Browse Prior Art Database

BROADBAND ACTIVE BALANCED MIXER

IP.com Disclosure Number: IPCOM000005567D
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2001-Oct-16
Document File: 4 page(s) / 125K

Publishing Venue

Motorola

Related People

Alan M. Victor: AUTHOR

Abstract

Today's communication products demand increased operating bandwidth. Both the receiver and transmitter circuits require a greater percentage tuning range and without improved circuit design a degredation in spurious performance can occur.

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@ MOTOROLA

Technical Developments Volume 5 October 1985

BROADBAND ACTIVE BALANCED MIXER

by Alan M. Victor

   Today's communication products demand increased operating bandwidth. Both the receiver and transmitter circuits require a greater percentage tuning range and without improved circuit design a degredation in spurious performance can occur.

   Broadband receivers have two particularly troublesome spurious. The first is related to distortion in the mixer due to closely spaced strong carrier signals (third order I.M.) and the second is due to an even order distortion product known as the half IF. spurious. The half IF. spurious is normally reduced in level by providing adequate front end filtering. As the receiver bandwidth increases though more and more of the rejection must be obtained from the mixer itself. This rejection in the mixer is obtained by properly balancing the mixer RF. or L.O. ports and always balancing the output port or the I.F. port of the mixer.

Proper amplitude and phase balance of the L.O. and RF. signals provides an improvement in the half I.F. spurious rejection level given by:

l/2 I.F. improvement dB = 10 log((l-cos O)/(l-cos 2 0)) dB

Other benefits in proper balance are decreased L.O. conducted energy and L.O. phase noise reduction ap- pearing at the I.F. port.

   Two designs are presented. The VHF design (Figure 1) utilizes a common gate balanced JFET configuration for stability while the UHF (Figure 2) uses the common source arrangement for improved gain. In order to achieve even order distortion improvement the FET devices are driven in a balanced fashion either push-push by the L.O. and push-pull by the RF. or vice-versa. The I.F. port connection (FET drain current) must be connected in push- pull fashion. If L.O. noise balance is to be achieved, then the proper connection is to have the L.O. applied in push- push and the R.F. applied in push-pull. The degree of balance is only achieved if the entire network is properly balanced, both in amplitude as well as phase. The degree of half IF balance is related in a 2:l manner so that a 2 dB improvement i...