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GaAs SWITCHING MIXER WITH DUAL GATES FOR SIGNAL AND INJECTION GAIN CONTROL

IP.com Disclosure Number: IPCOM000005915D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-15
Document File: 3 page(s) / 102K

Publishing Venue

Motorola

Related People

Yolanda Prieto: AUTHOR [+4]

Abstract

In a Depletion dual gate MESFET the magnitude and linearity of the transconductance, gm, varies as the gate two-to-source voltage (Vgs2) changes. A similar phenomenon is obtained as Vgsl changes.

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MOTOROLA Technical Developments March 1990

GaAs SWITCHING MIXER WITH DUAL GATES FOR SIGNAL AND INJECTION GAIN CONTROL

by Yolanda Prieto, Patricia Mayor, John Wayne Simmons and Edward T. Clark

In a Depletion dual gate MESFET the magnitude and linearity of the transconductance, gm, varies as the gate two-to-source voltage (Vgs2) changes. A similar phenomenon is obtained as Vgsl changes.

   In the following example mixer circuits the gates 1. (Vx) and (Vy) voltages control mostly the signal path and the injection paths respectively. The d.c. voltages Va and Vb set the optimum bias point to operate the dual gate FETs as a transconductance mixer. Thus, the operating point for the mixer must be such that the variation by the local oscillator voltage changes the transconductance of the FET as much and as linear as possible. By carefully selecting the injection drive and properly selecting the bias of the top device gate 2 d.c. voltage (Va) one can select the device operation where the transconductance exhibits the most linear change with gate bias, thus minimizing the third order distortion product term. Also, by varying the voltages Va and Vb, the mixer conversion gain can be controlled.

It can be observed from attached Fig. 1 how the transconductance is increased and linearized as Vgs2 increases. This provides a controlled gain while optimizing the mixer intermodulation distortion performance.

It is well known that the magnitude of 512 of dual gate devices is reduced from those of single gates. Therefore, in addition, this mixer architecture provides improved LO-IF, RF-IF and RF-LO isolation.

The advantages of the mixers in figures 2, 3 and 4...