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.

Tektronix 282
Unity gain buffer
Tektronix Type 282

Produced from 1966 to (?)

Manuals
(All manuals in PDF format unless noted otherwise)

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.

Power Supply

The 282 internally is supplied with ±10 V stabilized with Zener diodes. This allows the 282 to be compatible with the different negative supply voltages being present on the B pin of the probe power connector ranging from -12.2 V (3S1) to -25 V (4S1). Positive supply is from +100 V.

Compatible probe power sampling plug ins

The 282 MOD 125D (015-0146-00) is a modified version which is supplied by a 015-0073-00 ±12 V power supply. Using a 015-0147-00 tee connector, two 282 MOD 125D units may be supplied.

Pictures