Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
2000-11-14
2004-03-30
Nguyen, Duc M. (Department: 2685)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S193100, C455S193200
Reexamination Certificate
active
06714771
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to broadcast radio signal receiving systems, and more specifically to such systems including a seek function operable to sequentially search a band of radio frequencies for broadcast signals above a predefined signal strength.
BACKGROUND OF THE INVENTION
Electronic circuits for controlling operation of a broadcast radio receiver are known and have been widely implemented in both home and automotive entertainment systems. One such electronic circuit provides a so-called “seek” function operable to sequentially (i.e., either incrementally or decrementally) search a band of radio frequencies for broadcast signals above a predefined signal strength. Typically, such a circuit is responsive to operator selection of the seek function to search either forward or backward from the currently selected broadcast frequency, to identify as an available broadcast station the first broadcast frequency detected as having a signal strength greater than a predefined signal strength, and to tune the radio receiver to the identified broadcast frequency.
Referring to
FIG. 1
, an example of one known radio frequency receiver
10
is shown having an antenna
12
electronically connected to a tuning circuit
14
via signal path
16
. An output of the tuning circuit
12
is connected to an input of a seek circuit
18
via signal path
22
, wherein tuning circuit
14
provides an analog radio signal on signal path
22
having a magnitude corresponding to the signal strength of the currently tuned frequency. In this known embodiment, the seek circuit
18
is an analog circuit and includes (among other elements and functions) a comparator circuit
20
having a non-inverting input connected to signal path
22
, an inverting input connected to an analog reference voltage VREF, and an output that is fed back to the tuning circuit
14
via signal path
24
. A SEEK selector
26
is typically provided on the face plate (not shown) of RF receiver
10
and is electrically connected to seek circuit
18
via signal path
28
. The tuning circuit
14
includes another output connected to an audio amplifier circuit (not shown) of RF receiver
10
via signal path
30
as is known in the art.
In normal operation of RF receiver
10
, the tuning circuit
14
is operable to tune to a selected frequency, and to provide a corresponding radio signal to the amplifier circuit for audible reproduction of the signal content. During seek operation, in response to operator depression of the SEEK selector
26
, seek circuit
18
provides a start signal to tuning circuit
14
via signal path
32
. The tuning circuit
14
is responsive to the start signal on signal path
32
to modify, e.g., by either incrementing or decrementing, its tuning frequency and provide a radio signal corresponding thereto to comparator
20
on signal path
22
. Comparator
20
is operable to compare the magnitude of the incoming analog radio frequency signal on signal path
22
with the predefined analog reference voltage VREF. As long as the magnitude of the analog radio frequency is less than VREF, the tuning circuit
14
continues to periodically increment or decrement its tuning frequency and pass an analog radio signal corresponding thereto to seek circuit
18
. If, however, the magnitude of the analog radio frequency on signal path
22
is greater than VREF, the comparator
20
changes state and provides a stop signal to tuning circuit
14
via signal path
24
. The tuning circuit
14
is responsive to the stop signal on signal path
24
to halt the seek process and allow reception by RF receiver
10
of radio signals corresponding to the current tuning frequency. In general, the magnitude of the analog reference voltage VREF in the system of
FIG. 1
is typically set at a voltage level above which detected broadcast signals exhibit an acceptable reception quality.
While analog seek circuits of the type illustrated and described with respect to
FIG. 1
have been widely used with a number of different antenna configurations (e.g., front mast, rear mast and active backlite antenna systems), they have been found to exhibit certain drawbacks associated therewith. For example, some antenna systems, such as a passive backlite antenna of the type described in co-pending U.S. Pat. No. 6,031,500, which is assigned to the assignee of the present invention and the contents of which are incorporated herein by reference, exhibit significantly lower RF signal gains than conventional antenna systems. While the lower signal gains of such antenna systems generally do not affect the signal-to-noise ratios of the incoming radio frequency signals, they will result in reduced RF signal strengths provided to tuning circuit
14
, and accordingly reduced magnitude radio signals provided to seek circuit
18
. The quality of reception is mainly dependent upon the signal-to-noise ratio of the received signals and is therefore not affected by lower antenna gains. However, the seek function is dependent only upon the magnitude of the radio signals provided thereto on signal path
22
, and therefore is directly affected by the RF signal gain capability of antenna
12
. Thus, while lower RF gain antenna systems may have similar quality of reception characteristics across a broadcast frequency band, conventional seek circuitry in receivers utilizing such antennas will typically not detect as many broadcast stations as in receivers utilizing higher RF gain antennas.
One solution to the foregoing drawback associated with low antenna gain RF signal receiving systems is to lower the seek level threshold; i.e., lower the analog reference voltage level VREF. However, while this technique increases the seek count for low RF gain antenna systems, it allows the tuning in of broadcast signals having lower than desired reception quality in systems having higher gain antenna systems. Difficulty accordingly arises when interchanging antenna systems between low and high RF gain antennas. Moreover, circuit changes required to establish different VREF levels for different antenna gains are expensive and difficult to track in a production environment. What is therefore needed is an improved seek threshold strategy that is adaptable to a wide range of antenna RF signal gains and is easily modified in a production environment.
SUMMARY OF THE INVENTION
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a radio frequency receiver including a signal seek function comprises a tuning circuit operable in a seek mode to receive and provide radio signals sequentially changing in frequency, means for producing digital signal values corresponding to magnitudes of the radio signals, means for producing a digital reference value corresponding to a reference signal magnitude, and means for producing a stop signal upon detection of a first one of the digital signal values exceeding the digital reference value, wherein the tuning circuit is responsive to the stop signal to halt the seek mode and maintain tuning thereof to a radio signal corresponding to the first one of the digital signal values.
In accordance with another aspect of the present invention, a method of seeking radio frequency signals comprises the steps of conducting a seek process by receiving radio signals sequentially changing in frequency, providing magnitudes of received ones of the radio signals as digital signal values, comparing each of the digital signal values with a digital reference value, and halting the seek process upon detection of a first one of the digital signal values exceeding the digital reference value and allowing reception of radio signals corresponding to the first one of the digital signal values.
One object of the present invention is to provide an improved radio signal seek strategy that is adaptable to a wide range of antenna RF signal gains.
Another object of the present invention is to provide an improved seek threshold circuit that accomplishes these and other objectives.
T
Graham Janalee Ann
Kaczor Anthony E
Martin Douglas Courtney
Nagy Louis Leonard
Chmielewski Stefan V.
Delphi Technologies Inc.
Nguyen Duc M.
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