Load-pull is the colloquial term applied to the process of systematically varying the
impedance presented to a device under test (DUT), most often a
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
, to assess its performance and the associated conditions to deliver that performance in a network.
While load-pull itself implies impedance variation at the load port, impedance can also be varied at any of the ports of the DUT, most often at the source.
Load-pull is required when
superposition is no longer applicable, which occurs under large-signal operating conditions that make linear approximations unusable. The term load-pull derives from classical oscillator characterization whereupon variation of the
load impedance The input impedance of an electrical network is the measure of the opposition to current ( impedance), both static ( resistance) and dynamic ( reactance), into the load network that is ''external'' to the electrical source. The input admittance (the ...
pulls the oscillation center frequency away from nominal. Source-pull is also used for noise characterization, which, although linear, requires multiple impedances to be presented at the source to enable simultaneous solution of an
over-determined system
In mathematics, a system of equations is considered overdetermined if there are more equations than unknowns. An overdetermined system is almost always inconsistent (it has no solution) when constructed with random coefficients. However, an ov ...
that yields the four noise parameters.
Load-pull is the most common method globally for RF and MW
power amplifier
An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspea ...
(PA) design, transistor characterization,
semiconductor
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
process development, and ruggedness analysis. A central theme of load-pull is management of
nonlinearity
In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...
versus analysis of nonlinearity, the latter being the domain of advanced mathematics that often yields little physical insight to nonlinear phenomena and suffers from an inability to accurately render actual behavior embedded in a network with significant parasitic and distributed effects. With automated load-pull, it is possible to fully optimize and design a final stage for GSM applications in less than a day, thereby providing a dramatic reduction in design cycle-time while assuring the best possible performance trade-off has been achieved.
While there are in theory no physical limits on the frequency of which load-pull can be performed, most load-pull systems are based on passive distributed networks using either the slab transmission line in its TEM mode or the rectangular
waveguide
A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...
in its TE01 mode. Lumped tuners can be made for HF and VHF frequencies, whereas active load-pull is ideal for on-wafer mm-wave environments, where substantial loss between the tuner and DUT reference-plane limits maximum VSWR.
See also
*
Impedance matching
In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize signal ...
*
Electronic test equipment
Electronic test equipment is used to create signals and capture responses from electronic devices under test (DUTs). In this way, the proper operation of the DUT can be proven or faults in the device can be traced. Use of electronic test equipmen ...
**
Transistor tester
Transistor testers are instruments for testing the electrical behavior of transistors and solid-state diodes.
Types of tester
There are three types of transistor testers each performing a unique operation.
* Quick-check in-circuit checker
* Serv ...
References
External links
Radio electronics
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