JP2002223169A - Wireless unit and oscillated frequency correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless unit the center frequency of an oscillator of which is stabilized that can cope with even the case of modulation by an optional frequency modulation width without the need for adopting an entirely complicated circuit configuration. SOLUTION: A resonator 4 with a high frequency stability is coupled to a line through which an oscillation signal from an oscillator VCO 1 is transmitted and a control voltage and control data at which a transmission signal level of the resonator 4 reaches a peak are detected from the transmission signal level of the resonator 4 when the control voltage with respect to the VCO 1 is changed and the oscillation signal of the VCO 1 is frequency-modulated on the basis of the frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio apparatus provided with an oscillator for generating a frequency signal in an ultrahigh frequency band such as a microwave band or a millimeter wave band, and a method for correcting an oscillation frequency.

[0002]

2. Description of the Related Art Generally, a circuit for outputting a frequency modulation signal in accordance with an input signal is provided with a voltage-controlled oscillator. Particularly in an ultra-high frequency band, stability of the oscillation center frequency is required.

A general method for stabilizing the frequency of an oscillator is to keep the temperature of the oscillator constant in a thermostat.
A resonator such as a dielectric resonator having excellent resonance frequency temperature characteristics is incorporated in the oscillation circuit. The oscillation frequency is controlled by PLL control. There was a method.

[0004]

However, in the above method, since only the control of the temperature change is performed, there is no effect on the load change. It has no effect on the drift of the oscillation frequency of the oscillator itself. The size is increased due to the necessity of a heat insulating cover. Large power consumption for constant temperature occurs. There are drawbacks such as. In the method, the oscillation frequency also changes with factors other than the characteristics of the resonator. That is, since the oscillation circuit is configured by a combination with the active element, advanced control is required, and the entire circuit is complicated. A dielectric resonator having an excellent temperature characteristic of the resonance frequency has a high Q, so that it is difficult to perform FM modulation over a wide band. There is a disadvantage that. Further, the method has a drawback that a circuit for down-conversion until it is compared with a reference signal becomes complicated and expensive, especially in a millimeter wave band.

On the other hand, Japanese Patent Application Laid-Open No. H10-163756 discloses an apparatus in which the voltage of an input signal is controlled in consideration of the frequency characteristics of a voltage controlled oscillator (VCO). In this method, a triangular wave is given as a control voltage signal to the VCO, and the center frequency is stabilized by controlling the offset of the triangular wave according to the difference between the lowest oscillation frequency and the highest oscillation frequency.

However, a circuit portion after the resonator coupled to the VCO requires a sample-and-hold circuit, a comparison circuit, and a loop filter, and also requires a number of circuits such as a differentiation circuit and an edge detection circuit. Further, the relationship between the Q (frequency bandwidth) of the resonator and the FM modulation width is very large, and the QL characteristics of the resonator must be determined according to the FM modulation width of the VCO and the sensitivity of the detector. Therefore, when performing narrow-band FM modulation, a resonator having a high Q is required, which makes manufacturing difficult and increases the size. Therefore, FM modulation cannot be performed over a wide range and with an arbitrary modulation width. Furthermore, there are various problems that the modulation signal must be a triangular wave and cannot be used for communication other than, for example, FM-CW radar.

An object of the present invention is to solve the above-mentioned various problems and stabilize the center frequency of an oscillator which can cope with a case where modulation is performed at an arbitrary frequency modulation width without taking a complicated circuit configuration as a whole. And a method of correcting an oscillation frequency.

[0008]

A wireless device according to the present invention comprises:
A resonator coupled to a line for transmitting an oscillation signal of a voltage-controllable oscillator; a level detection unit coupled to the resonator to detect a transmission signal level of the resonator; and changing a frequency control voltage of the oscillator. And a peak detecting means for obtaining a frequency control voltage at which the transmitted signal level of the resonator is maximized by the level detecting means, and a frequency control voltage at which the transmitted signal level is maximized as a reference. Modulating means for modulating the frequency control voltage with the transmission signal.

As described above, based on the transmission signal level of the resonator coupled to the transmission line for transmitting the oscillation signal, the frequency control voltage that maximizes the transmission signal level is obtained, so that the oscillator can be operated at the resonance frequency of the resonator. The frequency control voltage required for oscillation is determined. By modulating the frequency control voltage with a transmission signal with reference to a frequency control voltage required to oscillate the oscillator at the resonance frequency of the resonator (for example, as a center frequency), the oscillation center frequency is stabilized.

Further, the radio apparatus according to the present invention sweeps the oscillation frequency by gradually changing the frequency control voltage of the oscillator,
A frequency control voltage at which the transmitted signal level gradually changing with the sweep of the oscillation frequency becomes the maximum is obtained as a frequency control voltage required to oscillate the oscillator at the resonance frequency of the resonator. As a result, peak detection is performed by simple arithmetic processing or a simple circuit configuration.

Further, the radio apparatus of the present invention changes the oscillation frequency by changing the frequency control voltage of the oscillator in a plurality of steps, obtains a function of the transmission signal level with respect to the frequency control voltage, and obtains the transmission signal level based on the function. The frequency control voltage required to maximize the signal level is determined. Thus, the number of switching steps of the frequency control voltage is reduced, and peak detection is accurately performed in a short time.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a wireless device according to an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a block diagram of an FM-CW type radar module. Here, VCO1 is a voltage controlled oscillator,
CPL2 is coupler, CIR9 is circulator, MI
X11 is a mixer. Coupler CPL2 is VCO1
Is transmitted to the input port side of the circulator CIR9, and a part of the signal is extracted as a local signal and supplied to the mixer MIX11. Circulator CI
R9 transmits the transmission signal to the antenna 10 and the antenna 1
The received signal is transmitted from mixer 0 to mixer 11. Coupler 3
Is a coupler for coupling the resonator 4 with the line for transmitting the transmission signal. The detector 5 is coupled to the resonator 4 and detects a transmission signal of the resonator 4. The AD converter 6 converts a signal detected by the detector 5 into digital data. CPU
7 reads the data from the AD converter 6 and outputs the result of the processing described later to the DA converter 8. The DA converter 8 is a DA converter having a low-pass filter for smoothing an output signal. The signal processing circuit 12 performs predetermined signal processing on the output signal of the mixer 11. CP
U7 reads the result.

The CPU 7 changes the oscillation frequency of the VCO 1 into a triangular wave according to the data supplied to the DA converter 8, and outputs a signal based on a combination of two beat signals (downbeat and upbeat) of a reflected signal from the target and a local signal. Calculate the distance to the target and the relative speed.

FIG. 2 shows a specific configuration of the coupler 3, the resonator 4, and the detector 5. Where 31 is
This is a dielectric strip constituting a dielectric line which is a transmission line from the coupler 2 to the circulator 9 shown in FIG. A dielectric line is constituted by the dielectric strip 31 and upper and lower conductive planes sandwiching the dielectric strip 31.
In FIG. 2, the conductor plane is omitted. 4 has excellent temperature characteristics of the resonance frequency, that is, high stability of the resonance frequency.
This is a dielectric resonator made of a cylindrical dielectric material that resonates in the TE01δ mode. Reference numerals 52 and 53 denote line patterns on a substrate arranged between the upper and lower conductor surfaces, and a microstrip line or a suspended line is constituted by the upper and lower conductor planes and the line pattern on the substrate. One end of the line pattern 51 is grounded.
A Schottky barrier diode (SBD) 50 is mounted between the other end of the line pattern 51 and one end of the line pattern 52. Track pattern 5
A stub for trapping an RF signal is provided in the middle of another line pattern 53 extending from the middle of Step 2.

The dielectric line formed by the dielectric strip 31 and the dielectric resonator 4 are coupled by a coupling amount of Qe1, and the dielectric resonator 4 and the lines 51 and 52 are connected by Qe2.
In a binding amount of The signals excited in the lines 51 and 52 are detected by the SBD 50, and the detected signals are
Is supplied to the amplifying circuit 54. The amplifying circuit 54 has a smoothing circuit at its input / output stage, and supplies a voltage signal corresponding to the level of the detection signal to the AD converter 6.

In the example described above, the resonator is coupled to the transmission line between the coupler for extracting the local signal and the circulator, but the resonator is connected to the inside of the VCO 1 in FIG. May be combined. FIG. 3 shows such an example. In this example, F
ET is connected to lines L1, L2, and L3, and a resistor R is provided between the end of L1 and ground. Such a circuit constitutes an FET oscillator. At a predetermined position of the output line L3, a resonator made of a dielectric material having a columnar shape is closely arranged, a resonator is coupled to the line L3, and a line connecting an SBD to this resonator is closely arranged. .

With such a structure, the transmission signal level of the resonator coupled to the output signal of the oscillator can be extracted as a detection output by the SBD.

FIG. 4 is a diagram showing the relationship between the oscillation frequency of VCO 1 shown in FIG. 1 and the input voltage of AD converter 6 (ie, the output voltage of detector 5). As described above, the input voltage of the AD converter draws a substantially Gaussian curve with the change of the oscillation frequency of the VCO 1. This is due to the characteristics of the transmission signal level with respect to the input signal frequency of the resonator 4. That is, when the frequency of the input signal to the resonator is equal to the resonance frequency fo of the resonator, the input voltage of the AD converter becomes maximum, and as the frequency becomes higher and lower therefrom, the input voltage of the AD converter becomes descend. If the frequency range in which the input voltage of the AD converter reaches the read limit level (voltage corresponding to the resolution of AD conversion) is BW, this BW is VCO1
The characteristics of the AD converter 6 are determined in advance so as to be wider than the FM modulation width.

FIG. 5 shows an example of a change in the control voltage for the VCO 1, its oscillation frequency, the resonance characteristics of the resonator 4, and the input voltage to the AD converter. If the control voltage for the VCO 1 is changed in a triangular waveform over time as shown in FIG. 5A, the oscillation frequency of the VCO 1 is changed as shown in FIG. 5B. That is, V
When the control voltage for CO1 is Vc1, the oscillation frequency of VCO1 is f1, and when the control voltage is Vc2, the oscillation frequency is f2.
Thus, the oscillating frequency increases with an increase in the control voltage. The width of change from frequency f1 to f6 is BW shown in FIG.
It is determined so that it falls within the range.

As the oscillation frequency of the VCO changes, the transmission signal level of the resonator 4 also changes in accordance with the resonator characteristics. Therefore, the input voltage of the AD converter is changed as shown in FIG. Change. That is, when the oscillation frequency is f1, the input voltage to the AD converter is V1, when the oscillation frequency is f2, V2, when the oscillation frequency is f3, V3.
V4 at f4, V5 at f5, V6 at f6, and so on.

In this example, the resonance frequency fo of the resonator is f
Therefore, the input voltage V3 to the AD converter at the time 3 when the oscillation frequency of the VCO becomes f3 becomes the maximum value. Therefore, if a control voltage is applied to the VCO 1 so as to perform FM modulation around Vc3, the center frequency of FM modulation can be made to match fo. TE
Since the 01δ mode dielectric resonator 4 has high frequency stability against temperature change, the above fo can be used as a frequency reference. Therefore, even if there is a temperature change, the center frequency of FM modulation can be kept constant.

Next, a method of obtaining a control voltage for causing the VCO to oscillate at the frequency fo will be described with reference to the flowchart of FIG. First, the design center voltage Vo is set to 3 [V], the number of control voltage switching steps Step is 64, and the center value Ncnt of the counter for counting the number of steps is set.
And the initial value of a variable Vmax holding the maximum value for detecting the peak of the input voltage of the AD converter is set to 0.

Next, N as a counter for counting the number of steps is determined as Ncnt- (Step / 2), and data corresponding to the number of steps N (D shown in FIG. 1).
Data given to A converter 8) Vda = Vm = Vm
It is determined by in + Vstep * N. Here, Vstep is determined by Vstep = modulation width / (modulation sensitivity * step). The modulation width is, for example, 120 MHz and the modulation sensitivity is 20 MH
z. Also, Vmin is Vmin = Vo−Vst
It is determined by ep * Step / 2. The oscillation frequency of the VCO 1 is determined by the output of the DA converter 8 determined by this data, and the output value Vad of the AD converter 6 at that time is determined.
(N) is read. The value Vad (N) read this time is
If it is larger than the maximum value Vmax, Vad
(N) is set as a new Vmax, and the number of steps N at that time is held as Ncnt. Also, Vda (N) is changed to Vcn
It is held as t.

Next, N is incremented by one, and the above processing is repeated. If the number of steps N exceeds a predetermined maximum number of steps, Step, V
Output cnt and Ncnt. By changing the data supplied to the DA converter 8 in FIG. 1 in a triangular waveform around the value corresponding to Ncnt, it is possible to perform FM modulation around the resonance frequency fo of the resonator 4.

Next, another method for obtaining a control voltage for setting the oscillation frequency of the VCO to fo will be described with reference to FIGS.

In the procedure shown in FIG. 6, the number of steps of changing the control voltage for the VCO is increased so that the control voltage when the transmission signal level of the resonator reaches a peak is directly detected. If the control voltage at the time when the transmission signal level reaches a peak is calculated, the VCO
Can be reduced in the number of control voltage stages.

FIG. 7 shows an example of a change in the control voltage for the VCO 1, its oscillation frequency, the resonance characteristics of the resonator 4, and the input voltage to the AD converter. As in the example shown in FIG. 5, if the control voltage for the VCO 1 is changed in a triangular waveform over time, as shown in FIG.
Accordingly, the oscillation frequency of VCO1 changes as shown in FIG.

With the change in the oscillation frequency of the VCO, the level of the transmission signal of the resonator 4 changes, and the input voltage of the AD converter changes as shown in FIG.
In this example, since the resonance frequency fo of the resonator is between f3 and f4, the peak of the input voltage of the AD converter exists between times 3 and 4. This peak position is determined by a function of the transmission signal level of the resonator (that is, the output value of the AD converter) with respect to the control voltage applied to the VCO 1.

FIG. 8 is a flowchart showing how to obtain a control voltage for oscillating the VCO at the frequency fo by the above-described method. First, the design center voltage Vo is set to 3
[V], the number of control voltage switching steps is set to 6, and the initial value N of a counter for counting the number of steps is set to 1. Next, data (data given to the DA converter 8 shown in FIG. 1) Vd according to the number of steps N
a is defined by Vda = Vmin + Vstep * N. Here, Vstep and Vmin are determined in the same manner as in the above-described embodiment. The oscillation frequency of the VCO 1 is determined by the output of the DA converter 8 determined by this data, and the output value Vad (N) of the AD converter 6 at that time is read.

The above processing is repeated until N as a counter for counting the number of steps reaches the maximum number of steps Step. When the maximum number of steps is reached, the relationship between the control voltage and the output value of the AD converter is converted into a function, and the coefficient of the function is obtained. For example, assuming that the control voltage is x and the output value of the AD converter is y, y = x / (ax ² + bx + c)
When the transmission signal level of the resonator reaches a peak, the control voltage Xpeek becomes Xpeek = b / (2
a), the output value Ypeek of the AD converter at that time is Ype
ek = determined in ^{(b 2 -4c) / (4a} ). The coefficients a, b, and c of the above function may be obtained by the least square method.

[0032]

According to the present invention, based on the transmission signal level of the resonator coupled to the line for transmitting the oscillation signal, the frequency control voltage at which the transmission signal level becomes maximum is determined, whereby the resonance of the resonator is obtained. Since the frequency control voltage required to cause the oscillator to oscillate at the frequency is determined, the oscillation center frequency can be stabilized by modulating the transmission signal based on the frequency control voltage (for example, as the center frequency). In addition, since the resonance frequency stability with respect to the temperature of the resonator is used, variation in the Q (frequency bandwidth) characteristics of the resonator does not pose a problem. Therefore, F
Regardless of the modulation width of the M modulation, manufacturing is easy and the size is not increased. Therefore, FM modulation can be performed over a wide range and with an arbitrary modulation width. Further, the modulation signal at the time of actual use does not need to be a triangular wave.
It can also be used for communications other than W radar.

Further, according to the present invention, the oscillation frequency is swept by gradually changing the frequency control voltage of the oscillator, and the frequency control voltage at which the transmitted signal level gradually changing along with the sweep of the oscillation frequency becomes the maximum is set as: By obtaining the frequency control voltage required to cause the oscillator to oscillate at the resonance frequency of the resonator, peak detection can be performed with simple arithmetic processing or a simple circuit configuration.

According to the present invention, the oscillation frequency is changed by changing the frequency control voltage of the oscillator in a plurality of steps, and the function of the transmission signal level of the resonator with respect to the frequency control voltage is obtained. By determining the frequency control voltage required to maximize the transmission signal level, peak detection can be performed accurately even with a small number of switching steps of the frequency control voltage, and the frequency control voltage required to oscillate the oscillator at the resonance frequency of the resonator Can be obtained in a short time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an FM-CW type radar module.

FIG. 2 is a block diagram showing a configuration of a coupling portion between a transmission line and a resonator and a detector.

FIG. 3 is a diagram showing another configuration example of a portion to which the resonator is coupled;

FIG. 4 is a diagram showing a relationship between a change in an oscillation frequency of a VCO and a change in an input voltage of an AD converter.

FIG. 5 is a diagram showing an example of the relationship among a control voltage of a VCO and its oscillation frequency, a transmission signal level of a resonator, and an input voltage of an AD converter.

FIG. 6 is a flowchart showing a procedure for obtaining a control voltage and control data required to oscillate at a frequency fo.

FIG. 7 is a diagram showing another example of the relationship between a control voltage of a VCO, its oscillation frequency, a transmission signal level of a resonator, and an input voltage of an AD converter.

FIG. 8 is a flowchart showing another procedure for obtaining a control voltage and control data required to oscillate at a frequency fo.

[Explanation of symbols]

 1-Voltage Controlled Oscillator (VCO) 2-Coupler 6-AD Converter 8-DA Converter 9-Circulator 10-Antenna 11-Mixer 31-Dielectric Strip 50-Schottky Barrier Diode (SBD) 51,52,53-Line Pattern

Claims (4)

[Claims] 1. A wireless device having a voltage-controllable oscillator, wherein: a resonator coupled to a line for transmitting an oscillation signal of the oscillator; and a resonator coupled to the resonator to detect a transmission signal level of the resonator. A level detecting unit, a peak detecting unit that changes an oscillation frequency by changing a frequency control voltage of the oscillator, and obtains a frequency control voltage that maximizes a transmission signal level of the resonator by the level detecting unit; A modulating means for modulating the frequency control voltage with a transmission signal based on a frequency control voltage having a maximum signal level. 2. The wireless device according to claim 1, wherein said peak detecting means sweeps an oscillation frequency by gradually changing a frequency control voltage of said oscillator, and obtains a frequency control voltage at which said transmitted signal level is maximized. . 3. The peak detecting means changes an oscillation frequency by changing a frequency control voltage of the oscillator in a plurality of steps, obtains a function of a transmission signal level with respect to the frequency control voltage, and calculates the transmission signal level from the function. The wireless device according to claim 1, wherein a frequency control voltage that maximizes a frequency control voltage is obtained. 4. A resonator which is coupled to a line for transmitting an oscillation signal of a voltage-controllable oscillator, changes an oscillation frequency by changing a frequency control voltage of the oscillator, and has a maximum transmission signal level of the resonator. An oscillation frequency correction method for determining a frequency control voltage to be used and controlling the oscillation frequency based on the frequency control voltage.