US 6,161,003 AGranted

Automatic local oscillator frequency stabilization process in radio receivers employing a wide-band tunable local dielectric-resonator oscillator and associated device

AssigneeItaltel S.p.A.

InventorsMichelangelo Lo Curto, Giuseppe De Marzi, Giuseppe Dimonte

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Abstract

There is described a stabilization process for the local oscillator frequency in wide-band tunable DROs employed in receivers of a digital microwave radio link. A microprocessor, already provided for normal operation control, cyclically reads the control voltage of a VCO inserted in PLL which reconstructs an intermediate frequency carrier used to coherently demodulate the received signal. The voltage read is compared with an optimal reference value by taking an error signal which controls a varicap diode of the DRO for tuning correction. With each reading, the optimal value can be modified on the basis of temperature data supplied by a heat sensor to cancel the effect of temperature on the reference.

Claims15

Dependent claims

Automatic local oscillator frequency stabilization process in radio receivers employing a local oscillator with a wide-band tunable dielectric resonator providing an oscillation frequency to an intermediate frequency converter of the receiving signal, the intermediate frequency supplied by said intermediate frequency converter reaching a demodulator including a Voltage Controlled Oscillator (VCO) inserted in a Phase-Locked Loop (PLL) for reconstruction of an intermediate frequency carrier (f.sub.i) used for demodulation, with said local oscillator including manual and electronic tuning means acting on which a desired receiving channel is tuned initially, comprising an initial step of memorization of a voltage V.sub.ott considered optimal for control of said VCO, with said optimal value being such that if used for control of the VCO virtually excluded from the PLL and under nominal temperature conditions it would make it oscillate freely at the nominal value of said intermediate frequency (f.sub.i);

and the following steps repeated cyclically:
a) conversion into digital form of the present value of the VCO control voltage (V.sub.VCO);
b) comparison of said present value (V.sub.vco) of the VCO control voltage with said optimal value V.sub.ott to obtain an error signal indicative of a frequency deviation of said intermediate frequency carrier (f.sub.i) from said nominal value thereof;
and
c) comparison of the absolute value of said error signal with art appropriate positive threshold the exceeding of which generates a criterion valid for inclusion in a cycle of a following step,
d) in which said error signal is converted into analog form and used to command an electronic tuning change of said local oscillator with the direction and amount of said change being such as to cancel out said error signal.

3 more elements

The automatic local oscillator frequency stabilization process in accordance with any one of the above claims, wherein said positive threshold used in step c) takes a first value on persisting of a `start` condition which first causes seeking of the locking of said PLL and then optimization of the value of said intermediate frequency carrier (f.sub.i), with said `start` condition beginning with energizing of said radio receiver or with an expiration of a maximum time during which said PLL is not in a locking condition;

said positive threshold taking a second value higher than said first value on persisting of a condition of `normality` replacing said `start` condition or replacing an `alarm` condition generated by loss of locking of said PLL due to cessation thereof.

An automatic stabilization device for a local oscillator frequency in radio receivers comprising a local oscillator with a wide-band tunable dielectric resonator providing the oscillation frequency to an intermediate frequency converter of a receiving signal, the intermediate frequency supplied by said intermediate frequency converter reaching a demodulator including a Voltage Controlled Oscillator (VCO) inserted in a Phase-Locked Loop (PLL) for reconstruction of an intermediate frequency carrier (f.sub.i) used for demodulation, and a microprocessor (PROC) for operation supervision;

with said local oscillator including manual and electronic tuning means adjusting which a desired receiving channel is initially tuned, comprising:
means of memorizing a voltage value V.sub.ott considered optimal for control of said VCO, with said optimal value being such that if used for control of the VCO, virtually excluded from the PLL and under nominal temperature conditions, it would make it oscillate freely at the nominal value of said intermediate frequency (f.sub.i);
means of analog-digital conversion of the present value of the VCO control voltage (V.sub.vco);
processing means (PROC) for generation of change of a numerical magnitude representative of a control voltage (V.sub.dro) for said electronic tuning means;
and said processing means (PROC), a) acquire at preset times the present values of said VCO control voltage (V.sub.vco) and compare them with said optimal memorized value V.sub.ott to obtain an error signal indicative of the deviation in frequency of said intermediate frequency carrier (f.sub.i) from said nominal value thereof, and b) compare the absolute value of said error signal with an appropriate positive threshold the exceeding of which results in a change in said control voltage (V.sub.dro) of said electronic tuning means with the direction and amount of said change being such as to cancel out said error signal.

2 more elements

Dependencies are inferred from the claim text.