The Illustrated Dictionary of Electronics - Loscha

160 current saturation • cutoff frequencycurrent saturation In the operation of a device(such as a transistor, saturable reactor, or magneticamplifier), the leveling off of current at avalue beyond which no further increase occurs—even though an input parameter is further increased.current sense amplifier An amplifier used to increasethe sensitivity of, or to decrease the loadingof, a current-sensing component.current sensing Sampling a current (e.g., whenthe voltage drop across a series resistor is used asa proportional indication of the current flowingthrough the resistor).current-sensing resistor A low-value resistor insertedinto a circuit primarily for current sensing.current sensitivity In a current meter or galvanometer,current (in amperes or fractionsthereof) per scale division.current-sheet inductance Symbol, L S . The lowfrequencyinductance of a single-layer coil, calculatedwith the formula L S = (0.10028 a 2 N 2 )/s,where L S is in microhenrys, a is the coil radius ininches, N is the total number of turns, and s isthe coil length in inches.current shunt 1. A resistor connected in parallelwith a voltmeter to convert it into an ammeter. 2.A resistor connected in parallel with the input ofa voltage amplifier to make the response of theamplifier proportional to input-signal current.current sink A circuit or device through which aconstant current can be maintained.current-sinking logic A form of bipolar digitallogic. Current flows from one stage to the input ofthe stage immediately before.current-squared meter An ammeter or milliammeterwhose deflection is proportional to thesquare of the current.current-stability factor In a common-base connectedbipolar transistor, the ratio dI E /dI C , whereI E is the emitter current and I C is the collectorcurrent.current strength The magnitude of electric current(see CURRENT) (i.e., the number of carriersflowing past a given point per unit time, expressedin coulombs per second or in amperes).current transformer 1. A transformer used to increaseor decrease current flow. A primary-tosecondarystep-up turns ratio reduces thecurrent; a primary-to-secondary step-down turnsratio increases the current. 2. A particular transformer(as in 1) used to change the range of an alternating-currentmilliammeter or ammeter.current vector In a vector diagram, a line with anarrowhead (vector) showing the magnitude andphase of a current. Compare VOLTAGE VEC-TOR.current-voltage feedback In an amplifier or oscillator,the process of applying some of the outputcurrent and voltage to the input. This feedbackmight be in phase (positive) or out of phase (negative),with respect to the input.cursor 1. A marker that indicates the positionwhere a character can be entered in a video alphanumericdisplay. Commonly used in computersand word processors. 2. The sweeping line ona radar display. 3. The movable marker on a sliderule.curve trace 1. A device that supplies a specialvariable test voltage to a component or circuit undertest, at the same time supplying a sweep voltageto an oscilloscope. The component’s outputvoltage is also presented to the oscilloscope. As aresult, the response curve of the component appearson the oscilloscope screen. 2. A device thatproduces a permanent record (photographic orgraphic) of an electrical phenomenon. Also calledOSCILLOGRAPH or RECORDER.curvilinear trace A trace made on paper withcurved vertical lines. The lines are curved tomatch the arc through which the recording penswings.cut-in angle In a semiconductor rectifier circuit, aphase angle slightly greater than zero degrees, atwhich current conduction begins. Compare CUT-OUT ANGLE.Cutler antenna A parabolic-dish antenna, inwhich the driven element consists of a waveguidethat has two apertures on opposite sides ofa resonant cavity.Cutler feed An aircraft antenna feed system inwhich radio-frequency (RF) energy is fed to the reflectorby a resonant cavity at the end of a waveguide.Cutler tone control A dual resistance-capacitance(RC) filter circuit of the general bridged-tee variety.Variation of the series leg provides adjustabletreble boost; variation of the shunt leg providesadjustable bass boost.cutoff 1. The process of reducing some operatingparameter, such as collector current, to zero byadjusting the bias at the input electrode. 2. Thepoint on the characteristic curve of an amplifyingdevice, at which the output current drops to zerounder no-signal conditions. 3. The lowestfrequency at which a waveguide will efficientlyfunction. 4. The frequency or frequencies correspondingto the point or points in a filterresponse, at which the attenuation is threedecibels greater than the lowest attenuation withinthe passband. See also CUTOFF FREQUENCY.cutoff attenuator A variable, nondissipating attenuatorconsisting of a variable length of waveguideused at a frequency below cutoff.cutoff bias In a transistor or vacuum-tube circuit,the value of control-electrode bias that producesoutput current cutoff.cutoff current Symbol, I co . In a transistor, thesmall collector current that flows when the emittercurrent is zero (common-base circuit) or whenthe base current is zero (common-emitter circuit).cutoff frequency 1. Symbol, f co . The high frequencyat which the current-amplification factor