Browse Prior Art Database

FAST LOCK TIME FRONT END FOR T.D.M

IP.com Disclosure Number: IPCOM000005717D
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2001-Oct-30
Document File: 1 page(s) / 61K

Publishing Venue

Motorola

Related People

Jose I. Suarez: AUTHOR

Abstract

For aTime Domain Multiplexed communication channel, using vector modulation (i.e., quadruture carriers), it is required to switch from receive to transmit, and viceversa, in a fraction of the frame time; this amounts to sub-milisecond switching. It is also required, while in transmit mode, to provide isolation to the receiver I.F. filter, so as to reduce any stored energy in said filter.

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MOlYIROLA Technical Developments Volume a October 1989

FAST LOCK TIME FRONT END FOR T.D.M.

by Jose I. Suarez

   For aTime Domain Multiplexed communication channel, using vector modulation (i.e., quadruture carriers), it is required to switch from receive to transmit, and viceversa, in a fraction of the frame time; this amounts to sub-milisecond switching. It is also required, while in transmit mode, to provide isolation to the receiver I.F. filter, so as to reduce any stored energy in said filter.

   The circuitry shown in the block diagram accomplishes the desired functions. In order to acquire lock quickly the frequency synthesizer @M/N) block does not change frequency; the transmitter carrier is generated via an offset loop, using the same VCXO as in the receiver loop. The receiver loop contains a means of storing the latest turning voltage for the the VCXO; this means consists of a track-and-hold amplifier, for the analog im- plementation, or an ADClDAC combination with a memory device for digital implementation. In the receiver mode, the carrier tuning information is contained in the in-phase demodulated carrier(P). In transmit mode, the storing means goes into hold mode, which must be accomplished with minimal transient feedthrough. The single transmit/receive control signal must set hold mode before disabling the receive loop. Also both quadrature carriers must be provided: this is done using a special quadrature VCO ring oscillator, consisting of two iden-...