View source for P6230

{{Probe Sidebar
|manufacturer=Tektronix
|model=P6230
|summary=1.5 GHz, 450:50 Ω passive probe
|image=P6230-6.jpg
|caption=Tektronix P6230
|for=50 Ω scope inputs
|introduced=1984
|discontinued=(?)
|manuals=
* [[Media:070-4211-00.pdf|P6230 Operator manual]] (OCR)
* [[Media:070-6027-00.pdf|P6231 Instruction manual]] (OCR)
}}
[[File:P6230-1.jpg|thumb|right|250px|P6230 termination box]]
The '''Tektronix P6230''' and '''P6231''' are passive ×10 (450:50 Ω) probes with 1.5 GHz bandwidth and DC offset capability, intended to minimize DC probe-loading effect when used on logic circuits.

The '''P6230''' has an offset control potentiometer in the termination box and connects to the scope, e.g. [[7000 series scopes]], through a [[BNC connector]] with ×10 readout pin.  It can be powered from 7000 series mainframes having [[LEMO S-series connector]]s for probe power, or compatible units such as the [[1101]].

The '''P6231''' is a TekProbe Level 2 probe intended for 11000 series plugins such as the [[11A32]] or [[11A71]].  Offset control and power are provided by the scope mainframe through a [[Tekprobe BNC connector]].

The P6230/6231 shares accessories with many other Tektronix [[subminiature modular probes]] although the input hybrid is unique.  Tip color is yellow, connector end color is blue, part number [[206-0279-00]].  Its end to end resistance is 400 Ω.

{{BeginSpecs}}
{{Spec | Bandwidth       | DC to ≥ 1.5 GHz }}
{{Spec | Rise time       | ≤ 230 ps        }}
{{Spec | Attenuation     | 10×             }}
{{Spec | Input Impedance | 450 Ω // 1.3 pF  (1.6 pF guaranteed) }}
{{Spec | Signal delay    | 8.7 ± 0.1 ns    }}
{{Spec | DC offset       | −5 V ≤ (V<sub>signal</sub> + V<sub>offset</sub>) ≤ +5 V }}
{{Spec | Features | 
* Readout Pin 
* Switchable 50 Ω termination
}}
{{EndSpecs}}

==Internals==
The P6230/6231 probes are sometimes described as FET probes or active probes, however, as the circuit diagram clearly shows, this is not correct.  After the 400 Ω input hybrid, the AC component of the input signal is connected directly to the scope input through a 1 μF capacitor, then terminated in 50 Ω either in the scope input or the switchable terminator.  The active circuit in the P623x, a standard NE5532 dual opamp, has the function of restoring and offsetting the input signal's low-frequency and DC components. This approach is similar to the feed-beside technique used in the [[7104]] scope and [[7A29]] amplifier.  

Tek explains the raison d'être for the P6230/P6231 thus:
<blockquote>
The P6230 acts as a standard 500 Ω passive voltage probe with the additional capability of having an adjustable tip "nulling voltage." This feature reduces the dc-loading effects on the probe when it is used to measure signals whose mid-voltage value is other than zero volts, or in circuits where the termination impedance is returned to other than ground level. The Input Bias/Offset Voltage may be adjusted so that at a particular test-signal voltage both ends of the probe input-resistor are at equal potentials and no current is flowing through the resistor. 

ECL logic is most commonly operated from a −5.2 V supply with V<sub>CC</sub> 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, 10× 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 P6230 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. 
</blockquote>

==Links==
* [http://www.barrytech.com/tektronix/probes/tekp6230.html P6230] / [http://www.barrytech.com/tektronix/probes/tekp6230.html P6231] @ barrytech.com (incorrectly described as active probe)

==Prices==
{| class="wikitable"
|-
! Year
!   1984  
!   1987  
!   1989  
!   1991  
!   1995  
|-
! P6230 Catalog price
|align=right|  $385
|align=right|  $395
|align=right|  $420
|align=right|  $525
|align=right|  –
|-
! In 2023 Dollars
|align=right|  $1,100
|align=right|  $1,100
|align=right|  $1,000
|align=right|  $1,200
|align=right|  –
|-
! P6231 Catalog price
|align=right|  –
|align=right|  $410
|align=right|  $410
|align=right|  $525
|align=right|  $799
|-
! In 2023 Dollars
|align=right|  –
|align=right|  $1,200
|align=right|  $1,000
|align=right|  $1,200
|align=right|  $1,600
|}
 
==Pictures==

<gallery>
P6230-1.jpg | P6230 compensation box
P6230-2.jpg | P6230 Switchable terminator
P6230-4.jpg | P6230 Compensation box interior
P6230-5.jpg | P6230 Compensation box interior
Tek p6231.jpg | P6231
P6230-6.jpg | P6230 probe tip with alligator clip ground lead
206-0279-00.jpg | [[206-0279-00|Input hybrid]]
P6230-3.jpg | Probe tip components
P6230-7.jpg | Low-inductance ground lead
P6230-8.jpg 
P6230-9.jpg 
P6230-10.jpg | Probe-to-PCB adapters
P6230-11.jpg | Probe-to-PCB adapters
P6230-circuit.jpg    | P6230 circuit diagram
P6230-impedance.jpg  | P6230 input impedance graph
</gallery>

===Measurements===
<gallery>
P6230-rt1.jpg | P6230 Rise time measured on a [[7S12]] with [[S-52]] and [[S-4]] heads, P6230 ground sleeve connected directly at S-52 output (no ground lead)
P6230-rt2.jpg | P6230 Rise time without ground lead: 9.2 * 20 ps = 184 ps (equiv. to 1.9 GHz bandwidth)
P6230-rt3.jpg | Effect of using the "low inductance" ground lead - rise time 400 ps, bandwidth 875 MHz
P6230-rt4.jpg | Using the 250 mm (9.8") alligator ground lead - severe pulse distortion, rise time ~3 ns (115 MHz)!
P6230-bw.jpg  | Bandwidth vs. grounding, from manual
</gallery>


[[Category:Subminiature modular probes]]
[[Category:50 Ω Oscilloscope probes]]