Browse Prior Art Database

VOLTAGE CONTROLLED FILTER

IP.com Disclosure Number: IPCOM000005848D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-12
Document File: 3 page(s) / 101K

Publishing Venue

Motorola

Related People

Peter Yeh: AUTHOR [+2]

Abstract

There is an increasing demand by users for a radio that is capable of receiving multiple channels whose frequen- cies are spread across the band. This would enable users (like state and local governmental agencies) to communicate with each other (e.g., in an emergency situation) with the same radio.

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MOTOROLA Technical Developments Volume 10 March 1990

VOLTAGE CONTROLLED FILTER by Peter Yeh and Bob Stengel There is an increasing demand by users for a radio that is capable of receiving multiple channels whose frequen- cies are spread across the band. This would enable users (like state and local governmental agencies) to communicate with each other (e.g., in an emergency situation) with the same radio.

   To meet the challenge, radios must have wider bandwidths. The wider the bandwidth, the fewer the number of bandsplits required. However, this means that for the receiver frontend, a preselector filter is needed that is either very broadband or a filter that is tunable across the whole band. The former would also require a much higher IF frequency in order to satisfy selectivity requirements. The SABER UHF preselector filters for example, have a bandwidth of 30 MHZ and this required 5 bandsplits to cover the UHF band from 400 MHZ to 520 MHZ.

   The Voltage Controlled Filter (VCF) on the other hand, is a tunable filter capable of covering the VHF or the UHF band in one filter. The VCF is a basic two mesh network consisting of two resonant circuits. The mesh circuit has undergone a Y to n transformation and back-to-back varactor diodes are used.

This configuration was chased to provide the following features:
I. OPTIMIZED DC FLOW

Figure 1

RF IN

Voltage Controlled Filter The VCF topology provides a path for the DC without using additional components.
II. IMPROVED DISTORTION Back-to-back varactor diodes in a common cathode configuration provides the improvement in distortion [I]

0 Motorola, Inc. 1990 37

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MOTOROLA Technical Developments

Ill. REDUCED EFFECT OF STRAY CAPACITANCE

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Volume 10 March 1990

T T Figure 2 (a) Figure 2 (b)

The VCF has minimum stray capacitance which can be tuned...