of the feedback loop. This means that the output velocity tracks the reference velocity. This is exactly what you want.