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The Tektronix Type 282 is an active adapter [[introduced in 1966]] that allows high-impedance | The '''Tektronix Type 282''' is an active adapter [[introduced in 1966]] that allows high-impedance | ||
probes to be used with instruments that have | probes to be used with instruments that have 50 Ω inputs. It is a unity-gain buffer with | ||
an input impedance of | 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 | 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 | and transistor B operates as a current source biased with V<sub>gs</sub> = 0, maintaining a constant (I<sub>dss</sub>) current through transistor A, independent of input signal voltage. After the FET input stage, | ||
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 | 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 | 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 | greater than unity, which allows the overall gain of the 282 to be trimmed for exactly unity | ||
gain. The | gain. The rise time is 3 ns when driven from a 25 Ω source. | ||
==Manual== | |||
* [http://w140.com/tek_282.pdf Tektronix 282 Manual (PDF)] | * [http://w140.com/tek_282.pdf Tektronix 282 Manual (PDF)] | ||
==Pictures== | |||
<gallery> | <gallery> | ||
Image:Tek 282.jpg | Image:Tek 282.jpg | ||
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[[Category:Oscilloscope Probe Accessories]] | [[Category:Oscilloscope Probe Accessories]] | ||
[[Category:Introduced in 1966]] | |||
Revision as of 03:29, 19 August 2014
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.
