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Distributed amplifier: Difference between revisions
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==Solution== | ==Solution== | ||
[[File:Distributed amplifier principle. | [[File:Distributed amplifier principle.png|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". | ||
is a "transmission line with gain". The gain is the sum (not the product) | The gain is the sum (not the product) of the gains of the stages, whereas the bandwidth of a distributed amplifier is the bandwidth of each of the stages. | ||
of the gains of the stages, whereas the bandwidth of a distributed amplifier is | |||
the bandwidth of each of the stages. | |||
Thus, it is possible to construct an amplifier with a gain of 100 and a rise time of 3 ns | Thus, it is possible to construct an amplifier with a gain of 100 and a rise time of 3 ns | ||
by using ten instances of the ×10, 3 ns amplifier from the earlier example connected to | by using ten instances of the ×10, 3 ns amplifier from the earlier example connected to form a distributed amplifier. | ||
form a distributed amplifier. | |||
The key difference between a distributed conventional cascaded-stage amplifier is that | The key difference between a distributed conventional cascaded-stage amplifier is that in the former, | ||
in the former, the input of each stage is the original signal, not the output of a | the input of each stage is the original signal, not the output of a previous stage, thus eliminating | ||
previous stage, thus eliminating the cumulative degradation of rise time that occurs in | the cumulative degradation of rise time that occurs in cascaded stages. | ||
cascaded stages. | |||
One of the most important challenges when building distributed amplifiers is avoiding reflections in the signal path. | |||
For example, when the input signal reaches the input of one stage, parasitic capacitance of that stage must not | |||
cause an impedance discontinuity 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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==History== | ==History== | ||
[[File:Tek513-dist-amp.jpg|thumb|250px|right|Symmetrical distributed amplifier in [[513]] scope]] | |||
The idea of a distributed amplifier goes back to [[Patent GB 460562A|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 | The [[581|580 series]] (1959) were the last Tektronix scopes to use distributed amplifiers. | ||
==See also== | ==See also== | ||
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==Products== | ==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 == | ||
* [ | * [[wikipedia:Distributed_amplifier|Distributed Amplifier]] @ Wikipedia | ||
* W. S. Percival, [[Patent GB 460562A|British Patent Specification No. 460,562, ''Improvements In and Relating to Thermionic Valve Circuits'']], Filed 24 Jul 1936, granted 2 Jan 1937 | |||
* John Addis, ''Good Engineering and Fast Vertical Amplifiers'', in Jim Williams (Ed.), ''Analog Circuit Design: Art, Science and Personalities'' (1991), p.110 | * E. L. Ginzton, W. R. Hewlett, J. H. Jasberg, J. D. Noe, “Distributed Amplification”, Proceedings of the IRE, pp 956-969, August 1948. | ||
* [[John Kobbe]] and [[Bill Polits]], [[Patent US 2930986A|US Patent 2,930,986, ''Distributed Amplifier'']]. Filed 29 Feb 1956, granted 29 Mar 1960. | |||
* [[John Addis]], ''Good Engineering and Fast Vertical Amplifiers'', in Jim Williams (Ed.), ''Analog Circuit Design: Art, Science and Personalities'' (1991), p.110 | |||
* G.Nikandish, R.Staszewski and A.Zhu, ''[https://hertz.ucd.ie/publications/DA_Review.pdf The (R)evolution of Distributed Amplifiers: From Vacuum Tubes to Modern CMOS and GaN ICs]''. IEEE Microwave Magazine Vol. 19 Issue 4, June 2018, p.66+ | |||
<gallery> | |||
Tek 545 distributed amplifier on.jpg|Distributed vertical amplifier in [[545]] | |||
Tek_555_V-Amp.jpg | Distributed vertical amplifier in [[555]] | |||
</gallery> | |||
[[Category:Circuits and Concepts]] | [[Category:Circuits and Concepts]] | ||