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The Design of Ultra-high Quality Feedback Amplifiers

Citation Author(s):
Robert E. Rouquette
Submitted by:
Robert E. Rouquette
Last updated:
7 June 2023 - 11:21am
Document Type:
Student Thesis
 

___Although dated, this student thesis is re-published as the proposed negative feedback topology and the current mode arrangement of silicon bipolar junction transistors is rarely elaborated in the many excellent contemporary books on audio power amplifier design.
___This paper presents suggestions for reducing high frequency non-linear distortion below the levels achieved in present (circa 1974) commercial audio power amplifiers. The commercial amplifiers fail to maintain sufficient negative feedback at the higher working frequencies. Transfer functions are proposed which maintain high negative feedback, with good stability margins, over the entire range of working frequencies, keeping distortion products below a desired design level. The performance of a prototype amplifier using the proposed transfer functions is documented and compared with high quality commercial units. The high frequency non-linear distortion of the prototype amplifier is less than that of the best commercial amplifiers.
___In the circuits presented in this paper, an attempt has been made to utilize silicon bipolar junction transistors to their best advantage. Current mode operation, that is current sources driving low impedances, is used wherever possible. This technique results in good high frequency response, low non-linear distortion, good thermal stability, and high PSRR. The circuits presented, when made to realize the transfer functions proposed, result in an ultra-high-quality amplifier.
___With a career of 50 years elapsed, the author is aware of the additional circuit elements needed to develop this concept into a practical reliable amplifier and is not soliciting comment on these matters.

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