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High Input Impedance Voltage Follower

IP.com Disclosure Number: IPCOM000083630D
Original Publication Date: 1975-Jun-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Commander, RD: AUTHOR

Abstract

A method of increasing preamplifier input impedance is described in the article entitled "Magnetic Head Preamplifier" by R. D. Commander, appearing in the IBM Technical Disclosure Bulletin, Vol. 17 No. 5 October 1973 pages 1657 and 1658. The above figure shows the relevant part of the circuit illustrating how this technique is applied to a voltage follower.

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High Input Impedance Voltage Follower

A method of increasing preamplifier input impedance is described in the article entitled "Magnetic Head Preamplifier" by R. D. Commander, appearing in the IBM Technical Disclosure Bulletin, Vol. 17 No. 5 October 1973 pages 1657 and 1658. The above figure shows the relevant part of the circuit illustrating how this technique is applied to a voltage follower.

In the figure, transistors T1, T2 and current source 1 provide a conventional input stage for a voltage follower shown schematically as block 2. The INVERT input to transistor T2 is fed from the voltage follower output terminal 3. Provided that transistors T1 and T3 are fabricated on the same integrated circuit chip, they will have the same base currents. This base current is reflected in a current mirror consisting of transistors T4 and T5 and fed into the base of transistor T1.

Thus the current to be supplied from the input terminal 4 is nominally zero, although in practice it will be positive or negative depending on transistor tolerances. This will not matter, however, provided the impedance of the driving stage is low, as is often the case with voltage-follower applications.

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