Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Phase comparison
Reexamination Certificate
2002-03-04
2004-05-04
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Phase comparison
C324S076390, C324S076770, C331S025000, C331S00100A, C375S295000
Reexamination Certificate
active
06731101
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique useful for the reduction of frequency deviation of the voltage-controlled oscillator (VCO) circuit of LC oscillation type, and particularly to a technique useful for the control of the VCO circuit included in the sending system of a radio communication apparatus which adopt the frequency hopping scheme for example.
In the present situation of crowded radio signals of various communication schemes across the sky brought about by the advanced radio communication technology, the normality of data transmission might be jeopardized due to the interference among signals and the fading. For coping with this matter, there is known a radio communication system which changes the carrier frequency of a signal thereby to prevent the crosstalk with other signals of adjacent frequency bands. For example, a protocol called Bluetooth, which standardizes the wireless data transmission for personal computers and their peripheral units such as printers, adopts the spread spectrum scheme based on frequency hopping of 1-MHz step in the frequency band of 2.4-2.48 GHz (2.4 GHz band) as shown in
FIG. 9
, thereby preventing the crosstalk of signals of adjacent frequency bands. The Bluetooth protocol also adopts the frequency modulation scheme which renders the modulation of ±160 kHz to the carrier signal for data transmission.
In this frequency modulation, it is conceivable to control the frequency by controlling the VCO circuit directly by the transmission data. There is known a VCO circuit which controls the oscillation frequency by varying the current with a control voltage, and also known a VCO circuit of LC oscillation type which varies the oscillation frequency by varying the capacitance of a variable capacitor with a control voltage.
SUMMARY OF THE INVENTION
In the case of frequency modulation by data of transmission based on frequency hopping, frequency hopping control is needed for the carrier signal in addition to the frequency modulation by the data, and accordingly two control systems are necessary.
The inventors of the present invention have studied the use of an LC-oscillation VCO circuit which includes varactor diodes as shown in
FIG. 2
in developing a radio communication LSI (large-scale semiconductor integrated circuit) device which adopts the above-mentioned radio communication scheme.
The study has revealed that the adoption of frequency modulation based on direct control of LC-oscillation VCO is problematic in that the switching of carrier frequency causes the frequency deviation to arise. The Bluetooth protocol recommends a modulation range of ±140-175 kHz for the transmission of a signal having its 2.4-GHz carrier signal rendered the ±160-kHz modulation. Namely, it allows a margin of 35 kHz.
According to the study of the above-mentioned LC-oscillation VCO by the present inventors, when it is attempted to modulate the carrier signal at a constant level in accordance with transmission data, i.e., when it is attempted to control the oscillation frequency of the VCO shown in
FIG. 2
at a constant level of control voltage Vcnt
2
irrespective of the carrier frequency, switching of frequency by another control voltage Vcnt
1
of frequency hopping causes the variation of not only the capacitance of one varactor diode pair Dv
11
and Dv
12
, but also the total capacitance of another varactor diode pair Dv
21
and Dv
22
.
The LC-oscillation VCO has its oscillation frequency f
osc
evaluated as follows.
f
OSC
=
1
2
π
LC
(
1
)
The rate of frequency variation in response to the variation of capacitance C (i.e., df
osc
/dC) is formulated as follows.
ⅆ
f
OSC
ⅆ
C
=
1
2
π
L
·
(
-
1
2
)
·
(
1
C
)
3
=
1
2
π
LC
·
(
-
1
2
)
·
(
1
C
)
=
(
-
1
2
)
·
f
OSC
C
=
(
-
1
2
)
·
f
OSC
·
(
2
π
f
OSC
)
2
·
L
=
-
2
π
2
·
f
OSC
3
·
L
(
2
)
Accordingly, the rate of frequency variation in response to the variation of capacitance C (df
osc
/dC) is proportional to the third power of f
osc
. It was revealed that the frequency variation caused by the variation of the above-mentioned total capacitance resulting from the control of hopping carrier frequency varies the modulation gain of VCO, causing the modulation frequency to deviate with the carrier frequency as shown in
FIG. 7A. A
presumed reason for this affair is open-loop control of the oscillation frequency for modulation against closed-loop control of the oscillation frequency for frequency hopping.
The modulation frequency deviation is maximum when the VCO oscillation frequency f
osc
hops from 2.402 GHz to 2.480 GHz. The variation of modulation gain for f1=2.402 GHz and f2=2.480 GHz is evaluated as follows.
Modulation gain at high-limit frequency/Modulation gain at
high
-
limit
frequency
low
-
limit
frequency
=
(
f
2
f
1
)
3
=
(
2.48
GHz
2.402
GHz
)
3
≈
1.1
(
3
)
Specifically, the modulation gain has a 10% variation between the high-limit and low-limit of the VCO oscillation frequency as shown in FIG.
7
A. This graph is plotted to present the modulation frequency deviation in terms of the ratio which is based on the frequency deviation of “1” at a carrier frequency of 2.44 GHz, i.e., the control voltage Vcnt
2
is set such that the modulation frequency is intended 160 kHz when the carrier frequency is 2.44 GHz. Therefore, the 10% variation is equivalent to 16 kHz.
On this account, frequencies as much as 16 kHz out of the 35-kHz frequency margin is lost due to frequency hopping, leaving a practical frequency margin of 20 kHz or less. When the variations of temperature and power voltage are considered, the frequency margin further decreases, and it becomes extremely difficult to design a sending system circuit having optimal characteristics.
The present invention is intended to solve the above-mentioned prior art problem, and its prime object is to reduce the frequency deviation of the LC-oscillation VCO circuit and of the VCO in the modulation semiconductor integrated circuit device used in a radio communication apparatus of frequency hopping type.
Another object of this invention is to provide a modulation semiconductor integrated circuit device useful for building a radio communication apparatus which is immune to crosstalk and performs accurate data transmission.
Among the affairs of the present invention disclosed in this specification, representatives are briefed as follows.
The inventive modulation semiconductor integrated circuit device controls a voltage-controlled oscillation circuit with a first control voltage to produce a base frequency signal, controls at the same time the voltage-controlled oscillation circuit with a second control voltage which is based on data to be transmitted thereby to implement the frequency modulation, and transmits the data signal while changing the base frequency, wherein the integrated circuit device controls the base current value of a circuit which generates the second control voltage in response to the change of the base frequency such that the variation of the second control voltage of the voltage-controlled oscillation circuit has a characteristic opposite to the characteristic of modulation frequency deviation of the voltage-controlled oscillation circuit.
More specifically, the inventive modulation semiconductor integrated circuit device produces a carrier frequency signal with an LC-oscillation VCO, controls at the same time the LC-oscillation VCO based on data to be transmitted thereby to implement the frequency modulation, and transmits the data signal while changing the carrier frequency, wherein the integrated circuit device varies the base current value of a circuit (e.g., D/A conversion circuit) which produces a control voltage of the VCO in response to the change of the carrier frequency such that the variation of the
Kokubo Masaru
Matsuura Tatsuji
Miyagawa Hirokazu
Yamamoto Katsumi
Le N.
Mattingly Stanger & Malur, P.C.
Nguyen Vincent Q.
Renasas Technology Corp.
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