Tektronix P6231 Variable Bias/Offset Active Probe

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Detailed Specifications

Tektronix Catalog Cost
$410 (1989)
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  • Bandwidth : DC to 1.5 GHz
  • Attenuation : 10X
  • Input Resistance : 450 Ω
  • Input Capacitance : 1.6pF
  • Scope Input Resis : 50Ω
  • Compensation Range : ?
  • Readout Pin : Yes
  • Ground Ref : ?
  • ID Button : Yes
  • Max Rated Voltage : 10 VDC


    Designed for amplifiers with an input impedance of 50 ohms, primarily the 11A52 and 11A71.

    The P6231 is an active probe designed for amplifiers with an input impedance of 50 ohms, primarily the 11A52 and 11A71 high-frequency amplifiers. Connection of the P6231 into any other 11000 Series amplifier automatically causes the input impedance to be set at 50 ohms. Up to five volts of bias may be applied to the tip of the P6231 to reduce the DC loading on the circuit under test. The offset voltage is selectable from the mainframe touch screen.

    ECL logic is most commonly operated from a -5.2 V supply with Vcc connected to ground. The output of an ECL gate is the emitter of an NPN emitter follower stage. The output is pulled down to a negative supply (about -2 V) with an external resistor (50 Ω to 100 Ω). Since speed is a major consideration in ECL designs, the interconnections between gates are often transmission lines, and the pull-down resistor doubles as a line termination.

    If a standard 500 Ω, 10X probe without the input Bias/Offset feature were used to examine an ECL output, the probe's 500 Ω resistance to ground would form a voltage divider with the gate's output-termination resistor. This divider can cause distortion of the output signal levels, shift the dc operation point of the output transistor, and reduce the gate's noise margin.

    The dc-load nulling capability of the P6231 helps to solve this problem. By adjusting the Input Bias/Offset Voltage to the ECL low level or to the termination voltage, the only effect of the probe resistance will be a small decrease in the ECL output-termination resistance. The effect of the probe on output voltage levels is negligible.

    Probe power comes through the connector.

    An identify button on the probe allows remote sequencing of Oscilloscope programs.

    (excerpt from the 1989 Tektronix catalog)
    Attenuation :10X
    Input Resistance :450 Ω
    Input Capacitance :1.6 pF
    Bandwidth (-3 dB) :DC to 1.5 GHz
    Maximum Input Voltage :10 VDC

    (excerpt from 1989 Tektronix catalog)

    Tektronix Catalog CostLow BidHigh Bidaverage
    $410 (1989) ...
    $46.00 4/1/03 #2518784525 8t0888 (used) (5 bids $20 start)