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{{Plugin Sidebar | {{Plugin Sidebar | ||
|manufacturer=Tektronix | |||
summary=250 MHz FET-probe amplifier | | |type=7A11 | ||
image=tek-7a11-front.jpg | | |summary=250 MHz FET-probe amplifier | ||
caption=7A11 front view | | |image=tek-7a11-front.jpg | ||
introduced=1969 | | |caption=7A11 front view | ||
discontinued=1984 | | |introduced=1969 | ||
series= | |discontinued=1984 | ||
manuals= | |series=7000-series scopes | ||
* [[Media:070-0984-00.pdf|Tektronix 7A11 Manual]] | |designers=John Addis;Ron Peltola;Glenn Bateman | ||
|manuals= | |||
* [[Media:070-0984-00.pdf|Tektronix 7A11 Manual]]<br /><small>[[Media:070-0984-00 (2).pdf|Alternate copy]] (OCR)</small> | |||
}} | }} | ||
The '''Tektronix 7A11''', [[introduced in 1969]], is a vertical plug-in for [[7000-series scopes]]. | The '''Tektronix 7A11''', [[introduced in 1969]], is a vertical plug-in for [[7000-series scopes]]. | ||
It includes a permanently attached FET probe. The bandwidth of a 7A11 in a [[7904]] is 250 MHz. | It includes a permanently attached FET probe. The bandwidth of a 7A11 in a [[7904]] is 250 MHz. | ||
The front-end FET is a [[151-1034-00]]. | |||
The 7A11 contains a selectable three-pole 20 MHz bandwidth limit filter. | |||
{{BeginSpecs}} | {{BeginSpecs}} | ||
{{Spec | Bandwidth | 250 MHz (in [[7904]]) }} | {{Spec | Bandwidth | 250 MHz (in [[7904]]) }} | ||
{{Spec | Deflection | 5 mV/Div to 20 V/Div | {{Spec | Deflection | 5 mV/Div to 20 V/Div, 1–2–5 }} | ||
{{Spec | Input resistance | 1 MΩ }} | {{Spec | Input resistance | 1 MΩ }} | ||
{{Spec | Input capacitance | | {{Spec | Input capacitance | | ||
* 5 mV/Div to 50 mV/Div | * 5.8 pF @ 5 mV/Div to 50 mV/Div | ||
* 3.4 pF @ 100 mV/Div to 1 V/Div | |||
* 2.0 pF @ 2 V/Div to 20 V/Div | |||
* Add 1.2 pF for BNC input adapter | * Add 1.2 pF for BNC input adapter | ||
* Add 1.2 pF for AC coupling plug-on capacitor | * Add 1.2 pF for AC coupling plug-on capacitor | ||
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}} | }} | ||
{{EndSpecs}} | {{EndSpecs}} | ||
==Links== | |||
{{Documents|Link=7A11}} | |||
==Internals== | ==Internals== | ||
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Regarding the 7A11, its designer [[John Addis]] says: | Regarding the 7A11, its designer [[John Addis]] says: | ||
<blockquote> | <blockquote> | ||
The 7A11 input capacitance is 5.8 pF from 5 mV/Div to 50 mV/Div, goes down to 3.4 pF from | The 7A11 input capacitance is 5.8 pF from 5 mV/Div to 50 mV/Div, goes down to 3.4 pF from 100 mV/Div to 1 V/Div, and down again to 2.0 pF from 2 V/Div to 20 V/Div. | ||
100 mV/Div to 1 V/Div, and down again to 2.0 pF from 2 V/Div to 20 V/Div. Because the AC | Because the AC coupling is attained with a plug-on capacitor (that adds 1.2 pF to the input C), a DC offset is supplied to reduce the need for AC coupling. | ||
coupling is attained with a plug-on capacitor (that adds 1.2 pF to the input C), a DC offset | |||
is supplied to reduce the need for AC coupling. | A nice thing about the 7A11 was that the probe cable length was adjustable in six steps to just over 7 feet in length. | ||
You just uncoil however much cable length you want. | |||
A nice thing about the 7A11 was that the probe cable length was adjustable in six steps | The 7A11 was admittedly clumsy to use because of the probe size. It had some trouble — DC drift, RF pickup at 5 mV, 100 mV and 2 V/Div. | ||
to just over 7 feet in length. You just uncoil however much cable length you want. | It was not very popular partially because it was expensive, $850 for single channel vs. dual channel [[7A12]] (105 MHz) at $700. | ||
But there was never another 1 MΩ 7000-series plugin as fast as the 7A11 ... and it was one of the originals! | |||
The 7A11 was admittedly clumsy to use because of the probe size. It had some trouble — | |||
DC drift, RF pickup at 5 mV, 100 mV and 2 V/Div. It was not very popular partially | |||
because it was expensive, $850 for single channel vs. dual channel [[7A12]] (105 MHz) at $700. | |||
But there was never another 1 MΩ 7000-series plugin as fast as the 7A11 ... and it was | |||
one of the originals! | |||
The [[7A16]] (single channel plugin) was also 150 MHz, but that was a year later. | The [[7A16]] (single channel plugin) was also 150 MHz, but that was a year later. | ||
Then the [[7904]] came out in late 1971. That made the 7A11 a 250 MHz plugin (for $950). | Then the [[7904]] came out in late 1971. That made the 7A11 a 250 MHz plugin (for $950). | ||
The [[7A16]] was then 225 MHz (for $625). The 7A16 disappeared rapidly and became the [[7A16A]], | The [[7A16]] was then 225 MHz (for $625). The 7A16 disappeared rapidly and became the [[7A16A]], still 225 MHz in 1973. | ||
still 225 MHz in 1973. | |||
In 1972, the [[485]] came out with a 250 MHz, 1 MΩ input. | In 1972, the [[485]] came out with a 250 MHz, 1 MΩ input. | ||
The 485 used a faster IC process | The 485 used a faster IC process ("[[SH2]]", 3.5 GHz) but the 1 MΩ to 50 Ω converter used only discrete devices. (See Electronics June, 1972.) | ||
("[[SH2]]", 3.5 GHz) but the 1 MΩ to 50 Ω converter used only discrete devices. | |||
(See Electronics June, 1972.) | By 1974, the 7A11 cost $950 and the new, popular [[7A26]] (dual trace) was $1,050, not counting probes. | ||
But that would still only get you to 50 mV/div with a (9.5 pF, 3 foot, × 10) probe, five years after the 7A11 introduction. | |||
[[Tom Rousseau]] designed the 7A26 which used the faster IC process and a [[155-0078-00|vertical IC I designed for the 485]]. | |||
By 1974, the 7A11 cost $950 and the new, popular [[7A26]] (dual trace) was $1,050, not | The 7A26 sold so well that Tektronix presented Tom with an entirely gold plated 7A26! | ||
counting probes. But that would still only get you to 50 mV/div with a (9.5 pF, 3 foot, × 10) | Obviously, he still has it. | ||
probe, five years after the 7A11 introduction. | |||
faster IC process and a [[155-0078-00|vertical IC I designed for the 485]]. The 7A26 sold so well that | Remember also that the 7A11 was introduced at the same show as the HP183A/1830A/1840A, faster (250 MHz), smaller, lighter, and less expensive with better triggering than 7000 series had. | ||
Tektronix presented Tom with an entirely gold plated 7A26! Obviously, he still has it. | |||
Remember also that the 7A11 was introduced at the same show as the HP183A/1830A/1840A, | |||
faster (250 MHz), smaller, lighter, and less expensive with better triggering than 7000 series had. | |||
Their secrets were Al DeVilbiss and a faster IC process. We had neither. | Their secrets were Al DeVilbiss and a faster IC process. We had neither. | ||
The star-crossed [[7A12]], which was supposed to be the dual trace flagship of the original plugins, was only 105 MHz, not the hoped-for 150 MHz. | |||
That was partially due to the fact that it used the existing Tek IC process (about 1 GHz). The HP IC process was about 3 GHz. | |||
The 7A11 used discrete NPN and PNP transistors with 4 GHz f<sub>t</sub>. | |||
There is one noteworthy point I would like to make about the 7A11. In those days, the different V/div settings were generally attained using fixed high impedance attenuators, usually stacked one after another and few with more than ×10 attenuation. | |||
I wanted the 7A11 to be able to handle the full useful range of sensitivites that other plugins attained when adding a ×10 probe ... that meant going to 20 V/Div. | |||
But you could certainly get to 5 mV/Div, which you could not attain with a 5 mV/Div plugin and a ×10 passive probe. | |||
But using that scheme, if the 7A11 went to 20 V/Div, it would have to stack three ×10 attenuators inside the probe, making it a behemoth, and even if you did, that would still leave the ×2 and ×5 attenuations up to gain switching in the amplifier. | |||
Problem with gain switching is, the bandwidth and transient response tend to change when you change amplifier gain. | |||
The greater the gain change, the greater the bandwidth/transient response change in the amplifier. | |||
The more gain settings you had, the worse it got due to longer leads and more parasitics. | |||
To get a 1-2-5 sequence from 5 mV/Div to 20 V/Div, it had the worst of all possible worlds. | |||
The 7A11 needed two ×20 attenuators in the probe and that meant that it needed not just ×1, ×2 and ×5 gains in the amplifier, but ×1, ×2, ×2.5, ×4, ×5 and ×10! | |||
This had not been done before, but the 7A11 does it without any change in transient response! | |||
The secret is three entirely passive, [[miniature relays | relay-switched]], O-pad attenuators: ×2, ×2, and ×2.5 in a balanced transmission line environment. | |||
Stack them up (as you can do with matched pads) and you get all the combinations you need: ×1, ×2, ×2.5, ×4, ×5, and ×10. From 5 mV/Div to 20 V/Div, twelve different V/div settings, more than any other high speed plug in! | |||
I got a patent on the variable attenuator, which was just a JFET shunting the O-pads. | |||
The patent had to do with making the gain vs. control rotation linear, which does not simply happen with linear gate-source voltage control. | |||
The JFET causes a small change in transient response, but not a bad one. | |||
[[Ron Peltola]] (of [[Peltola connector]] fame) designed the probe. I helped on the probe's amplifier. | |||
</blockquote> | </blockquote> | ||
The | The group that did the probe design was [[Ken Holland]]'s High Frequency Component Design Group. | ||
Ron Peltola was the engineer. | |||
==Links== | ==Links== | ||
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|align=right| $2,700 | |align=right| $2,700 | ||
|- | |- | ||
! | ! 2023 value | ||
|align=right| $ | |align=right| $6,400 | ||
|align=right| $ | |align=right| $6,400 | ||
|align=right| $ | |align=right| $7,900 | ||
|- | |- | ||
|} | |} | ||
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7a11-probe-interior-back.jpg| interior of probe, back side with range relays | 7a11-probe-interior-back.jpg| interior of probe, back side with range relays | ||
Tek 7a11 on.JPG | Tek 7a11 on.JPG | ||
Tek 7a11 probe.jpg|Probe | |||
Tek 7a11 input amplifier.jpg|Input Amplifier | |||
Tek 7a11 output amplifier.jpg|Output Amplifier | |||
Tek 7a11 offset generator.jpg|Offset Generator | |||
Tek 7a11 volts-per-div switch and readout.jpg|Volts/Div Switch and Readout | |||
Tek 7a11 power supply and output connectors.jpg|Power Supply and Output Connectors | |||
</gallery> | </gallery> | ||
==Components== | |||
{{Parts|7A11}} | |||
[[Category:7000 series vertical plugins]] | [[Category:7000 series vertical plugins]] | ||
[[Category:Active oscilloscope probes]] | [[Category:Active oscilloscope probes]] |