If you get the "Sorry, the file cannot be displayed. There seems to be a technical issue ..." error when trying to view an image, please make sure you access the site at http://w140.com/tekwiki/, not www.w140.com/tekwiki/ (with "www"). Sorry for the inconvenience - we are looking for a generic solution.


From TekWiki
Jump to: navigation, search

The Tektronix Type 282 is an active adapter introduced in 1966 that allows high-impedance probes to be used with instruments that have 50 Ω inputs. It is a unity-gain buffer with an input impedance of 1 MΩ in parallel with 16.5 pF and a low output impedance.

The high-impedance input stage is a dual-JFET where transistor A operates as a source-follower and transistor B operates as a current source biased with Vgs = 0, maintaining a constant (Idss) current through transistor A, independent of input signal voltage. After the FET input stage, the signal is fed to a Sziklai pair formed of a PNP transistor first, driving an NPN output transistor. The Sziklai pair is non-inverting and has a voltage gain greater than unity, which allows the overall gain of the 282 to be trimmed for exactly unity gain. The rise time is 3 ns when driven from a 25 Ω source.

This active adapter is powered over 1S1, 3S1 and 3S76.