Read the text. Find the sentences with the Complex Object and the Complex Subject.
Analogue and digital displays
You have only to think of the array of instruments in the cockpit of a modern airliner, or the control room of a power station to realize that the most convenient way to convey information to a human operator of an electronic system is to use some form of visual display. We know two types of displays to be used, analogue or digital, but sometimes a combination of both of them. An analogue multimeter displays the value of a measurement on a moving-coil meter that uses a pointer moving over a calibrated scale. On the other hand, a digital multimeter generally uses a liquid crystal display (LCD) or a seven-segment light-emitting diode (LED) display to give a numerical value of a measurement.
Digital displays based on LCDs and LEDs are known to have largely replaced analogue displays in many different types of instrument. The main advantage of LED and LCD displays is that, they are more rugged and can stand up to vibration better than the rather fragile moving-coil meter. They are also cheaper and easier to manufacture, and purpose-designed integrated circuits are readily available to operate them. But perhaps the main reason for their rise to fame is that many of today′s electronic systems process digital signals that are compatible with the operating principles of LCDs and LEDs.
Numerical display is not always the preferred choice in a digital system. Sometimes it is better to use an analogue display when the change in a reading is looked for. Analogue displays are often used on hi-fi amplifiers in preference to digital displays to indicate the audio power delivered to loudspeakers or the signal strength of a radio station. These analogue displays use a “bar of light” made of discrete LEDs or LCD segments that lengthen or shortens in response to the signal strength. Analogue displays of that kind make it easier to see how the signal strength changes with time rather than having to interpret the precise value. Perhaps that is why some people prefer digital watches with LCD “hands” since the time of day seems to have more meaning when set against the twelve-hour scale of time round the face of the watch.
The combination of electronics and optics is known to be optoelectronics. For example, an LED is an optoelectronics device. Numbers, letters and other symbols are formed by the selective illumination of one or more segments arranged in the form of the figure “8”. Each of the LEDs labeled ‘a’ to ‘g’ can be switched on or off by digital circuits. A display of this type, forming both numbers and some letters, is known as an alphanumeric display.
The LCD is a popular method of displaying information, especially in digital watches and pocket games. LCDs can display not just numerical data, but also words and pictures. Large-area LCDs rather than a cathode-ray tube are commonly used on some oscilloscopes, laptop computers and scientific calculators. The main reason for choosing LCDs for these applications is that their power consumption is minute compared with LED displays. Whereas the LED display requires electrical power to generate light, the LCD simply controls available light. This means that it is easily seen in bright sunlight but it cannot be seen in the dark unless the display is “backlighted”.
The LCD relies on the transmission or absorption of light by certain organic carbon crystals that behave as if they were both solid and liquid, that is, their molecules readily take up a pattern as in a crystal and yet flow as a liquid. In the construction of the common LCD unit, this compound is sandwiched between two closely-spaced, transparent metal electrodes that are in the form of a pattern, e.g. as a seven-segment digit. When an a.c. signal is applied across a selected segment, the electric field causes the molecular arrangement of the crystal to change, and the segment shows up as a dark area against a silvery background. A polarizing filter on the top and bottom of the display enhances the contrast of black against silver by reducing reflected light. This type of LCD is called a field-effect LCD, since it relies on the electric field produced by the a.c. signal.
