QAM, or Quadrature Amplitude Modulation, is a type of modulation scheme. In QAM, data is conveyed by changing the amplitude of two carrier waves through modulation.
The two carrier waves involved in QAM are normally sinusoids, functions that describe a wavelike quality of time. The QAM carrier waves are out of phase with each other by around 90 degrees, hence the name.
The structure of QAM can be seen in a setting that includes a transmitter and a receiver. The QAM transmitter first splits into two parts the flow of bits it will transmit. These parts should always be equal to ensure that two independent signals would be transmitted. Through this process, a 90-degree phase is created between the two channels.
The receiver then accepts the signals sent by the transmitter. Once it takes in the signals, the receiver carries out an inverse version of the transmitter’s process. There is, however, a phase delay occurring between the transmitter and the receiver. This is compensated for by the receiver’s synchronization.
QAM has a number of forms:
- Analog QAM, for instance, is used in PAL and NTSC television systems;
- Compatible QAM is used in AM stereo radio. In this system, Compatible QAM is used to carry information regarding the stereo difference;
- Quantized QAM is used in certain hardware devices such as cable modems and digital cable television.
DLP stands for Digital Light Processing. It is a type of digital display technology developed by Texas Instruments, Inc. DLP consists of procedures where video images are projected using a specialized light source. Usually this light source is a powerful lamp. The light produced by the source is reflected off thousands of microscopic mirrors formed on a chip. Each of the microscopic mirrors corresponds to a single pixel.
The microscopic mirrors used in DLP are set to perform specific functions. They reflect light toward the DLP lens to produce the color white. In contrast, the mirrors reflect light away from the DLP lens to produce black. Between the two said points, the mirrors modulate to produce various shades of gray. Intricate motors are used in tilting the mirrors more than a thousand times per second to a specific angle. This process will produce images as crisp and as accurate as possible.
In addition, three-chip versions are used in the DLP technology to produce the colors red, green, and blue. Once the signals have passed through the lens, they are then sent to a screen. Such equipment involved in the process are called Digital Micromirror Devices (DMD’s)
DLP is used in various applications and pieces of hardware. Most commercial projectors use the DLP technology. This enables them to provide compact, high-resolution digital displays. High Definition TVs or HDTVs are other good examples of hardware that use DLP. The wide-screen TVs and video displays used by certain theaters were made using the DLP technology.