Modulation and demodulation devices vary the phase and amplitude of a waveform (sometimes referred to as a carrier signal) to encode information or detect variance of a waveform to derive the information signal. Demodulation devices are also referred to as detectors. Modulators and demodulators are either analog or digital. An analog modulator mixes the analog information signal (referred to as the baseband) with an analog carrier for transmission on wired or wireless interfaces. An example of this is FM Radio where audio signals are directly modulated onto an intermediate frequency (IF) and up-converted to a high carrier frequency for transmission. Digital modulation is a similar process, but a digital signal represented by an analog waveform is modulated onto a carrier or number of carriers. Chips that perform analog modulation include devices that can modulate physical characteristics like amplitude modulation (AM), frequency modulation (FM) or even phase modulation (PM). The modulation pattern in the frequency domain can be symmetrical about the carrier frequency or only have one side of the modulation pattern. This is called single or double side-band modulation respectively. Modulation schemes can suppress the actual carrier energy – just transmitting the modulation sidebands (suppressed carrier). This improves the efficiency of transmission. A very important characteristic of such modulation is that levels in the frequency domain must fall within a template provided by the regulations. This is typically band pass or low pass shaped and prevents channels from interfering with each other. Digital modulation schemes use patterns to express combinations of bits called symbols. Symbols are represented as positions mapped in a unit phase plot called a constellation. Quadrature amplitude modulation (QAM) is an example of a digital modulation format that encodes symbols in this way. As signals traverse points on the constellation they trace an eye diagram. Noise and channel shape can introduce jitter and distortion causing receiver errors. This is called opening or closing the eye with errors represented as a bit error rate (BER). Digital modulation employs time domain shaping to compensate for channel characteristics called equalization. Forward error correction (FEC) uses symbol codes with bit redundancy to correct errors in the received signal. Some modulation methods utilize frequency division multiplexing (FDM) to send data simultaneously over several bands for increased bandwidth. Some standards even use pseudo random sequences to encode – for example frequency hopping spread spectrum. Read more Read less