Did Deane Jensen "Invent" The Emitter Inductor?

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Did Deane Jensen "Invent" The Emitter Inductor?

Post by mediatechnology » Tue Aug 26, 2014 4:40 pm

Did Deane Jensen "Invent" The Emitter Inductor?

Maybe not, but he did patent it. From the 1981 Jensen Patent:
The reactive network associated with each emitter element preferably comprises an inductor and a resistor, coupled in a shunt configuration. Thus, at relatively high frequencies, the impedance of the network is roughly equivalent to that of the resistor and the gain of the stage is determined by the sum of each resistor and the internal emitter resistance re of the corresponding transistor, while at relatively low frequencies, the network impedance is essentially zero and the gain of the stage is determined by the internal emitter resistance re, by itself. As a result, for frequencies less than the frequency at which the emitter resistor and inductor are equal in impedance, the stage will produce less noise and will provide an increased open-loop gain, whereby less distortion of the signal is realized. Additionally, since the presence of the inductor does not affect the impedance of the network at relatively high frequencies, i.e., at frequencies near the unity-gain frequency, ft, of the op amp circuit, stability of the circuit is not adversely affected thereby.
The "Jensen" Patent US 4,287,479: http://www.google.com.ar/patents/US4287479

Image
Jensen 1981 Patent, Figure 2, Showing Emitter Inductors

In 1966 Dick Burwen of Analog Devices designed the ADI Model 121 "Wideband DC Op Amp" with, you guessed it, emitter inductors.

Image
Analog Devices ADI Model 121 Wideband Op Amp Designed by Dick Burwen in 1966 with Shunted Emitter Inductors.
Image Courtesy of Analog Devices and Walt Jung, "Op Amp Applications Handbook."


Note the simple bias current cancellation used in the ADI 121.

See also: http://www.analog.com/library/analogDia ... _final.pdf

Prior Art? We report, you decide.
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