JP2010139391A - Active antenna and gps unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active antenna that does not require individual gain adjustment work or design. <P>SOLUTION: The active antenna having a variable gain amplification means for changing the gain of a reception signal includes: a supply voltage detection means for detecting a supply voltage that is supplied from equipment at a later stage connected to the active antenna and that changes according to signal quality of a reception signal inputted to the equipment; and a gain control means for controlling the gain of the variable gain means, based on the supply voltage detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an active antenna having variable gain amplification means for changing the gain of a received signal and a GPS (Global Positioning System) unit including the active antenna.

  GPS is a positioning system for measuring position information and the like of an object using GPS signals transmitted from GPS satellites orbiting the earth, and is widely used in daily life.

  In GPS, a plurality of GPS satellites share the same frequency band and transmit a GPS signal by a CDMA (Code Division Multiple Access) method. Specifically, the GPS signal is expressed by 1575 by a navigation message as a communication signal including clock information and orbit information of GPS satellites, and a PRN code (Pseudo Random Noise code) as a spreading code determined for each GPS satellite. .42 MHz carrier obtained by BPSK (Binary Phase Shift Keying) modulation. The GPS receiver selects more than the number of GPS satellites required in principle, receives it by the GPS antenna, generates a PRN code corresponding to the received GPS satellite, and converts the phase of the generated PRN code into a GPS signal. The navigation data is demodulated by multiplying in synchronization. The GPS receiver performs calculation using the navigation data obtained in this way, and generates position information, direction information, moving speed information, and the like of the object.

For the GPS antenna connected to the GPS receiver, for example, an active antenna having a signal amplifier at the subsequent stage of the antenna element is used. The active antenna has a signal level at the signal input terminal of the GPS receiver considering that the GPS signal radiated from the GPS satellite is weak, the gain of the antenna element is small, and there is a transmission loss to the GPS receiver. Is used for the purpose of keeping the above a certain value. An example of a GPS receiver on which such an active antenna is mounted is disclosed in Patent Document 1.
JP 2003-240833 A

  Here, for example, consider a case where the GPS receiver is an in-vehicle GPS receiver mounted on a vehicle or the like. In this case, the length of the cable that electrically connects the GPS receiver and the GPS antenna differs depending on various conditions such as the shape and size of the vehicle body, the GPS receiver, and the GPS antenna mounting position. The signal transmitted from the GPS antenna to the GPS receiver has a high-frequency signal loss that increases in proportion to the cable length. In a state where the total gain of the active antenna including the loss of the high-frequency signal in the cable is insufficient, there is a problem that the GPS signal reception C / N deteriorates and the positioning sensitivity of the GPS receiver deteriorates. Therefore, each time the cable length is different, individual gain adjustment work and design for the signal amplifier of the active antenna is required. However, such individual gain adjustment work and design are undesirable because they increase development cost and lead time.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an active antenna that does not require individual gain adjustment work and design, and a GPS unit including the active antenna. is there.

  An active antenna according to an embodiment of the present invention that solves the above problem is an antenna having variable gain amplification means for changing the gain of a received signal, and has the following characteristics. That is, the active antenna includes power supply voltage detection means for detecting a power supply voltage that is supplied from a subsequent device connected to the active antenna and that changes in accordance with the signal quality of a received signal input to the device, and a detection And gain control means for controlling the gain of the variable gain means based on the supplied power supply voltage.

  According to such a configuration, the gain of the variable gain amplifying means is automatically controlled, so that it is not necessary to perform gain adjustment work and design in consideration of use conditions such as cable length. As a result, the development cost and lead time of the active antenna can be reduced.

  In addition, a GPS unit according to an embodiment of the present invention that solves the above problems is the active antenna described above and a GPS receiver connected to the active antenna, and is a received signal input from the active antenna. Reception quality detection means for detecting the reception quality of the GPS signal, power supply voltage generation means for generating a power supply voltage corresponding to the detected reception quality, and power supply voltage supply means for supplying the generated power supply voltage to the active antenna And a GPS receiver provided.

  According to another aspect, a GPS unit according to the present invention includes the active antenna described above and a GPS receiver connected to the active antenna, and receiving a GPS signal that is a received signal input from the active antenna. Reception quality detection means for detecting quality, superimposed voltage generation means for generating a superimposed voltage obtained by superimposing a voltage corresponding to the detected reception quality on the power supply voltage to be supplied to the active antenna, and the generated superimposed voltage And a GPS receiver including power supply voltage supply means for supplying power to the active antenna as a power supply voltage.

  Here, the GPS receiver has, for example, a configuration having a plurality of reception channels for receiving GPS signals of the respective GPS satellites. At this time, the reception quality detection means is configured to detect an average value of reception qualities of a predetermined number of GPS signals having good reception quality among GPS signals received by each reception channel.

  The GPS unit according to the present invention is an in-vehicle GPS unit mounted on a moving body such as a vehicle.

  According to the active antenna and the GPS unit of the present invention, since the gain of the variable gain amplifying means of the active antenna is automatically controlled, gain adjustment work and design considering the use conditions such as the cable length are not required. As a result, the development cost and lead time of the active antenna can be reduced.

  Hereinafter, the configuration and operation of a GPS unit according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of the GPS unit 100 of the present embodiment. As shown in FIG. 1, the GPS unit 100 includes an active antenna 1 and a GPS receiver module 3. The active antenna 1 and the GPS receiver module 3 are electrically connected by an RF (Radio Frequency) cable 2. The GPS unit 100 is mounted on various application devices such as a carna navigation device, a PND (Personal Navigation Device) that is a simple navigation device, and a mobile phone terminal.

  The PS signal radiated from the GPS satellite is received by the antenna element 11 included in the active antenna 1. The GPS signal received by the antenna element 11 is amplified to a desired signal level by a variable gain LNA (Low Noise Amplifier) 12. The amplified GPS signal is input to a BPF (Band Pass Filter) 13 to remove noise outside the GPS band, and input to the variable gain LNA 14. The GPS signal is amplified again by the variable gain LNA 14 to increase the gain, and is increased to a required signal level by the GPS receiver module 3. The gain control of the variable gain LNAs 12 and 14 is performed by a voltage control circuit 15 that is a power supply unit of the active antenna 1. A detailed description of gain control by the voltage control circuit 15 will be given later.

  The GPS signal output from the variable gain LNA 14 is input to the RF analog processing unit 32 included in the GPS receiver module 3 via the RF cable 2. The GPS signal input to the RF analog processing unit 32 is an intermediate signal suitable for signal processing such as filtering by a signal from the synthesizer 32c that generates a signal of a predetermined frequency based on the signal of the reference clock 32d in the down converter 32a. Downconverted to frequency. The down-converted intermediate frequency signal is converted into a digital signal by the A / D converter 32 b and output to the baseband digital processing unit 33.

  The baseband digital processing unit 33 performs a process for despreading the spectrum-spread GPS signal. The signal output from the A / D converter 32b to the carrier correlator 33a is multiplied by a signal from a carrier NCO (Number Controlled Oscillator) 33c, which is a numerically controlled oscillator, and the multiplication result is integrated to perform correlation calculation. Is called. The positioning calculation unit 33f controls the carrier NCO 33c through the carrier tracking loop so that a peak value by this correlation calculation is obtained, that is, synchronization with the carrier wave is established.

  The signal from the carrier correlation unit 33a is further output to the PRN code correlation unit 33b. In the PRN code correlation unit 33b, the signal from the carrier correlation unit 33a is multiplied by the signal from the PRN code generation unit 33d that generates the same pseudo-random code as the GPS satellite to be captured based on the signal from the code NCO 33e, Further, the multiplication result is integrated, thereby performing correlation calculation. The positioning calculation unit 33f controls the code NCO 33e through the code tracking loop so that the peak value by this correlation calculation is obtained, that is, synchronization with the PRN code signal included in the GPS signal is established.

  The GPS signal is despread by the above signal processing, and a baseband signal is obtained from the correlation output by the PRN code correlation unit 33b. The positioning calculation unit 33f acquires a GPS message including satellite position information from the obtained baseband signal. In addition, the positioning calculation unit 33f acquires the flight time of the GPS signal based on the generation timing of the PRN code signal generated on the GPS receiver module 3 side, measures the pseudo distance based on the flight time, Based on the phase change amount of the NCO 33c, the speed and direction of the GPS receiver module 3 itself are also calculated.

  In the baseband digital processing unit 33, there are a plurality of reception channels including a carrier correlation unit 33a, a PRN code correlation unit 33b, a carrier NCO 33c, a PRN code generation unit 33d, and a code NCO 33e. For example, it is assumed that there are 8 reception channels in FIG. The positioning calculation unit 33f is a positioning calculation (three-dimensional) that determines the position of the GPS receiver module 3 by geometric calculation based on pseudo distances obtained from four or more of the received signals received by each reception channel. Perform positioning). Data such as positioning results, speed, and direction are passed to the host system via the external interface unit 34.

  The positioning calculation unit 33f detects the reception C / N of the signal received in each reception channel of the baseband digital processing unit 33, selects only the reception C / N exceeding a predetermined threshold and uses it for the positioning calculation. ing. For example, the positioning calculation unit 33f performs two-dimensional positioning when the number of GPS satellites being tracked is three, and performs three-dimensional positioning when the number is four or more.

  The GPS receiver module 3 includes a GPS receiver DC power supply unit 31 and an antenna DC power supply unit 35 that supply an operating voltage to each element based on a power supply voltage supplied from an external power supply (not shown). The GPS receiver DC power supply unit 31 generates a voltage based on a power supply voltage supplied from an external power supply, and operates as an operating voltage on each element of the RF analog processing unit 32, the baseband digital processing unit 33, and the external interface unit 34. Supply. The antenna DC power supply unit 35 generates a voltage based on the power supply voltage supplied from the external power supply, and supplies the voltage to the voltage control circuit 15 of the active antenna 1.

  Here, as described above, the voltage control circuit 15 not only functions as a power supply unit of the active antenna 1 but also has a gain control function of the variable gain LNAs 12 and 14. Gain control of the variable gain LNAs 12 and 14 is performed in cooperation with a part of the circuit of the GPS receiver module 3 and the voltage control circuit 15.

  Specifically, the positioning calculation unit 33f detects the average value (unit: dB) of the upper four received C / N detected in each reception channel of the baseband digital processing unit 33, and the detected result is the antenna. Output to the DC power source 35. In the following, for convenience of explanation, the average value of the detected reception C / N is referred to as “detection C / N”. Since the detected C / N is calculated using an average value of a plurality of good received C / Ns, it accurately represents the current received quality of the GPS signal.

  The antenna DC power supply unit 35 generates an antenna voltage Vd (unit: V) corresponding to the value of the detected C / N from the positioning calculation unit 33f. FIG. 2 is a graph showing the relationship between the antenna voltage Vd and the detection C / N. The vertical axis in FIG. 2 represents the antenna voltage Vd, and the horizontal axis in FIG. 2 represents the detected C / N. As shown in FIG. 2, when the value of the detection C / N is 20 to 40 dB, for example, the antenna DC power supply unit 35 generates an antenna voltage Vd of 4.0 to 5.0 V according to the value. The antenna DC power supply unit 35 supplies the generated antenna voltage Vd to the voltage control circuit 15 as a signal for controlling the gains of the variable gains LNA 12 and 14 as well as the power supply voltage of the active antenna 1. According to another expression, the antenna DC power supply unit 35 superimposes a voltage corresponding to the value of the detected C / N on the power supply voltage to be supplied to the voltage control circuit 15 to be used as the antenna voltage Vd. To supply.

  The voltage control circuit 15 detects the antenna voltage Vd supplied from the antenna DC power supply unit 35 and generates an LNA control voltage Vg (unit: V) corresponding to the detected voltage value. FIG. 3 is a graph showing the relationship between the LNA control voltage Vg and the antenna voltage Vd. The vertical axis in FIG. 3 represents the LNA control voltage Vg, and the horizontal axis in FIG. 3 represents the antenna voltage Vd. As shown in FIG. 3, for example, when the antenna voltage Vd is 4.0 to 5.0 V, the voltage control circuit 15 generates an LNA control voltage Vg of 2.0 to 3.0 V according to the antenna voltage Vd. Generated and output to the variable gain LNAs 12 and 14.

  The gains of the variable gains LNA 12 and 14 are controlled according to the LNA control voltage Vg from the voltage control circuit 15. FIG. 4 is a graph showing the relationship between the gains of the variable gain LNAs 12 and 14 (hereinafter referred to as “LNA gain”) (unit: dB) and the LNA control voltage Vg. The vertical axis in FIG. 4 indicates the LNA gain, and the horizontal axis in FIG. 4 indicates the LNA control voltage Vg. As shown in FIG. 4, when the LNA control voltage Vg is 2.0 to 3.0 V, for example, the gains of the variable gain LNAs 12 and 14 are controlled to 25 to 45 dB according to the LNA control voltage Vg.

  Here, the power supply voltage (antenna voltage Vd in the present embodiment) of a general vehicle-mounted active antenna mounted on a vehicle or the like is, for example, about 5V. Therefore, the LNA control voltage Vg generated using the antenna voltage Vd is an appropriate and reasonable value in order to guarantee the normal operation of the active antenna 1.

  FIG. 5 is a graph showing the relationship between the LNA gain and the detected C / N obtained based on FIGS. The vertical axis in FIG. 5 indicates the LNA gain, and the horizontal axis in FIG. 5 indicates the detected C / N. As shown in FIG. 5, when the detected C / N is in the range of 20 to 40 dB, a part of the GPS receiver module 3 is used to improve the received C / N as the value of the detected C / N is lower. The LNA gain is increased by the cooperation of this circuit and the voltage control circuit 15.

  The RF cable 2 increases the high-frequency signal loss (for example, 0.5 dB / m) in proportion to the gable length. Therefore, the reception C / N (detection C / N) inevitably deteriorates as the cable length of the RF cable 2 increases. For example, when the cable length of the RF cable 2 is 2 m, a high-frequency signal loss of 1 dB occurs, and the detection C / N becomes 35 dB. Even when such a high-frequency signal loss occurs, the LNA gain is set to 31 dB, for example, in order to keep the level of the GPS signal input to the RF analog processing unit 32 above a certain level. Further, for example, when the cable length of the RF cable 2 is 12 m, a high-frequency signal loss of 6 dB occurs and the detection C / N is 30 dB, and when the cable length is 22 m, a high-frequency signal loss of 11 dB occurs. The detection C / N is 25 dB. Even in such a case, the LNA gain is set to 36 dB and 41 dB, respectively, in order to keep the level of the GPS signal input to the RF analog processing unit 32 above a certain level.

  In the GPS unit 100 of the present embodiment, the received C / N (detection C / N) deteriorated according to the cable length is directly detected, and the detection result, that is, the result of taking into account the signal loss in the RF cable 2 is used. By controlling the LNA gain, feedback control is performed so that the level of the GPS signal input to the RF analog processing unit 32 is kept above a certain level. Therefore, it is not necessary to perform individual gain adjustment work and design for the signal amplifier of the active antenna 1 for each gable length of the RF cable 2. Thereby, reduction of development cost, lead time, etc. is achieved, for example.

  In the GPS unit 100 of the present embodiment, the power line of the RF cable 2 is used to control the LNA gain. The power supply line of the RF cable 2 is an existing line for supplying a power supply voltage to the power supply unit of the active antenna 1. That is, according to this embodiment, there is a cost merit that it is not necessary to add a dedicated signal line for controlling the LNA gain to the RF cable 2.

  The above is the description of the embodiment of the present invention. The present invention is not limited to the above-described configuration, and various modifications can be made within the scope of the technical idea of the present invention.

It is a block diagram which shows schematic structure of the GPS unit of embodiment of this invention. It is a graph which shows the relationship between the antenna voltage Vd and detection C / N. It is a graph which shows the relationship between LNA control voltage Vg and antenna voltage Vd. It is a graph which shows the relationship between LNA gain and LNA control voltage Vg. It is a graph which shows the relationship between a LNA gain and detection C / N.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Active antenna 2 RF cable 3 GPS receiver module 11 Antenna element 12, 14 LNA
13 BPF
15 Voltage Control Circuit 31 GPS Receiver DC Power Supply Unit 32 RF Analog Processing Unit 33 Baseband Digital Processing Unit 34 External Interface Unit 35 Antenna DC Power Supply Unit 100 GPS Unit

Claims (5)

In an active antenna having variable gain amplification means for changing the gain of a received signal,
Power supply voltage detection means for detecting a power supply voltage that is supplied from a subsequent device connected to the active antenna and that changes in accordance with the signal quality of the received signal input to the device;
Gain control means for controlling the gain of the variable gain means based on the detected power supply voltage;
An active antenna comprising: An active antenna according to claim 1;
A GPS (Global Positioning System) receiver connected to the active antenna;
A GPS unit having
The GPS receiver is
Reception quality detection means for detecting reception quality of a GPS signal that is the reception signal input from the active antenna;
Power supply voltage generating means for generating a power supply voltage according to the detected reception quality;
Power supply voltage supply means for supplying the generated power supply voltage to the active antenna;
A GPS unit comprising: An active antenna according to claim 1;
A GPS receiver connected to the active antenna;
A GPS unit having
The GPS receiver is
Reception quality detection means for detecting reception quality of a GPS signal that is the reception signal input from the active antenna;
Superimposed voltage generating means for generating a superimposed voltage in which a voltage corresponding to the detected reception quality is superimposed on a power supply voltage to be supplied to the active antenna;
Power supply voltage supply means for supplying the generated superimposed voltage to the active antenna as the power supply voltage;
A GPS unit comprising: The GPS receiver has a plurality of reception channels for receiving GPS signals of the respective GPS satellites,
4. The reception quality detecting means detects an average value of reception qualities of a predetermined number of GPS signals having good reception quality among GPS signals received by each reception channel. A GPS unit according to any one of the above.   The GPS unit according to claim 2, wherein the GPS unit is mounted on a moving body.

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