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AUTOMATIC REFERENCE OSCILLATOR TUNING STRATEGY

IP.com Disclosure Number: IPCOM000005846D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-12
Document File: 2 page(s) / 120K

Publishing Venue

Motorola

Related People

Cesar Carralero: AUTHOR [+2]

Abstract

The Automatic Reference Oscillator Tuning Strategy (AROTS) is designed to adjust the portable's synthesized first oscillator (1st LO) frequency to match the received signal within a predefined channel spacing. This frequency correction capability for receive mode can be used during transmit via sample-and-hold circuitry or can be disabled to allow transmission at the predefined nominal frequency. These features allow for optimization of the transceiver's operation, thereby providing for reduced distortion and improved sensitivity over a wider range of the assigned channel spacing. AROTS based techniques would also be a simple but effective means in compensating for Doppler frequency shifts in transmitted signals from satellites in non-geosynchronous orbits. This may be of some value when implement- ing a satellite-based national coverage communication network. The main advantage would be the ability to use less expensive reference oscillators which can be retuned internally by monitoring a control channel (ie: trunked systems) and adjusting the reference oscillator via p p control. This could result in significant cost savings while not compromis- ing the tolerance required for the reference oscillator. The Automatic Reference Oscillator Tuning Strategy is illustrated in Figure 1.

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MOTOROLA Technical Developments Volume 10 March 1990

AUTOMATIC REFERENCE OSCILLATOR TUNING STRATEGY

by Cesar Carralero and Charles Ruelke

local

The Automatic Reference Oscillator Tuning Strategy (AROTS) is designed to adjust the portable's synthesized first oscillator (1st LO) frequency to match the received signal within a predefined channel spacing. This frequency correction capability for receive mode can be used during transmit via sample-and-hold circuitry or can be disabled to allow transmission at the predefined nominal frequency. These features allow for optimization of the transceiver's operation, thereby providing for reduced distortion and improved sensitivity over a wider range of the assigned channel spacing. AROTS based techniques would also be a simple but effective means in compensating for Doppler frequency shifts in transmitted signals from satellites in non-geosynchronous orbits. This may be of some value when implement- ing a satellite-based national coverage communication network. The main advantage would be the ability to use less expensive reference oscillators which can be retuned internally by monitoring a control channel (ie: trunked systems) and adjusting the reference oscillator via p p control. This could result in significant cost savings while not compromis- ing the tolerance required for the reference oscillator. The Automatic Reference Oscillator Tuning Strategy is illustrated in Figure 1.

Figure 1. Automatic Reference Oscillator Tuning Strategy block diagram.

   The strategy utilizes the control voltage from the base band demodulator's PLL in the receiver's back end as a control voltage for tuning the 1st LO. This technique is more effective than tuning the 2nd LO frequency (in dual injection receivers) as the symmetry between the 1st IF and 2nd IF filters is maintained. After filtering the demodulators output through a low pass filter, the DC control voltage is fed directly into the noninverting terminal of a differential amplifier whose gain has been set to accommodate the modulatable reference oscillator. The A p factory set to tune the reference voltage (D/A converter output) to the required level in order to achieve the nominal reference oscillator frequency while receiving a known carrier frequency. The voltage difference between the demodulator's control voltage and the D/A reference voltage is stored in the A p. This configuration will perform properly for standby and receive mode operation. For transmit operation, the control voltage must be sourced from a predefined reference voltage or a sample-and-hold circuit since the demodulator's PLL free runs at an arbitrary frequency when transmitting. Auto-tuning is achieved while

0 Motorola, Inc. 1990 34

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MOTOROLA Technical Developments Volume 10 March 1990

monitoring a pred...