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Inverting Function Generation

IP.com Disclosure Number: IPCOM000074460D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Ottesen, H: AUTHOR

Abstract

The reciprocal function of a selected number has been a complex operation whether using analog or digital techniques. This hybrid circuit provides a reciprocal function with a small number of components at a relatively high speed. The circuit may be integrated.

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Inverting Function Generation

The reciprocal function of a selected number has been a complex operation whether using analog or digital techniques. This hybrid circuit provides a reciprocal function with a small number of components at a relatively high speed. The circuit may be integrated.

Operational amplifier 10 receives a reference input through resistor 11. Resistor 12 provides voltage feedback preventing saturation of operational amplifier 10. Output voltage VO is taken from terminal 13. A voltage feedback loop is provided by DAC 14 which has its output circuit connected between terminal 13 and summing junction 15 at the input of amplifier 10.

The digital input number, K, is inserted into register 16 which, in turn, controls the output portion of the DAC represented by a plurality of switches 17 with corresponding weighted resistors 18. The resultant feedback resistance through selected resistors 18 represents the number in register 16. Analysis shows that the output voltage, VO, is represented by the equation set forth in the drawing
(i.e., a reciprocal of the input number).

It will be immediately recognized that this equation is a good approximation for a power series used in integration techniques. By inserting the number (K-1) into register 16, true reciprocal of the number K(in) is obtained.

K(1) and K(2) are functions of resistors 11, 12 and characteristic ladder impedance in 18. A current mode DAC can be used with the same results as obtained for the...