Pulse or digital communications – Receivers
Reexamination Certificate
1999-05-21
2003-01-28
Corrielus, Jean (Department: 2631)
Pulse or digital communications
Receivers
C375S373000, C331S00100A, C331S056000, C455S130000, C455S260000
Reexamination Certificate
active
06512801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to receivers, and more specifically to a receiver for down-converting an inputted signal via an antenna and then demodulating the converted signal.
2. Description of the Background Art
Conventionally, in some cases, a receiver down-converts a signal S inputted from outside to a signal with an intermediate frequency band (hereinafter referred to as IF band). Down-conversion can be realized by mixing the inputted signal S (frequency f
S
) with a local oscillation output V
O
(frequency f
O
) in a mixer inside the receiver.
The local oscillation output V
O
is conventionally generated by a voltage controlled oscillator (hereinafter referred to as VCO) having a circuitry constitution as shown in FIG.
11
. The VCO of
FIG. 11
is structured of discrete components, comprising a surface acoustic wave (SAW) resonator
111
, a variable capacitance diode
112
and other components. Note that
FIG. 11
also shows an equivalent circuit of the SAW resonator
111
. The variable capacitance diode
112
is connected in parallel to the SAW resonator
111
. With the capacity of the variable capacitance diode
112
adjusted and further with a predetermined control voltage V
C
applied to the VCO, the VCO generates the local oscillation output V
O
having variable frequency.
The SAW resonator
111
is expensive and large in size, and its peripheral circuits are structured of discrete components. It is therefore difficult to downsize the VCO and construct it at low cost, and furthermore know-how for mounting these components is required. Against such background, the VCO has come to be constituted on an integrated circuit.
FIG. 12
shows a circuit diagram of a VCO constituted on an integrated circuit. As compared with the VCO of
FIG. 11
, the VCO of
FIG. 12
is different in that it takes an integrated circuit form and that an LC oscillator
121
is substituted for the SAW resonator
111
.
Assume that a large number of ICs including the VCOs of
FIG. 12
are manufactured under certain conditions. For each of the VCOs, a characteristic of the frequency f
O
of the local oscillation output V
O
with respect to the control voltage V
C
(hereinafter referred to as f
O
vs. V
C
characteristic) is measured. The f
O
vs. V
C
characteristic curve has a linear region and a saturation region. Furthermore, the f
O
vs. V
C
characteristic curves disperse with a constant deviation from a design target of the VCOs (refer to a double-headed arrow in FIG.
13
). Such dispersion is hereinafter referred to as manufacturing dispersion. Due to this manufacturing dispersion, the saturation region of the f
O
vs. V
C
characteristic curve is within a receive band B in some cases. As a result, the receiver cannot down-convert the inputted signal S correctly. It is therefore ideal that each VCO manufactured under the same conditions does not have manufacturing dispersion, which is however difficult in reality. The receive band B is a frequency band which the receiver including the VCOs has to receive and also with which the above signal S is sent out.
For this reason, the following method has been considered. A plurality of VCOs with different f
O
vs. V
C
characteristic curves from each other are integrated in an IC. When the control voltage V
C
of the same level is applied, the plurality of VCOs generate the local oscillation output V
O
with a different frequency f
O
, respectively. A VCO control portion is placed on the periphery of each of such VCOs. The VCO control portion has to select one VCO whose f
O
vs. V
C
characteristic curve reliably covers the receive band B from among the plurality of VCOs. Further, this selecting processing is preferably carried out at high speed.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a receiver for selecting an appropriate VCO at high speed. This object is achieved by the following aspects. Further, each aspect has unique technical effects as described below.
A first aspect of the present invention is directed to a receiver for subjecting an inputted signal via an antenna to down-conversion and then demodulating the converted signal, comprising:
a plurality of voltage controlled oscillators (hereinafter referred to as VCOs), each provided with a common control voltage and generating a local oscillation output having a different frequency according to the control voltage;
a PLL circuit for generating the control voltage based on the local oscillation output fed back from each of the VCOs and a reference signal having a reference frequency;
a mixer for mixing frequencies of the inputted signal via the antenna and the local oscillation output from each of the VCOs, and performing the down-conversion; and
a VCO control portion for testing each of the VCOs in a test mode to be executed in advance, and controlling switching of the VCOs in a receive mode of receiving the inputted signal via the antenna;
in the test mode, the VCO control portion
detecting whether the PLL circuit locks using the local oscillation output from each of the VCOs or not as sequentially switching and activating the VCOs, and determining one appropriate VCO based on a detected result;
in the receive mode, the VCO control portion
selectively activating the VCO determined in the test mode, and providing a local oscillation output of the VCO f or the mixer.
In the first aspect, in the test mode, the appropriate VCO is selected for use in the receive mode. In this test mode, the VCO control portion sequentially switches and activates the VCOs to determine an optimal VCO based on the detected result as to whether the PLL circuit locks using the local oscillation output from each VCO. Therefore, in the receive mode, the mixer performs down-conversion using the local oscillation output from the VCO with which the PLL circuit reliably locks. This allows the receiver according to the first aspect to select an appropriate VCO for the above down-conversion.
According to a second aspect, in the first aspect, the VCO control portion holds the detected result in a first table as pattern data, refers to a second table into which the appropriate VCO for each assumed pattern is written, and determines the appropriate VCO corresponding to the pattern data held in the first table.
In the second aspect, the VCO control portion determines the optimal VCO corresponding to the pattern data stored in the first table referring to the second table. Previously written into the second table are assumed patterns and their corresponding optimal VCOs. This allows the receiver according to the second aspect to select the optimal VCO corresponding to the detected result.
According to a third aspect, in the first aspect, the second table is configured based on manufacturing dispersion of the VCOs.
In accordance with the third aspect, the second table is configured based on the above manufacturing dispersion. This allows the receiver according to the third aspect to select the optimal VCO irrespective of manufacturing dispersion of the VCOs.
According to a fourth aspect, in the first aspect, the PLL circuit includes a programmable divider for dividing the fed-back local oscillation output using a predetermined dividing ratio set by the VCO control portion, and generates a control voltage based on a local oscillation output divided by the programmable divider and the reference signal; and
in the test mode, the VCO control portion sets a reference dividing ratio with which each of the VCOs can generate a local oscillation output having a frequency within a band in which the inputted signal is included as the predetermined dividing ratio.
In accordance with the fourth aspect, since the reference dividing ratio as described above is set in the programmable divider, it is possible to let the PLL circuit lock according to the inputted signal.
According to a fifth aspect, in the fourth aspect, the reference dividing ratio is a dividing ratio with which each of the VCOs can generate a local oscillation output having a cent
Corrielus Jean
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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