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THE USE OF TRANSFORMERS AND INDUCTIVE ELEMENTS INTEGRATED ACTIVE MIXER CIRCUITS

IP.com Disclosure Number: IPCOM000009852D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-24
Document File: 2 page(s) / 85K

Publishing Venue

Motorola

Related People

Ralph C. Denig: AUTHOR

Abstract

Active transistor mixers have become very popular integrated circuit components due to the fact that they can provide conversion gain, operate with low LO drive levels, and provide excellent port-toport isolation. They are plagued by some problems, however, such as relatively high noise figure and mediocre linearity performance.

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MOTOROLA

Technical Developments

THE USE OF TRANSFORMERS AND INDUCTIVE ELEMENTS INTEGRATED ACTIVE MIXER CIRCUITS

by Ralph C. Denig

Active transistor mixers have become very popular integrated circuit components due to the fact that they can provide conversion gain, operate with low LO drive levels, and provide excellent port-toport isolation. They are plagued by some problems, however, such as relatively high noise figure and mediocre linearity performance.

With the advent of low-Ioss copper metallization, though, many advantageous RF circuit configurations of analog balanced mixers address these problem areas and can be realized with on-chip transformers and inductors.

A circuit configuration that results in exceptionally good gain and noise figure performance is illustrated in Figure 1. In this circuit, a copper transfonner is placed between the input device and the switching devices of a bipolar mixer. The transfonner in this location enables the use of a singleended input device, which lowers the noise figure as compared to a differential input.

The transfonner also DC isolates the mixer seclions, allowing the mixer to operate at lower supply voltages since the full supply voltage appears across each section instead of being divided between the sections. Also, the load impedance seen by the input transistor can be made higher than in a conventional cascode circuit, which also improves the gain and noise figure perfomlance of the mixer.

Motorola, Inc. 2000

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Fig. 1 Bipolar Mixer Schematic with Transfonner

Another excellent application for an on-chip transfonner...