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Distributed amplifier: Difference between revisions
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where t<sub>r1</sub> is the risetime of the first amplifier and t<sub>r2</sub> that of second amplifier. | where t<sub>r1</sub> is the risetime of the first amplifier and t<sub>r2</sub> that of second amplifier. | ||
For example, cascading two amplifiers having a gain of 10 and a rise time of 3 ns, and a gain of 12 and a rise time of 4 ns, respectively, will result in a mid-band gain of 120 and a rise time of 5 ns. | For example, cascading two amplifiers having a gain of 10 and a rise time of 3 ns, and a gain of 12 | ||
and a rise time of 4 ns, respectively, will result in a mid-band gain of 120 and a rise time of 5 ns. | |||
Consider a designer who is working with a technology that produces | Consider a designer who is working with a technology that produces | ||
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==Solution== | ==Solution== | ||
[[File:Distributed amplifier principle.jpg|thumb| | [[File:Distributed amplifier principle.jpg|thumb|400px|right|Distributed amplifier principle]] | ||
In a distributed amplifier, several stages are connected together to form what in effect | In a distributed amplifier, several stages are connected together to form what in effect | ||
is a "transmission line with gain". The gain is the sum (not the product) | is a "transmission line with gain". The gain is the sum (not the product) | ||
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of one stage, parasitic capacitance of that stage must not cause an impedance discontinuity | of one stage, parasitic capacitance of that stage must not cause an impedance discontinuity | ||
in the signal path, which would cause reflection. | in the signal path, which would cause reflection. | ||
[[File:Tek 581 vertical output amp.png|thumb|right|400px| [[581|Tektronix 581]] distributed vertical amplifier schematic (click to enlarge)]] | |||
Since eliminating the parasitic capacitance is not possible, the approach is usually to | Since eliminating the parasitic capacitance is not possible, the approach is usually to | ||
reduce the capacitance of the transmission line around each amplifier input (thereby | reduce the capacitance of the transmission line around each amplifier input (thereby | ||
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energy loss in the transmission line, which limits the number of stages. | energy loss in the transmission line, which limits the number of stages. | ||
==History== | |||
[[File:Tek513-dist-amp.jpg|thumb|250px|right|Symmetrical distributed amplifier in [[513]] scope]] | |||
The idea of a distributed amplifier goes back to British Patent 460,562 by W.S. Percival in 1936. | |||
In 1948, Ginzton, [[Bill Hewlett|Hewlett]], Jasberg and Noe published a paper on distributed amplifiers in the Proceedings of the IRE, first using the term "distributed amplifier". Around the same time, Hewlett met [[Logan Belleville]] of Tektronix in a Portland restaurant and described the concept on a napkin. In the fall of 1948, [[Howard Vollum]] and [[Dick Rhiger]] built a 6 ns rise time distributed amplifier under a US government contract (for radar applications). The prototype was attached externally to an early [[511]] oscilloscope. | |||
Vollum, Belleville and Rhiger went on to design the 50 MHz [[517]] oscilloscope incorporating a distributed vertical amplifier. | |||
The [[581|580 series]] (1959) were the last Tektronix scopes to use distributed amplifiers. | |||
==See also== | |||
* [[Distributed deflection plates]] | |||
==Products== | |||
[[File:585a_dist_vert_amp.jpg|thumb|250px|right|Second distributed amplifier in [[585A]] scope]] | |||
These Tektronix instruments contain distributed amplifiers: | These Tektronix instruments contain distributed amplifiers: | ||
<div style="column-count:8;-moz-column-count:8;-webkit-column-count:8"> | <div style="column-count:8;-moz-column-count:8;-webkit-column-count:8"> | ||
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* [[585]] | * [[585]] | ||
* [[82]] | * [[82]] | ||
* [[86]] | |||
* [[945]] | * [[945]] | ||
</div> | </div> | ||
== Reading == | == Reading == | ||
* [http://w140.com/US2930986.pdf US Patent 2,930,986]: [[John Kobbe|J. R. Kobbe]], "Distributed Amplifier" | * W. S. Percival, British Patent Specification No. 460,562, ''Improvements In and Relating to Thermionic Valve Circuits'', applied for, July 24, 1936, granted January 1937 | ||
* E. L. Ginzton, W. R. Hewlett, J. H. Jasberg, J. D. Noe, “Distributed Amplification”, Proceedings of the IRE, pp 956- 969, August 1948. | |||
* [http://w140.com/US2930986.pdf US Patent 2,930,986]: [[John Kobbe|J. R. Kobbe]] and [[Bill Polits|W. J. Polits]], "Distributed Amplifier". Applied 29 Feb 1956, granted 29 Mar 1960. | |||
* [http://en.wikipedia.org/wiki/Distributed_amplifier Wikipedia: Distributed Amplifier] | |||
* [[John Addis]], ''Good Engineering and Fast Vertical Amplifiers'', in Jim Williams (Ed.), ''Analog Circuit Design: Art, Science and Personalities'' (1991), p.110 | |||
[[Category:Circuits]] | <gallery> | ||
Tek 545 distributed amplifier on.jpg|Distributed vertical amplifier in [[545]] | |||
</gallery> | |||
[[Category:Circuits and Concepts]] | |||