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IM CANCELLATION TECHNIQUE

IP.com Disclosure Number: IPCOM000005807D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2001-Nov-08
Document File: 2 page(s) / 80K

Publishing Venue

Motorola

Related People

Ralph T. Enderby: AUTHOR

Abstract

What is presented is a design technique that when used when designing a mixer or amplifier circuit can help reduce the non-linear characteristics inherent in such circuits, and the IM and distortion associated with them. At the same time consideration is given to the noise figure, and power gain.

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MOTVROLA Technical Developments Volume 9 August 1989

IM CANCELLATION TECHNIQUE

by Ralph T Enderby

PURPOSE OF DISCLOSURE:

   What is presented is a design technique that when used when designing a mixer or amplifier circuit can help reduce the non-linear characteristics inherent in such circuits, and the IM and distortion associated with them. At the same time consideration is given to the noise figure, and power gain.

BASIC IDEA:

It is well known that the IM of an amplifier or mixer depends on the degree of nonlinearity of the active device. If this nonlinearity is described as a power series, e.g. if the output voltage is related to the input as:

v ou = ao+aIVin+a2V;Z,+ajV?, +... Eq. 1

then the a, term contributes to the IM. The exact degree that it contributes can be shown to be:

Ih4 DE = $%I,- $vinI, Eq. 2

   It is also known that the circuit that the non-linearity is "imbedded" into effects the non-linearity of the total circuit as viewed by the source and load nodes. For example, consider the simple circuit below where the non-linearity is described by Eq 1.

Lineai Resistance

Non-linear element given by Eq.1

Now a new power series can be derived between the source generator, wn, and the output voltage across the non-linear element, vO.,. This new power series gives rise to a new expression for IM expressed as:

I& =L arCa& + 1j4 - 'Vi,

Eq. 3

Note that now the IM is now dependant on the value of the resistance in addition to the coefficients of the non-linear element.

This fact (that the IM is effected by the linear circuit elements) can be used to improve the IM of a circ...