Glossary of Control Component Terms

A control component specification is written in a dialect. Most of its words come from measurement practice rather than from a dictionary, and almost none of them are defined on the page that uses them. What follows is that dialect, in alphabetical order, with the misreading each term usually produces. Quantities, units and measurements are in the datasheet parameter index; this page is about the words.

The terms

Absorptive switch

A switch whose blocked port is terminated inside the housing, so that power sent into it is dissipated rather than reflected back toward the source. Usual confusion: It is read as a quality grade. It is a topology choice, and it usually costs something in insertion loss and complexity.

Bias

The direct current condition applied to a semiconductor to place it in a chosen state. Forward bias makes a PIN diode conduct; reverse bias makes it block. Usual confusion: It is confused with the control logic level. The logic level commands a driver; the driver produces the bias.

Control line

The conductor that carries the command to the part, separate from the signal path. Usual confusion: It is treated as an accessory. On an assembly it is part of the specification.

DLVA

Detector log video amplifier: a detector and a logarithmic video amplifier specified together, from radio frequency input to video output. Usual confusion: It is read as a detector with a gain block. The point is that the whole transfer is specified end to end.

Dynamic range

The span of input power over which a detector keeps its logging error inside a stated limit. Usual confusion: It is quoted without the error limit, which makes it meaningless. The limit is the specification.

Flatness

The variation of a quantity across the specified frequency band at a fixed setting. Usual confusion: It is used interchangeably with accuracy. Flatness varies with frequency; accuracy varies with setting.

Hot switching

Changing the state of a switch while radio frequency power is present at its ports. Usual confusion: It is assumed to be allowed. It is a stated condition, and not every part is specified for it.

Insertion loss

The loss a component introduces into the path it is inserted in, measured through the state that conducts. Usual confusion: It is compared between parts measured over different bands, which is not a comparison.

Intercept

The reference point of the ideal straight line fitted to a logarithmic detector transfer. Usual confusion: It is read as an output offset. It is a property of the fitted line, not of the hardware alone.

Isolation

The attenuation between two ports through the state that blocks. Usual confusion: It is read as a guarantee that nothing arrives. It is a ratio, and a large enough input still produces an output.

Logging error

The departure of a real logarithmic transfer from the ideal straight line, expressed on the input scale. Usual confusion: It is confused with linearity of the video output. It is measured against a logarithmic ideal, not a linear one.

Monotonic

A stepped attenuator is monotonic when its attenuation never decreases as the control word increases. Usual confusion: It is assumed to follow from accuracy. A part inside its accuracy limit can still reverse, and a control loop will fail on it.

PIN diode

A diode with an intrinsic layer between its doped regions. Above its transit frequency it behaves as a current controlled resistor rather than a rectifier. Usual confusion: It is thought of as a fast rectifier. The stored charge in the intrinsic layer is exactly what makes it useful as a switch.

Reflective switch

A switch whose blocked port presents a large mismatch, so that power sent into it returns toward the source. Usual confusion: It is read as a defect. It is often the simpler, lower loss choice when nothing upstream objects to the reflection.

Reference plane

The point in a measurement setup to which a calibration refers, and therefore the point a result describes. Usual confusion: It is assumed to be at the device. It is where the calibration standards were connected.

Return loss

The ratio, in decibels, between an incident wave and the wave reflected back from a port. Usual confusion: A larger number is better here, which is the opposite of insertion loss, and tables get sorted the wrong way round.

Screening

A sequence of tests applied to every unit, as opposed to qualification testing applied to samples. Usual confusion: A method number is read as a promise about service life. It certifies that the described test was passed under the described conditions.

Slope

The gradient of the ideal logarithmic transfer of a detector, expressed in millivolts per decibel. Usual confusion: It is read as an accuracy figure. Slope describes the ideal line; logging error describes the distance from it.

SPnT

Single pole, n throw: one common port routed to one of n others. SPST and SPDT are the cases where n is one and two. Usual confusion: The port count is read as the only difference. Isolation between the unselected ports usually changes with it.

Tangential signal sensitivity

The input level at which the top of the noise without a signal and the bottom of the noise with one become tangent on a display. Usual confusion: It is read as an absolute floor. It is a visual criterion that depends on the observer and on the video bandwidth.

Video bandwidth

The bandwidth of the detected output, which fixes the shortest pulse the output can reproduce. Usual confusion: It is maximised on its own. Widening it admits more noise and moves sensitivity the wrong way.

VSWR

Voltage standing wave ratio: the same reflection that return loss describes, expressed as a ratio rather than in decibels. Usual confusion: Two specifications are compared across the two scales without converting, which reverses the conclusion.

The measurement side of all of this is in the measurement section, and the quantities themselves, with their units, are in the datasheet parameter index.