JP2003229771A - Transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmitter capable of BPSK-modulating reflected waves with a diode being set off. <P>SOLUTION: A transmission circuit 4 is connected to a transmission antenna 3 and a control circuit 5 and is composed of a diode circuit 6 having two series connected varactors 7, and an impedance adjusting circuit 10 composed of a main line 11 and capacitors 12, 13. The control circuit 5 applies reverse-bias voltages of 3 V and 0 V to the diodes 7 to change the impedance of the diode circuit 6. Thus the impedance adjusting circuit 10 changes the impedance of the diode circuit 6, to change the impedance of the transmission circuit 4 with a phase difference of 180°, thereby conducting BPSK-modulation of waves reflected from the antenna 3. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-contact IC, for example.
The present invention relates to a reflection-type transmission device suitable for use as a transponder for identifying a moving object such as a card or an RF tag.

[0002]

2. Description of the Related Art Generally, as a transmitter, a high frequency electromagnetic wave such as a microwave or a millimeter wave transmitted from an interrogator (counterpart) is reflected by an antenna, and the reflected wave is subjected to two-phase phase modulation (hereinafter referred to as BPSK). It is known that data is transmitted to an interrogator by applying (modulation) (for example, Japanese Patent Laid-Open No. 6-104945).

In such a conventional transmitter, a circuit using a diode is connected to the antenna. Then, when transmitting data to the interrogator, the bias voltage applied to the diode is switched between the forward direction and the reverse direction (or zero bias) based on the data, and the ON state and the OFF state of the diode are switched.
As a result, the impedance of the circuit viewed from the antenna changes, so that the reflected wave is modulated according to the change in impedance. As a result, in the related art, the transmitting device itself does not generate a carrier wave and uses a reflected wave as a carrier wave, so that power consumption can be suppressed as much as possible.

[0004]

By the way, in the above-mentioned transmitter according to the prior art, the diode is in the ON state and the O state.
BP for reflected waves by switching between FF state
Since SK modulation is performed, when the diode is turned on, a current of, for example, several μA to several hundreds μA flows through the diode. Therefore, there is a problem that the power consumption of the transmitter increases due to the current flowing through the diode.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a transmitting apparatus capable of performing BPSK modulation on a reflected wave while keeping a diode in an OFF state. .

[0006]

In order to solve the above-mentioned problems, the transmitting device according to the invention of claim 1 is an antenna, a variable capacitance diode connected to the antenna, and a reverse capacitor for applying to the variable capacitance diode. And a control circuit that controls the bias voltage to perform two-phase phase modulation on the reflected wave transmitted from the antenna.

With this configuration, the control circuit can be used to change the reverse bias voltage and adjust the electrostatic capacitance of the variable capacitance diode. As a result, the impedance of the circuit including the variable capacitance diode changes, so that BPSK is applied to the reflected wave reflected from the antenna.
Modulation can be performed. Further, since the reverse bias voltage is always applied to the variable capacitance diode, the variable capacitance diode is held in the OFF state. Therefore, no forward current flows through the variable capacitance diode.

According to a second aspect of the present invention, a plurality of variable capacitance diodes are connected in series between the antenna and the ground.

As a result, in a circuit in which a plurality of variable capacitance diodes are connected in series as compared with a circuit using a single variable capacitance diode, the reactance value of the circuit is the sum of the reactance values of the plurality of variable capacitance diodes. be able to. As a result, when the reverse bias voltage is switched between two values using a control circuit, for example, it is possible to increase the difference between the reactance value when one reverse bias voltage is applied and the reactance value when the other reverse bias voltage is applied. it can.

According to the third aspect of the invention, the plurality of variable capacitance diodes are connected so that the adjacent diodes have opposite polarities.

As a result, the variable capacitance diodes adjacent to each other can have their anode terminals or cathode terminals connected to each other. Therefore, since a common reverse bias voltage can be applied to this connection point, it is not necessary to connect a DC blocking capacitor or an AC blocking choke coil to each variable capacitance diode,
The circuit for driving the variable capacitance diode can be simplified.

According to a fourth aspect of the present invention, there is provided a transmitting device, an antenna, a variable capacitance diode connected to the antenna,
An impedance adjustment circuit provided between the variable capacitance diode and the antenna for adjusting the impedance on the variable capacitance diode side, and a reverse bias voltage applied to the variable capacitance diode are controlled to be switched between two values and transmitted from the antenna. And a control circuit that performs two-phase modulation on the reflected wave.

With this configuration, the control circuit switches the reverse bias voltage between two values and adjusts the capacitance of the variable capacitance diode to change the impedance of the circuit including the variable capacitance diode between two values. . And
The impedance adjustment circuit adjusts the impedance of the circuit including the variable capacitance diode. As a result, the impedance at the frequency of the carrier wave of the transmission signal viewed from the antenna can be changed by two values with a phase difference of 180 ° while setting the absolute value of the reflection coefficient to about 1. Therefore, BPSK modulation can be performed on the reflected wave reflected from the antenna. Further, since the reverse bias voltage is always applied to the variable capacitance diode, the variable capacitance diode is held in the OFF state. For this reason,
A forward current does not flow through the variable capacitance diode.

An impedance adjusting circuit according to a fifth aspect of the present invention includes a main line connecting the antenna and the variable capacitance diode, and a capacitor, a coil or a phase circuit provided on the variable capacitance diode side of the main line. Of the main line, which is located on the antenna side and connected to the main line, is composed of a capacitor having a short-circuited end, a coil or a short-circuit stub, or an open stub having an open end.

Thus, the capacitor, coil or phase circuit provided on the variable capacitance diode side converts the impedance on the variable capacitance diode side, and the transmission on the variable capacitance diode side when the control circuit applies one reverse bias voltage. The impedance at the frequency of the carrier wave of the signal can be arranged near the short circuit point on the Smith chart. In addition, the capacitor, coil, short-circuit stub or open stub provided on the antenna side further converts the converted impedance, and the impedance on the variable capacitance diode side when the control circuit applies one reverse bias voltage is shown on the Smith chart. Of the variable capacitance diode when the other reverse bias voltage is applied can be arranged near the open point on the Smith chart.

Therefore, when the variable capacitance diode side is viewed from the antenna, the phase difference between the two impedances corresponding to the binary reverse bias voltage can be set to about 180 ° and the absolute reflection coefficient by these two impedances can be set. The values can be approximately equal. Thus, by switching the reverse bias voltage between two values based on the data to be transmitted, the reflected wave reflected from the antenna can be BPSK modulated.

According to another aspect of the impedance adjusting circuit of the present invention, a main line connecting the antenna and the variable capacitance diode, and the control circuit provided on the variable capacitance diode side of the main line applies one reverse bias voltage. When the impedance at the carrier frequency of the transmission signal of the variable capacitance diode side is arranged near the short-circuit point on the Smith chart, and the control circuit provided on the antenna side of the main line The impedance at the frequency of the carrier wave of the transmission signal on the variable capacitance diode side when a reverse bias voltage is applied is arranged near the short-circuit point on the Smith chart, and the impedance of the variable capacitance diode side when the other reverse bias voltage is applied. Impedance at the frequency of the carrier wave of the transmission signal is near the open point on the Smith chart It is constituted by the opening point placer to place.

As a result, when the impedance when the variable capacitance diode side is viewed from the antenna is switched between two values in accordance with the binary reverse bias voltage with respect to the frequency of the carrier wave of the transmission signal, these two values are switched. The impedance phase difference can be set to about 180 °, and the absolute values of the two reflection coefficients corresponding to each impedance can be made substantially equal. Therefore, by switching the reverse bias voltage between two values based on the data to be transmitted,
The reflected wave reflected from the antenna can be BPSK modulated.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The following is a detailed description with reference to the accompanying drawings, taking as an example the case where a transmitting device according to an embodiment of the present invention is applied to an on-vehicle device of an automatic toll charging system used in Europe and the like. Explained.

First, FIGS. 1 to 5 show a first embodiment, in which 1 is a receiving antenna, and the receiving antenna 1 is transmitted from a roadside device (not shown) as an interrogator. A receiving circuit 2 for receiving and demodulating electromagnetic waves is connected. On the other hand, 3 is a transmitting antenna, and the transmitting antenna 3
A transmission circuit 4 is connected to the.

A control circuit 5 is connected to the reception circuit 2 and the transmission circuit 4, and the control circuit 5 controls the transmission circuit 4 based on the signal demodulated by the reception circuit 2 to obtain necessary data (information). The signal is transmitted to the roadside device through the transmission circuit 4. Therefore, the receiving antenna 1, the receiving circuit 2 and the control circuit 5 form a receiving device, and the transmitting antenna 3, the transmitting circuit 4 and the control circuit 5 form a transmitting device.

The control circuit 5 applies a voltage of, for example, 0 V to the transmission circuit 4 when the digital data to be transmitted is "0", and a voltage of, for example, 3 V when the data is "1". It is configured to be applied to.

Next, the diode circuit 6 and the impedance adjusting circuit 10 which constitute the transmitting circuit 4 will be described with reference to FIG. It should be noted that all the impedances described below are impedances at the frequency of the carrier wave (reflected wave).

Reference numeral 6 denotes a diode circuit which constitutes the transmission circuit 4, and the diode circuit 6 is constituted by connecting two variable capacitance diodes 7 in series. Also,
Two variable capacitance diodes 7 adjacent to each other are connected so that the directions of the diodes are opposite polarities, for example, cathode terminals are connected to each other. The anode terminal of one variable capacitance diode 7 forming one end of the diode circuit 6 is directly connected to the ground, and the anode terminal of the other variable capacitance diode 7 forming the other end is connected through the impedance adjusting circuit 10. It is connected to the transmitting antenna 3.

The connection point α between the two variable capacitance diodes 7 is connected to the control circuit 5 via a choke coil 8 for AC interruption. On the other hand, the connection point β between the other variable capacitance diode 7 and the impedance adjustment circuit 10 is connected to the ground via the choke coil 9.

Here, the control circuit 5 sets 0 for the connection point α.
When a reverse bias voltage of V or 3 V is applied, a reverse bias voltage is applied between one variable capacitance diode 7 and the ground, and the other variable capacitance diode 7 is also grounded via the choke coil 9. A reverse bias voltage of approximately the same value is applied. Therefore, one connection point α
The reverse bias voltage can be applied to the two variable capacitance diodes 7 together by applying the reverse bias voltage to.

Reference numeral 10 is a transmitting antenna 3 and a diode circuit 6.
An impedance adjustment circuit provided between the main circuit 11 and the main line 11 that connects the diode circuit 6 and the transmission antenna 3 to each other. A capacitor 12 as a short-circuit point locator connected in series in the middle of the line 11,
The main line 11 includes a capacitor 13 which is located on the side of the transmitting antenna 3 and which is connected between the main line 11 and the ground and which serves as an open point arranger.

As will be described later, the capacitor 12 has a point γ between the capacitors 12 and 13 when a reverse bias voltage (for example, 3 V) of either 0 V or 3 V is applied to the variable capacitance diode 7. Impedance A2 when looking at the diode circuit 6 and the capacitor 12
Is arranged near the short-circuit point on the Smith chart (see FIG. 4).

Further, the capacitor 13, when a reverse bias voltage (for example, 3V) of either 0V or 3V is applied to the variable capacitance diode 7 as described later,
The impedance A3 when the diode circuit 6 and the impedance adjusting circuit 10 are viewed from the point δ between the transmitting antenna 3 and the capacitor 13 is arranged near the short-circuit point on the Smith chart. In addition to this, when the other reverse bias voltage (for example, 0 V) is applied, the capacitor 13 starts from the point δ to the diode circuit 6 and the impedance adjusting circuit 10.
The impedance B3 at the time of and is arranged near the open point on the Smith chart (see FIG. 5).

As a result, when the impedance A3, B3 when the transmission circuit 4 including the diode circuit 6 and the impedance adjustment circuit 10 is viewed from the transmission antenna 3 is switched between two values according to the binary reverse bias voltage. The phase difference between the two impedances A3 and B3 can be set to about 180 °, and the absolute values of the two reflection coefficients corresponding to the impedances A3 and B3 can be made substantially equal. Therefore, the reflected wave reflected from the transmitting antenna 3 can be BPSK-modulated by switching between 0 V and 3 V based on the data for transmitting the reverse bias voltage.

The on-vehicle device of the automatic toll charging system according to the present embodiment has the above-mentioned configuration, and its operation will be described below.

First, when the car reaches the charging gate,
A roadside device (interrogator) erected on the side of the road sends a signal to the automobile to urge information on the automobile. At this time, the vehicle-mounted device mounted on the vehicle receives the signal from the roadside device from the receiving antenna 1, demodulates the signal using the receiving circuit 2, and transmits the signal to the control circuit 5. Thereby, the control circuit 5 applies a reverse bias voltage of 0 V or 3 V to the diode circuit 6 based on necessary information (data), and switches the impedance of the transmission circuit 4 with a phase difference of 180 °.

On the other hand, the roadside device transmits a single tone signal having a constant frequency of, for example, 5.8 GHz after transmitting a signal prompting information. As a result, the transmission antenna 3 of the vehicle-mounted device reflects the tone signal from the roadside device, and the transmission circuit 4 uses the reflected wave of this tone signal as a carrier wave and BPSK-modulates this reflected wave by the impedance change of the transmission circuit 4. Call. As a result, the data on the automobile side can be transmitted to the roadside device, and the toll can be automatically charged.

Next, the operation of applying the BPSK modulation to the reflected wave forming the carrier using the transmission circuit 4 will be described with reference to FIGS. 3 to 5.

First, the ideal condition for applying BPSK modulation using the transmission circuit 4 is 3 V by the control circuit 5.
Assuming that the impedance of the transmission circuit 4 when the reverse bias voltage of 1 is applied is ZA and the impedance of the transmission circuit 4 when the reverse bias voltage of 0V is applied is ZB, the results are as follows.

That is, (1) the phase difference between ZA and ZB is 180 °
(2) The absolute value of the reflection coefficient of ZA is equal to the absolute value of the reflection coefficient of ZB (distance from the center point of Smith chart is equal). ), And (3) the absolute values of the reflection coefficients of ZA and ZB are both extremely close to 1 (on the outer peripheral side of the Smith chart).

Therefore, the transmission circuit 4 according to the present embodiment
Is the impedance A of the diode circuit 6 when 3 V is applied.
Impedance B1 of diode circuit 6 when 1 and 0 V are applied
Are impedance-converted using the impedance adjusting circuit 10 to satisfy these three conditions.

Therefore, first, the impedance of the diode circuit 6 will be examined. Here, when the variable capacitance diode 7 is single, the diode circuit 6 when 3V is applied
Diode circuit 6 when impedance of A0 and 0V is applied
The impedance B0 of is arranged at a position shown in FIG. 3 on the Smith chart, for example. At this time, since the variable capacitance diode 7 generally has a relatively small resistance component regardless of the value of the reverse bias voltage, the impedance A0,
B0, which is slightly displaced to the center point O side from the outer circumference circle by the resistance component, is located near the outer circumference side of the Smith chart. Also, these impedances A0,
A phase difference θ0 (∠A0OB0) is formed between B0.

The positions of the impedances A0 and B0 on the Smith chart are determined by the capacitance component of the variable capacitance diode 7, the induction component by the lead terminals (anode terminal, cathode terminal) of the variable capacitance diode 7, the frequency of the carrier wave, and the like. To be done. Then, the variable capacitance diode 7
Form a series resonance circuit composed of the capacitive component and the inductive component. Therefore, when the frequency of the carrier is higher than the resonance frequency of the variable capacitance diode 7 such as 5.8 GHz, the impedances A0 and B0 are located on the inductive side of the short-circuit point on the Smith chart, and the frequency of the carrier is When it is lower than the resonance frequency of the variable capacitance diode 7, the impedances A0 and B0 are located on the capacitive side of the short-circuit point on the Smith chart.

As will be described later, the impedance adjusting circuit 10 adjusts the impedances A0 and B0 when the phase difference θ0 is larger (closer to 180 °) than when the phase difference θ0 is small so that the impedances A0 and B0 meet the BPSK modulation condition. It is relatively easy to perform impedance conversion by using. Therefore, in this embodiment, the two variable capacitance diodes 7 are connected in series to form the diode circuit 6.

As a result, the single variable capacitance diode 7
In the diode circuit 6 in which two variable capacitance diodes 7 are connected in series, the reactance value becomes a value (sum) obtained by adding the reactance values of the two variable capacitance diodes 7 as compared with the case of using. At this time, the difference between the reactance value of the diode circuit 6 when 0V is applied and the reactance value of the diode circuit 6 when 3V is applied is also the difference between the reactance value when 0V is applied and 3V when the single variable capacitance diode 7 is used.
It is a value (sum) obtained by adding two reactance values different from the applied value. As a result, when the control circuit 5 is used to switch the reverse bias voltage between 3V and 0V, the difference between the reactance when 3V is applied and the reactance when 0V is applied is when the single variable capacitance diode 7 is used. It is twice as much.

Therefore, when the diode circuit 6 is viewed from the connection point β, the impedance A1 of the diode circuit 6 when 3V is applied and the impedance B1 of the diode circuit 6 when 0V is applied are as shown in FIG. 3 on the Smith chart, for example. It is placed in a proper position. As a result, the impedance A
1 and B1 move toward the inductive side (clockwise around the center point O) as compared with the impedances A0 and B0, and the phase difference θ1 between the impedances A1 and B1 (∠A1OB
1) becomes larger than the phase difference θ0 between the impedances A0 and B0.

Next, the impedance conversion using the impedance adjusting circuit 10 will be examined.

First, the impedance conversion by the capacitor 12 will be examined. Here, the capacitor 12 is located on the diode circuit 6 side of the main line 11,
Since it is connected in series in the middle of 1, diode circuit 6
The impedance A1 is converted by the capacitor 12 and the circle passing through the impedance A1 and the open point is directed to the capacitive side (counterclockwise about the center point O) as shown in FIG. 4 on the Smith chart. To move. Also, the impedance B of the diode circuit 6
Similarly, 1 also moves on the circle passing through the impedance B1 and the open point toward the capacitive side on the Smith chart.

At this time, since the impedances A1 and B1 are arranged near the outer circumference of the Smith chart, the impedances A1 and B1 move along the vicinity of the outer circumference, and the impedances A2 and B2 after being converted by the capacitor 12 are also the outer circumference. It is placed in the vicinity.

In the present embodiment, the capacitor 1
The capacitance of 2 is set to a value that substantially cancels the inductance component of the impedance A1. As a result, when the diode circuit 6 side is viewed from the point γ between the capacitors 12 and 13 on the main line 11, the impedance A2 when 3V is applied and the impedance B2 when 0V is applied are impedances depending on the capacitance of the capacitor 12. Since they are arranged on the capacitive side of A1 and B1, respectively, the impedance A2 when 3 V is applied is arranged near the short-circuit point. In this embodiment, the capacitance of the capacitor 12 is adjusted so that the impedance A2 is located slightly on the inductive side of the shortest point of the short circuit point.

Next, the impedance conversion by the capacitor 13 will be examined. Here, the capacitor 13 is located on the transmission antenna 3 side of the main line 11,
Since the impedance A2 at the point γ is converted by the capacitor 13 because it is connected between the impedance A2 and the ground, for example, as shown in FIG. 5 on the Smith chart, it is inductive on a circle passing through the impedance A2 and the short-circuit point. Move toward the side (clockwise around the center point O).
Similarly, the impedance B2 at the point γ also moves on the Smith chart on the circle passing through the impedance B2 and the short circuit point toward the inductive side.

At this time, since the impedance A2 is arranged in the vicinity of the short-circuit point, the circle passing through the impedance A2 and the short-circuit point has a very small radius. Therefore, the movement of the impedance A2 on the Smith chart becomes very small. Therefore, when the diode circuit 6 side is viewed from the point δ between the capacitor 13 and the transmitting antenna 3 in the main line 11, the impedance when 3V is applied. A3 is held near the short-circuit point regardless of the capacity of the capacitor 13.

On the other hand, the impedance B2 is arranged at a position distant from the short-circuit point according to the phase difference θ2 (∠A2OB2) with the impedance A2.
The radius of the circle passing through and the short circuit point is close to the radius of the outer circle of the Smith chart, for example. Then, in the present embodiment, the capacitance of the capacitor 13 is set to a value at which the capacitive susceptance of the capacitor 13 substantially cancels the inductive susceptance component of the impedance B2. As a result, when the diode circuit 6 side is viewed from the point δ, 0 V
Since the impedance B3 at the time of application is arranged closer to the inductive side than the impedance B2 according to the capacitive susceptance of the capacitor 13, the converted impedance B3 is arranged near the open point.

Here, the phase difference θ3 with the impedance A2 is the same as the impedance C2 shown as a comparative example in FIG.
When (∠A2OC2) is small, impedance C2
The radius of the circle passing through the short circuit point and the short circuit point becomes smaller according to the phase difference θ3, and may be, for example, half or less of the radius of the outer circle. In this case, even if the impedance C2 is converted by the capacitor 13, the converted impedance C3 is arranged closer to the short-circuit point side than the center point O. As a result,
Phase difference between impedances A3 and C3 becomes 0 ° and BP
Since the condition (1) for SK modulation is not satisfied, BPSK modulation cannot be performed.

When the phase difference θ3 is small, the impedance C3 is located closer to the center point O than the open point, even when the converted impedance C3 is located closer to the open point than the center point O. To be done. As a result, BPSK
Since the modulation condition (3) is not satisfied, the reflection coefficient decreases and the conversion loss in BPSK modulation increases.

On the other hand, since the phase difference θ2 increases / decreases in accordance with the phase difference θ1, the larger the phase difference θ1, the larger the phase difference θ2. Therefore, in this embodiment, the variable capacitance diodes 7 are connected in series over two, and the phase difference θ1 is made larger than in the case where a single variable capacitance diode 7 is used.

Further, the impedance B3 according to the present embodiment is slightly displaced from the open point to the center point O side due to the influence of the resistance component of the variable capacitance diode 7. On the other hand, in the present embodiment, since the impedance A2 is arranged in advance on the inductive side, the converted impedance A3
Is slightly displaced to the center point O side from the short-circuit point. As a result, the distance between the impedance A3 and the center point O can be made substantially equal to the distance between the impedance B3 and the center point O, and the condition (2) for BPSK modulation can be satisfied.

As described above, in the present embodiment, when viewed from the transmitting antenna 3, the impedance A3 of the transmitting circuit 4 when 3V is applied and the impedance B3 of the transmitting circuit 4 when 0V is applied satisfy the three conditions of BPSK modulation. Since it can be satisfied, the reverse bias voltage is set to 0V and 3V by using the control circuit 5.
By switching with, the BPSK modulation can be efficiently performed on the reflected wave reflected from the transmitting antenna 3.

Thus, in this embodiment, since the variable capacitance diode 7 is connected to the transmission antenna 3 and the reverse bias voltage applied to the variable capacitance diode 7 is controlled by using the control circuit 5, the control circuit is controlled. 5, the reverse bias voltage can be changed to adjust the capacitance of the variable capacitance diode 7. As a result, the impedance of the transmission circuit 4 including the variable capacitance diode 7 changes, so that the BPS is applied to the reflected wave reflected from the transmission antenna 3.
K modulation can be performed.

Further, the variable capacitance diode 7 always has 0V.
Alternatively, since the reverse bias voltage of 3V is applied, the variable capacitance diode 7 is held in the OFF state. Therefore, almost no forward current flows through the variable capacitance diode 7, so that the power consumption (current consumption) of the transmission circuit 4 can be reduced.

Since two variable capacitance diodes 7 are connected in series between the transmitting antenna 3 and the ground, the reactance value of the diode circuit 6 at the time of applying 0 V is higher than that when a single variable capacitance diode 7 is used. And the reactance value of the diode circuit 6 when 3 V is applied can be doubled. As a result, the diode circuit 6 when applying 3 V
Diode circuit 6 when impedance of A1 and 0V is applied
Since the phase difference θ1 with the impedance B1 of the BPS can be increased, by using the impedance adjustment circuit 10 including the two capacitors 12 and 13, the BPS
It is possible to easily form the transmission circuit 4 that satisfies the K modulation condition.

Further, since the two variable capacitance diodes 7 are connected so as to have polarities opposite to each other, a common reverse bias voltage can be applied to these connection points α. Therefore, it is not necessary to separately connect a DC blocking capacitor or an AC blocking choke coil to each variable capacitance diode 7 (see FIG. 12), and simplify the circuit for driving the variable capacitance diode 7. You can

An impedance adjusting circuit 10 for adjusting the impedance is provided between the transmitting antenna 3 and the variable capacitance diode 7, and the impedance adjusting circuit 1 is provided.
0 is a main line 11, a capacitor 12 provided on the diode circuit 6 side of the main line 11, and a capacitor connected to the transmitting antenna 3 side of the main line 11 and connected between the main line 11 and ground. It is possible to convert the impedance A1 of the diode circuit 6 when 3 V is applied using the capacitor 12 and arrange the converted impedance A2 seen from the point γ near the short-circuit point on the Smith chart. it can.

Therefore, even if impedance conversion is performed using the capacitor 13, the voltage of 3 V as seen from the transmitting antenna 3 is obtained.
The impedance A3 of the transmission circuit 4 at the time of application can be maintained near the short-circuit point on the Smith chart regardless of the capacity of the capacitor 13. On the other hand, by appropriately setting the capacitance of the capacitor 13, the transmission circuit 4 when 0V is applied
Impedance B3 can be placed near the open point on the Smith chart.

As a result, the phase difference between the impedance A3 when 3 V is applied and the impedance B3 when 0 V is applied can be set to about 180 °, and the absolute values of the reflection coefficients of these impedances A3 and B3 are made substantially equal. be able to. Therefore, by switching the reverse bias voltage between 3V and 0V based on the data to be transmitted, the reflected wave reflected from the transmitting antenna 3 can be efficiently BPSK modulated.

Further, since the impedance adjusting circuit 10 has a simple structure of two capacitors 12 and 13, the frequency of the carrier wave (reflected wave) is high, and the two impedances A1 and A1 due to the capacitance change of the variable capacitance diode 7 are generated.
Even when the phase difference θ1 of B1 is smaller than 180 °, the impedance adjusting circuit 10 can be easily designed and the transmitting circuit 4 for BPSK modulation that satisfies almost ideal conditions can be configured.

Next, FIGS. 6 and 7 show a second embodiment of the present invention. The feature of this embodiment is that an impedance adjusting circuit is replaced by a capacitor connected in series in the middle of the main line. It is configured to connect a phase circuit that shifts the phase (performs a phase shift). In addition, in this embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

Reference numeral 21 is an impedance adjusting circuit according to the present embodiment. The impedance adjusting circuit 21 is provided between the transmitting antenna 3 and the diode circuit 6 like the impedance adjusting circuit 10 according to the first embodiment. There is. Then, the impedance adjusting circuit 21 includes a main line 22 that connects the diode circuit 6 and the transmitting antenna 3.
And a phase circuit 23 as a short-circuit point locator connected to the diode circuit 6 side of the main line 22 and connected between the main line 22 and the ground located on the transmission antenna 3 side of the main line 22. And a capacitor 24 as an open point locator.

The phase circuit 23 is, for example, the main line 22.
It is constituted by a transmission line such as a coaxial line or a strip line having a characteristic impedance equal to, and the impedances A1 and B1 of the diode circuit 6 are rotated clockwise around the center point O on the Smith chart according to the length dimension of the transmission line. Shift in the direction. Therefore, the phase circuit 23
For example, as shown in FIG. 7, the length dimension of the transmission line is set according to the clockwise phase difference φ between the impedance A1 and the short circuit point.

As a result, the phase circuit 23 and the capacitor 2
Among the impedances A2 'and B2' seen from the point γ between the point 4 and 4, the impedance A2 'at the time of applying 3V can be arranged in the vicinity of the short-circuit point, so that the capacitor 24 is provided in the same manner as in the first embodiment. It can be used to move the impedance A2 'to the vicinity of the short-circuit point and the impedance B2' to the vicinity of the open point.

Thus, in this embodiment, it is possible to obtain the same effect as that of the first embodiment.

Next, FIGS. 8 and 9 show a third embodiment of the present invention, which is characterized in that a capacitor connected between the main line and ground in the impedance adjusting circuit. Instead, the configuration is such that a coil (inductor) is connected. In addition, in this embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

Reference numeral 31 denotes an impedance adjusting circuit according to the present embodiment. The impedance adjusting circuit 31 is provided between the transmitting antenna 3 and the diode circuit 6 like the impedance adjusting circuit 10 according to the first embodiment. There is. Then, the impedance adjustment circuit 31 includes a main line 32 that connects the diode circuit 6 and the transmission antenna 3.
A capacitor 33 as a short-circuit point locator connected to the diode circuit 6 side of the main line 32;
Is located on the transmission antenna 3 side and is constituted by a coil 34 as an open point locator connected between the main line 32 and the ground.

The capacitor 33 has a smaller capacity than the capacitor 12 according to the first embodiment. As a result, the capacitor 33 can increase the amount of movement of the impedance of the diode circuit 6 to the capacitive side of the Smith chart. Therefore, as seen from the point γ between the capacitor 33 and the coil 34, as shown in FIG. Of the impedances A2 "and B2", the impedance B2 "when 0 V is applied can be arranged near the short circuit point on the Smith chart. At this time, the impedance B2" when 0 V is applied is slightly more capacitive than the short circuit point. The impedance A2 ″ at the time of applying 3V is also arranged on the capacitive side with respect to the short-circuit point.

On the other hand, since the coil 34 is located on the transmission antenna 3 side of the main line 32 and is connected between the main line 32 and the ground, the impedances A2 "and B2" at the point .gamma.
The impedance is converted by the coil 34, and for example, the impedance A as shown in FIG. 9 on the Smith chart.
On the circle passing through 2 "and B2" and the short-circuit point, the capacitive side (center point O
Counterclockwise around) as a center.

At this time, since the impedance B2 ″ is arranged near the short-circuit point, the impedance B3 ″ when 0 V is applied as viewed from the point δ is maintained near the short-circuit point regardless of the inductance of the coil 34. .

On the other hand, the radius of the circle passing through the impedance A2 ″ and the short-circuit point is close to the radius of the outer circle of the Smith chart, for example. The impedance A3 ″ at the time of applying 3 V can be arranged near the open point.

Thus, in this embodiment, the same operational effect as that of the first embodiment can be obtained.

Next, FIGS. 10 and 11 show the fourth embodiment of the present invention.
The embodiment is characterized in that a coil is connected in series to the diode circuit side on the main line of the impedance adjustment circuit, and a coil is connected between the main line and ground on the transmitting antenna side. It is configured to do. In addition,
In the present embodiment, the same components as those in the first embodiment will be designated by the same reference numerals, and the description thereof will be omitted.

Reference numeral 41 denotes an impedance adjusting circuit according to the present embodiment. The impedance adjusting circuit 41 is provided between the transmitting antenna 3 and the diode circuit 6 as in the impedance adjusting circuit 10 according to the first embodiment. There is. Then, the impedance adjustment circuit 41 includes a main line 42 that connects the diode circuit 6 and the transmission antenna 3.
And a coil 43 as a short-circuit point locator connected to the diode circuit 6 side of the main line 42, and connected between the main line 42 and the ground located on the transmission antenna 3 side of the main line 42. It is constituted by a coil 44 as an open point disposing device.

The transmission circuit 4 according to the present embodiment has the above-mentioned configuration, and next, the impedance adjustment circuit 4
The operation of No. 1 will be described. In the present embodiment, the frequency of the carrier wave is lower than the resonance frequency of the variable capacitance diode 7 when 3V is applied or when 0V is applied.

In this case, when the variable capacitance diode 7 is single, the impedance A0 'of the diode circuit 6 when 3V is applied and the impedance B0' of the diode circuit 6 when 0V is applied are, for example, as shown in FIG. All of them are arranged on the Smith chart at a position on the capacitive side with respect to the short-circuit point, and a phase difference θ0 ′ (∠A0′OB0 ′) is formed between these impedances A0 ′ and B0 ′.

Since the diode circuit 6 has two variable capacitance diodes 7 connected in series, the diode circuit 6 has a reactance value of two variable capacitance diodes 7 as compared with the case where a single variable capacitance diode 7 is used. It becomes a value (sum) obtained by adding the reactance values of 7. As a result, when the diode circuit 6 is viewed from the connection point β, the impedance A1 'of the diode circuit 6 when 3V is applied and the impedance B1' of the diode circuit 6 when 0V is applied are larger than the impedances A0 'and B0'. The phase difference θ between the impedances A1 'and B1'.
1'becomes larger than the phase difference .theta.0 'between the impedances A0' and B0 '.

Next, the coil 43 compares these impedances A1 'and B1' with the impedance A1 on the Smith chart.
A circle passing through 1 ', B1' and the open point is moved toward the inductive side. Then, in the present embodiment, the inductance value of the coil 43 is set to a value that substantially cancels the capacitance component of the impedance B1 ', for example. As a result, when the diode circuit 6 side is viewed from the point γ, the impedance when 0 V is applied is arranged in the vicinity of the short-circuit point, like the impedance B2 ″ in FIG.

The coil 44 further performs impedance conversion on the impedance at the point γ. As a result, when the diode circuit 6 side is viewed from the point δ, the impedance when 0 V is applied can be arranged near the short-circuit point, and the impedance when 3 V is applied can be arranged near the open point.

Thus, this embodiment can also obtain the same operational effect as that of the first embodiment.

In the fourth embodiment, the coil 43
Is set to a value that substantially cancels the capacitance component of the impedance B1 '. However, the present invention is not limited to this. For example, as in the first modification shown in FIG. 12, instead of the coil 43, a coil 45 whose inductance value is set to a value that substantially cancels out the capacitance component of the impedance A1 ′ is provided. Used and coil 4
Instead of 4, the capacitor 46 may be used.

In this case, when the diode circuit 6 side is viewed from the point γ, the impedance when 3 V is applied and the impedance when 0 V is applied are both inductive to the short-circuit point, similar to the impedances A2 and B2 in FIG. Is located in. Therefore, when the diode 46 is viewed from the point δ using the capacitor 46, it is possible to arrange the impedance when 3V is applied near the short-circuit point and the impedance when 0V is applied near the open point. it can.

In the fourth embodiment, the carrier frequency is lower than the resonance frequency of the variable capacitance diode 7 when 3V is applied or when 0V is applied. But,
The present invention is not limited to this, and the carrier frequency may be set to a value between the resonance frequency of the variable capacitance diode 7 when 3V is applied and the resonance frequency of the variable capacitance diode 7 when 0V is applied.

In this case, as in the second modification shown in FIG. 13, the impedance A 0 ″ when 3 V is applied is arranged on the capacitive side of the short-circuit point with respect to the single variable capacitance diode 7, and 0 V is applied. The impedance B0 ″ at that time is arranged on the inductive side of the short-circuit point. On the other hand, the diode circuit 6 in which two variable capacitance diodes 7 are connected in series is
Impedance A1 ″ when V is applied is impedance A0 ″
The impedance B1 ″ when 0V is applied moves to the inductive side of the impedance B0 ″. Therefore, the impedance A of the diode circuit 6
Phase difference θ1 ″ between 1 ″ and B1 ″ is impedance A0 ″, B
The points that are larger than the phase difference θ0 ″ between 0 ″ are the first and fourth points.
This is the same as the embodiment.

Since the impedance A1 ″ is arranged on the capacitive side of the short-circuit point, the point δ can be obtained by using the impedance adjusting circuit 41 similar to that shown in FIG.
When looking at the side of the diode circuit 6 viewed from the above, the impedance when 3 V is applied can be arranged near the short-circuit point, and the impedance when 0 V is applied can be arranged near the open point.

On the other hand, since the impedance B1 ″ is arranged on the inductive side with respect to the short-circuit point, the impedance adjusting circuit 31 similar to that shown in FIG. The impedance when 0 V is applied can be arranged near the short-circuit point, and the impedance when 3 V is applied can be arranged near the open point.

In the fourth embodiment and the first modification, the coils 43 and 45 are connected in series to the main line 42, but instead of the coils 43 and 45, as in the second embodiment. Alternatively, the phase circuits may be connected together.

Further, in the first and second embodiments,
Main lines 11 and 22 of impedance adjustment circuits 10 and 21
It is assumed that the capacitors 13 and 24 are connected between the ground and the ground, but instead of the capacitor connected to the ground as in the third modification shown in FIG. The length of the stub 51 (2
A configuration may be adopted in which a short-circuit stub (where λ: wavelength of carrier wave, n: integer) having a length dimension obtained by adding (n + 1) λ / 4 is connected to the main line 11.

Further, in the third embodiment, the coil 34 is connected between the main line 32 of the impedance adjusting circuit 31 and the ground. However, as in the fourth modification shown in FIG. The short-circuit stub 52 whose end is short-circuited instead of the coil connected to the ground (ground-connected) or the length dimension of the short-circuit stub 52 is (2n + 1) λ
An open stub having a length dimension obtained by adding / 4 may be connected to the main line 11.

Further, in each of the above-described embodiments, the diode circuit 6 has a structure in which two variable capacitance diodes 7 are connected in series so as to be in opposite directions (opposite polarities).
However, the present invention is not limited to this, and for example, as in the fifth modification shown in FIG. 16, the diode circuit 61 includes two variable capacitance diodes 62 and 63 in the same direction (same polarity).
It may be configured to be connected in series so that.

In this case, two variable capacitance diodes 6
A DC blocking capacitor 64 is connected between the two and 63, the cathode terminal of the variable capacitance diode 62 is connected to the impedance adjustment circuit 10, and the anode terminal of the variable capacitance diode 63 is connected to ground. Also,
The control circuit 5 is connected to the cathode terminal of the variable capacitance diode 62 via the choke coil 65, and the choke coil 6 is also connected to the cathode terminal of the variable capacitance diode 63.
The control circuit 5 is connected via 6. Further, the cathode terminal of the variable capacitance diode 62 is connected to the ground via the choke coil 67.

Further, in each of the above embodiments, the two variable capacitance diodes 7 are connected in series to form the diode circuit 6, but a single variable capacitance diode may be used to form the diode circuit. You may comprise a diode circuit by connecting three or more variable capacitance diodes in series.

Further, in each of the above-mentioned embodiments, the case where the invention is applied to the vehicle-mounted device of the automatic toll charging system has been described as an example, but the present invention is not limited to this, and the reflection type BPSK is used.
The present invention can be widely applied to transmitters that perform modulation.

[0096]

As described above in detail, according to the invention of claim 1, the variable capacitance diode is connected to the antenna, and the control circuit controls the reverse bias voltage applied to the variable capacitance diode. Therefore, the capacitance of the variable capacitance diode can be adjusted using the control circuit, and the reflected wave reflected from the antenna can be BPSK modulated. Further, since the variable capacitance diode can be held in the OFF state by the reverse bias voltage, a forward current does not flow through the variable capacitance diode, and the power consumption of the transmission device can be reduced.

According to the invention of claim 2, since a plurality of variable capacitance diodes are connected in series between the antenna and the ground, when the reverse bias voltage is switched between two values by using the control circuit, It is possible to increase the phase difference due to the impedance change on the variable capacitance diode side.
It is possible to easily form a transmitter that satisfies the condition of K modulation.

According to the third aspect of the invention, since the plurality of variable capacitance diodes are connected so as to have polarities opposite to each other, a common reverse bias voltage is applied to the connection point between adjacent variable capacitance diodes. Therefore, the circuit for driving the variable capacitance diode can be simplified.

According to the invention of claim 4, an antenna, a variable capacitance diode connected to the antenna, an impedance adjusting circuit provided between the variable capacitance diode and the antenna, and applied to the variable capacitance diode. And a control circuit for controlling the reverse bias voltage. As a result, the control circuit changes the impedance on the variable capacitance diode side by two values, and the impedance adjustment circuit converts the impedance on the variable capacitance diode side to change the impedance at the carrier frequency of the transmission signal viewed from the antenna, The absolute value of the reflection coefficient can be changed to two values with a phase difference of 180 ° while setting the absolute value to about 1. Therefore, BPSK modulation can be performed on the reflected wave reflected from the antenna. Further, since the variable capacitance diode can be held in the OFF state by the reverse bias voltage, the forward current does not flow through the variable capacitance diode,
The power consumption of the transmitter can be reduced.

According to the fifth aspect of the present invention, the impedance adjusting circuit is provided with a main line connecting the antenna and the variable capacitance diode, and a capacitor, a coil or a capacitor provided on the variable capacitance diode side of the main line. Variable capacitance because it is composed of a phase circuit and a capacitor which is located on the antenna side of the main line and which is connected to the main line and whose end is short-circuited, a coil or a short-circuit stub, or an open stub whose end is open. The impedance on the diode side can be converted. This makes it possible to adapt the impedance when the variable-capacitance diode side is viewed from the antenna including the impedance adjustment circuit to the condition that enables BPSK modulation. Therefore, by switching the reverse bias voltage between two values based on the data to be transmitted, the reflected wave reflected from the antenna is
PSK modulation can be applied.

According to the sixth aspect of the invention, the impedance adjusting circuit is constituted by the main line, the short-circuit point arranging device, and the open point arranging device. As a result, when the impedance when the variable capacitance diode side is viewed from the antenna switches between two values according to the binary reverse bias voltage, these two
The phase difference between two impedances can be set to about 180 °, and the absolute values of the two reflection coefficients corresponding to each impedance can be made substantially equal. Therefore, by switching the reverse bias voltage between two values based on the data to be transmitted, the reflected wave reflected from the antenna can be BPSK modulated.

[Brief description of drawings]

FIG. 1 is a block diagram showing a vehicle-mounted device of an automatic toll charging system according to a first embodiment.

FIG. 2 is a circuit diagram showing a transmission antenna, a transmission circuit, and a control circuit according to the first embodiment.

FIG. 3 is a Smith chart showing the impedance of the diode circuit seen from the connection point β in FIG.

FIG. 4 is a Smith chart showing impedance viewed from a point γ in FIG.

5 is a Smith chart showing the impedance of the transmission circuit viewed from the point δ in FIG. 2. FIG.

FIG. 6 is a circuit diagram showing a transmitting antenna, a transmitting circuit, and a control circuit according to a second embodiment.

FIG. 7 is a Smith chart showing impedance viewed from points β and γ in FIG.

FIG. 8 is a circuit diagram showing a transmitting antenna, a transmitting circuit, and a control circuit according to a third embodiment.

FIG. 9 is a Smith chart showing impedance viewed from points γ and δ in FIG.

FIG. 10 is a circuit diagram showing a transmitting antenna, a transmitting circuit, and a control circuit according to a fourth embodiment.

11 is a Smith chart showing the impedance viewed from the connection point β in FIG.

FIG. 12 is a circuit diagram showing a transmitting antenna, a transmitting circuit, and a control circuit according to a first modification.

FIG. 13 is a Smith chart showing impedance of a diode circuit according to a second modification.

FIG. 14 is a circuit diagram showing a transmitting antenna, a transmitting circuit, and a control circuit according to a third modification.

FIG. 15 is a circuit diagram showing a transmitting antenna, a transmitting circuit, and a control circuit according to a fourth modified example.

FIG. 16 is a circuit diagram showing a transmitting antenna, a transmitting circuit, and a control circuit according to a fifth modification.

[Explanation of symbols]

3 Transmit antenna (antenna) 4 transmitter circuit 5 control circuit 6,61 Diode circuit 7,62,63 Variable capacitance diode 10, 21, 31, 41 Impedance adjustment circuit 11,22,32,42 Main line 12,33 Capacitor (Short Point Arranger) 13,24,46 Capacitor (Open Point Arranger) 23 Phase Circuit (Short Point Arranger) 34 Coil (Open Point Arranger) 43, 45 coil (short-circuit point placement device) 51 Open Stub (Open Point Placer) 52 Short-circuit stub (Open-point placement device)

Claims (6)

[Claims] 1. An antenna, a variable capacitance diode connected to the antenna, and a control circuit for controlling a reverse bias voltage applied to the variable capacitance diode to perform two-phase phase modulation on a reflected wave transmitted from the antenna. A transmitter configured by. 2. The transmitter according to claim 1, wherein a plurality of the variable capacitance diodes are connected in series between the antenna and the ground. 3. The transmitter according to claim 2, wherein the plurality of variable capacitance diodes are connected so that the adjacent diodes have opposite polarities. 4. An antenna, a variable capacitance diode connected to the antenna, an impedance adjustment circuit provided between the variable capacitance diode and the antenna for adjusting impedance on the variable capacitance diode side, and the variable capacitance diode. And a control circuit for performing two-phase phase modulation on a reflected wave transmitted from the antenna by controlling switching of a reverse bias voltage applied to the two values. 5. The impedance adjustment circuit, a main line connecting the antenna and the variable capacitance diode, a capacitor, a coil or a phase circuit provided on the variable capacitance diode side of the main line, The transmitter according to claim 4, wherein the transmitter is formed by a capacitor, a coil, a short-circuit stub or an open stub whose end is opened, which is located on the antenna side of the main line and is connected to the main line. 6. The impedance adjusting circuit is provided with a main line connecting the antenna and the variable capacitance diode, and when the control circuit is provided on the variable capacitance diode side of the main line and one of the reverse bias voltages is applied by the control circuit. A short-circuit point arranging device that arranges the impedance at the frequency of the carrier wave of the transmission signal on the variable capacitance diode side in the vicinity of the short-circuit point on a Smith chart; The impedance at the frequency of the carrier of the transmission signal on the side of the variable capacitance diode when a voltage is applied is arranged near the short-circuit point on the Smith chart, and the transmission signal on the side of the variable capacitance diode when a reverse bias voltage is applied The impedance at the carrier frequency of is placed near the open point on the Smith chart The transmitter according to claim 4, wherein the transmitter comprises an open point locator.