low-signal impedance
121Track circuit — A track circuit is a simple electrical device used to detect the presence or absence of a train on rail tracks, used to inform signallers and control relevant signals. Principles and operation The basic principle behind the track circuit lies in… …
122Switching amplifier — A switching amplifier or class D amplifier is an electronic amplifier which, in contrast to the active resistance used in linear mode AB class amplifiers, uses switching mode of transistor to regulate power delivery. The amplifier, therefore,… …
123Electrical characteristics of dynamic loudspeakers — A dynamic loudspeaker driver s chief electrical characteristic is its electrical impedance versus frequency. Explanation The most common driver type is an electro mechanical transducer using a voice coil rigidly connected to a diaphragm… …
124Piezoelectric accelerometer — A piezoelectric accelerometer that utilizes the piezoelectric effect of certain materials to measure dynamic changes in mechanical variables. (e.g. acceleration, vibration, and mechanical shock) As with all transducers, piezoelectric… …
125Metal-mesh optical filters — are optical filters made from stacks of metal meshes and dielectric. They are used as part of an optical path to filter the incoming light to allow frequencies of interest to pass while reflecting other frequencies of light. Metal mesh filters… …
126Positive feedback — Alarm or panic can spread by positive feedback among a herd of animals to cause a stampede. Positive feedback is energy taken from the output of a system and reapplied to the input, which is phase congruent with the input signal. A system… …
127Copper wire and cable — Copper has been used in electric wiring since the invention of the electromagnet and the telegraph in the 1820s.[1][2] The invention of the telephone in 1876 proved to be another early boon for copper wire.[3] Today, despite competition from… …
128Common source — Figure 1: Basic N channel JFET common source circuit (neglecting biasing details). Figure 2: Basic N channel JFET common source circuit with source degeneration …
