Radio receiver capable of temperature adjustment to tuning...

Details Radio receiver capable of temperature adjustment to tuning... Radio receiver capable of temperature adjustment to tuning...

1998-03-25

2001-06-05

Trost, William G. (Department: 2683)

Telecommunications

Receiver or analog modulated signal frequency converter

With particular receiver circuit

C455S184100, C455S193300

Reexamination Certificate

active

06243570

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio receiver that corrects a tuning frequency of an RF tuning circuit on the basis of a frequency of a desired station and characteristics of a tuning element in the RF tuning circuit.
2. Description of the Related Art
Radio receivers normally include a means for preventing tracking error, which is the deviation between a tuning frequency of an RF tuning circuit and a frequency of an RF signal to be converted to a desired IF signal at a mixer circuit. A means has been proposed for correcting the RF tuning frequency in such radio receivers while taking into consideration the characteristics of a varicap diode as well as a coil constituting the RF tuning circuit. Such a radio receiver may be configured as shown in
FIG. 1
, and the tuning frequency of the RF tuning circuit is corrected according to the flowchart of FIG.
2
.
In
FIG. 1
, the received RF signal is amplified by an RF amplifier
1
, then tuned by an RF tuning circuit
2
. The tuned RF signal is converted in frequency at a mixer
3
with a local oscillation signal from a local oscillator
4
to an IF signal having, for example, a center frequency of
10
.
7
MHz. The IF signal is amplified by an IF amplifier
5
, then searched for FM at an FM detector
6
.
An operation to set the tuning frequency of the RF tuning circuit
2
will be described next with reference to the flowchart of FIG.
2
. First, the frequency of a local oscillation signal is set by a local oscillation control signal “a” of a controller
7
. The frequency of the local oscillation signal is set so that the IF signal corresponding to the frequency of an RF signal for a desired station becomes 10.7 MHz. To accomplish this, the received frequency of the desired station is calculated at the controller
7
on the basis of the local oscillation control signal “a” (Si). On the other hand, a memory
8
stores characteristics of a diode
2
a
. The tuning frequency of the RF tuning circuit
2
is determined by a coil L and the varicap diode
2
a
. Since the coil L is fixed, the tuning frequency varies according to the capacitance of the diode
2
a
. Furthermore, since the capacitance of the diode
2
a
changes with a tuning correction signal “b”, the tuning frequency changes according to the tuning correction signal “b”. As a result, the tuning correction signal “b” increases as the tuning frequency rises as shown by a broken line in FIG.
3
. The memory
8
stores characteristic resulting data which is discrete and has narrower data intervals as the frequency rises, as shown by the circles in FIG.
3
. Since the received frequency of the desired station calculated in step S
1
is to become the tuning frequency, the controller
7
determines which region of the tuning frequency contains the received frequency of the desired station (S
2
). For example, if the received frequency of the desired station is between the tuning frequencies of A and B, a formula for a straight line connecting the corresponding data A and B is determined (S
3
), and the tuning correction signal “b” for the desired station is calculated by substituting the received frequency of the desired station into the straight line formula (S
4
). If the received frequency is not between A and B, a straight line formula is determined from data of both ends of that region (S
5
). The calculated tuning correction signal “b” is impressed onto the diode
2
a
, the capacitance of the diode
2
a
is set, and the tuning frequency of the RF tuning circuit
2
is tuned to the frequency of the desired station (S
6
). In this manner, the tuning frequency of the RF tuning circuit
2
matches the frequency of the desired station so that tracking error is prevented.
However, the coil L and the varicap diode
2
a
have positive temperature characteristics. Thus, as the temperature changes within the radio receiver, the capacitance of the diode
2
a
changes. Since the tuning frequency of the RF tuning circuit
2
is corrected by the fixed tuning correction signal “b”, the tuning frequency of the RF tuning circuit
2
changes from the change in temperature.
SUMMARY OF THE INVENTION
In known radio receivers, when the temperature in the radio receiver changes due to heat dissipation of the radio receiver or to a change in the outside air temperature, a problem occurs where the tuning frequency deviates from the frequency of the desired station to result in tracking error, even if the RF tuning frequency is corrected beforehand to the received frequency of the desired station. It is an object of the present invention to solve this problem.
The present invention comprises, in a radio receiver having an RF tuning circuit for tuning an RF signal and a correction circuit for generating a correction signal to correct a tuning frequency of the RF tuning circuit so as to match a frequency of a desired station, a temperature detecting means for detecting a temperature of the radio receiver and an adjusting means for fine adjusting the correction signal in accordance with the temperature.
The adjusting means has a first reference temperature and a second reference temperature, which is higher than the first reference temperature, and is characterized by fine adjusting the above-mentioned correction signal only by a first predetermined amount when the above-mentioned temperature is lower than the first reference temperature, by fine adjusting the above-mentioned correction signal by only a second predetermined amount when the above-mentioned temperature is higher than the second reference temperature, and by not fine adjusting the above-mentioned correction signal when the above-mentioned temperature is higher than or equal to the first reference temperature and lower than or equal to the second reference temperature.
Furthermore, the adjusting means is characterized by slowing the fine adjustment speed when fine adjusting the correction signal.
Still further, the adjusting means is characterized by determining which of a plurality of regions contains the detected temperature, and by correcting the above-mentioned correction signal by an adjustment amount that has been set to match the determined region.
According to the present invention, by fine adjusting the correction signal in accordance with the radio receiver's temperature that is detected by the temperature detecting means and fine adjusting the tuning frequency of the RF tuning circuit, the tuning frequency is fine adjusted so as not to deviate from the received frequency of the desired station due to temperature changes.


REFERENCES:
patent: 3697885 (1972-10-01), Avins et al.
patent: 4528698 (1985-07-01), Fraser
patent: 4921467 (1990-05-01), Lax
patent: 5428829 (1995-06-01), Osburn et al.
patent: 5634205 (1997-05-01), Kurisu et al.
patent: 5740525 (1998-04-01), Spears
patent: 5774800 (1998-06-01), Mori
patent: 5991609 (1999-11-01), Marrah et al.

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