282

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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 withan 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 V_gs = 0, maintaining a constant (I_dss) 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

• 1S1
• 3S1
• 3S76
• 4S1
• 4S2

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

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  282 MOD 125D in 1970 catalog

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