Browse Prior Art Database

MOSFET CIRCUIT SENSES DCV ON RF COAX TO KEY REMOTE AMPLIFIER

IP.com Disclosure Number: IPCOM000005972D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-21
Document File: 2 page(s) / 76K

Publishing Venue

Motorola

Related People

Robert B. Ford: AUTHOR

Abstract

A remote amplifier amplifies the RF output of a transmitting portable radio. A coaxial path between the portable radio and amplifier serves as the RF signal path as well as the control signal path. When the portable is in the receive- mode, the remote amplifier has a thmugh RF path for the antenna receive signals to be passed on to the portable receiver. When the portable is in the transmit-mode, the coaxial path is replaced with the amplifier circuit. The switching of these paths is done by a TX detect circuit which is the subject of this disclosure.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 58% of the total text.

Page 1 of 2

69 MO7WROLA

Technical Developments Volume 11 October 1990

MOSFET CIRCUIT SENSES DCV ON RF COAX TO KEY REMOTE AMPLIFIER

by Robert B. Ford

   A remote amplifier amplifies the RF output of a transmitting portable radio. A coaxial path between the portable radio and amplifier serves as the RF signal path as well as the control signal path. When the portable is in the receive- mode, the remote amplifier has a thmugh RF path for the antenna receive signals to be passed on to the portable receiver. When the portable is in the transmit-mode, the coaxial path is replaced with the amplifier circuit. The switching of these paths is done by a TX detect circuit which is the subject of this disclosure.

Some portable radios (Motorola MTX series) indicate transmit mode by raising a DC voltage on the center conduc- tor of an outgoing RF coaxial cable.

   The TX detect circuit described in this disclosure is used to sense the DC voltage level on this coaxial path and to change its state. The circuit is required to change its output logic state upon application of the DC voltage, but not impact the RF impedance of the coaxial path. The detection must be consistent and not false, even within a strong RF field environment.

   Traditionally this circuit function has been implemented with Bipolar Junction transistoffi (SJTs). To achieve accep table performance with BJTs. the parts count (and therefore cost and opportunity for defects) would exceed that of the disclosed circuit. The disclosed T-...