JPH06104944A - Two-phase modulation circuit used as detection circuit - Google Patents

Abstract

PURPOSE:To obtain the two-phase modulation circuit used as a detection circuit with high cost effectiveness in which one diode is used for both the circuits by applying a bias voltage to the detection diode, thereby supplying modulation signals whose phase differs by 180 deg. to the diode. CONSTITUTION:An input wave 12 received by an antenna 11 is detected by a diode 1 and a detection current is given to a modulation signal generator 16 and a switch 8 via the switch 8 of a low frequency circuit 15 and an amplifier 17 or the like. Thus, the generator 16 generates a modulation signal of 1, 0 levels, the switch 8 is opened, a reflected wave 13 of the input wave 12 is modulated based on the modulation signal and the reflected wave 13 is subject two-phase modulation and the result is outputted from an antenna 11. The one diode is used for both the functions to obtain the two-phase modulation circuit used as the detection circuit with high cost effectiveness is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator for a contactor of a contactless ID card system, which comprises an interrogator and a responder that modulates and sends back a modulated wave according to information to be responded to from a microwave emitted from the interrogator. Regarding

[0002]

2. Description of the Related Art "Transistor technology", May, 1992, C, for a transponder requiring modulation circuit of an IC card system.
Q-Publisher, as shown in Appendix p27 of the separate volume, two-phase phase modulation (hereinafter, two-phase PS) with a circuit composed of two microwave switches composed of PIN diodes or EETs.
(Referred to as K). The modulation circuit of the transponder operates only after the detection circuit detects the signal emitted from the interrogator. That is, it is configured to operate in conjunction with the detection circuit which is always in the receivable state.

[0003]

The modulation circuit shown in the above document requires the use of two relatively expensive elements such as a PIN diode or EET. The present invention provides an inexpensive and high-performance two-phase phase modulation circuit that also serves as a detection circuit and that also has a detection circuit function.

[0004]

Means for Solving the Problems 2 Also used as a detection circuit of the present invention
The phase-phase modulation circuit introduces a microwave signal through the main line to the other end of a diode whose one end is electrically grounded, and applies a current having a waveform corresponding to the modulation signal to the diode,
In a circuit that performs two-phase phase modulation on the reflected wave reflected from the diode by utilizing the difference between the impedance when the diode is ON and the impedance when the diode is OFF, the admittance when the diode is viewed from the connection point is ON. Admittance Yoff when Yon and OFF is Yon, Yoff = 1
It is characterized in that a short stub with a grounded tip or an open stub with an open tip satisfying the following relation are connected in parallel to the main line, and a bias voltage is appropriately applied to the diode to serve also as a detection circuit. Normally, the modulation circuit is provided separately, but in the present invention, the diode used in the "two-phase phase modulation circuit" is also used as the detection diode, so that one diode can provide two-phase PSK.
It constitutes a circuit and a detection circuit. Generally, when the diode is used as a switching element in the microwave band, the impedance Zdon observed in the microwave band when a DC current is applied to the diode (when ON) and the impedance Zdoff when no current is applied (when the diode is OFF) are used. To use. In this case, when rational Zdon and Zdoff are displayed on the Smith chart, both Zon and Zoff are on the outermost periphery of the Smith chart, and it is desirable that the phase difference between them is 180 ° (point symmetry with respect to the center of the Smith chart). . If such an ideal diode can be used in a two-phase PSK circuit for a transponder of a contactless ID card system, the reflected wave at the time of ON and the reflected wave at the time of OFF are inverted in phase, and at the same time, there is no reflection loss, so that one An ideal two-phase PSK can be obtained with a diode. However, in a normal diode, Z
The phase difference between don and Zdoff does not become 180 °, and the reflection loss is generally large. For example, typical values of Zdon and Zdoff of the Schottky barrier diode in the 2.5 GHz band are values shown in FIG.
The phase difference between the two is not 180 °, and especially Zdon is inside the Smith chart, indicating that the reflection loss is large. Zdon, Zdo like this
Good characteristics can be obtained with one diode showing the value of ff 2
As a means for obtaining the phase PSK, the inventors of the present application previously add a short stub or an open stub in parallel to the main line in the front stage of the diode, and the phases when the diode is turned on and off are different by 180 ° and the reflection loss is equal. We proposed a method to obtain conditions such as the position of stubs to add, length and characteristic impedance. On the other hand, when such a diode is used as a small-signal detector, almost no current flows, but in order to improve the efficiency, the forward current of 0.2 to
It is well known that a bias voltage Vd of 0.3 V is applied and used. Therefore, one diode has Zo
By providing three states of n, Zof, and Vd application, the two-phase PSK circuit and the detection circuit can be combined.

[0005]

FIG. 1 shows an embodiment of the present invention. The same figure shows board 4.
2 phase PSK circuit constituted by the microstrip line and the low frequency circuit 15. The diode 1 is connected between the main line and one end of the diode 1/4 wavelength open stub 6 for equivalent grounding in the microwave band. Reference numeral 5 is a through hole that penetrates the dielectric of the microstrip line and is electrically connected to the back surface conductor. The short holes 3 are formed by the through holes 5. The modulation voltage of "1" or "0" generated by the modulation signal generator 16 is applied between the terminal 10 and the back conductor (ground) of the substrate 4 to form the resistor 9 and the high impedance line 7 having a length of 1/4 wavelength. A modulated current flows from the main line, the short stub 3, and the through hole 5 to the back conductor through the passing diode 1. The value of the modulation current with respect to the modulation voltage is determined by the resistor 9. It goes without saying that the diode 1 turns on when the modulation voltage is "1" and turns off when the modulation voltage is "0". The open stub 8 and the high impedance line 7 are provided so that the presence of the low frequency circuit 15 including the terminals 10 and 14 does not affect the diode 1 in the microwave band. The distance between the diode 1 and the short stub 3 is L ₁ , the length of the short stub 3 is L ₂ , and the characteristic impedances of the main line 2 and the short stub 3 are Z respectively.
If o and Zstb, turn on when looking at the diode 1 side from point a
Admittance Yon at time and Admittance Yoff at OFF
Can be easily obtained, and the condition of Yon · Yoff = 1 should be satisfied. When the diode having the values of Zdon and Zdoff shown in FIG. 3 is used as the diode _1, good results can be obtained by selecting the value of Zo = Zstb = 47Ω L ₁ = 0.06λg L ₂ = 0.10λg. To be Where λ
g is the line wavelength. Therefore, the incident wave 12 received by the antenna 11 of FIG.
Is radiated to the outside again, but since the phase of the reflected wave 13 differs by 180 ° when the diode 1 is ON and when it is OFF, two-phase PSK is applied. Also, instead of the short stub 3, an open stub with an open tip can obtain similar characteristics by appropriately selecting these values. Based on the above, the operation of FIG. 1 will be described with reference to FIG.
FIG. 2 is an output voltage waveform of the modulation signal generator 16 with the horizontal axis representing time. The transponder of the contactless ID card system must be ready to receive signals from the interrogator at all times. During the waiting time t _d , the modulation signal generator 16 always generates the bias voltage Vb,
The switch 18 is in the ON state. The switch 18 can be easily realized by using, for example, an analog switch. The incident wave 12 received by the antenna 11 which emits a signal from the interrogator at t = t _o is efficiently detected by the diode 1. This is because the bias voltage Vb is always applied by the diode 1. The detection current passes through the switch 18, L,
It is amplified by the amplifier 17 through the smoothing circuit composed of C and R. The output is sent to the modulation signal generator 16 and at the same time transmitted to the switch 18. At this point, the modulation signal generator 16 generates a modulation signal of "1" or "0", and at the same time, the switch 18 is in the OFF state. Becomes Therefore, the two-phase PSK is applied to the reflected wave 13 for the reason described above. Therefore, t _d is the waiting time and t _m is the modulation time. When the modulation ends at t = t ₁ , the waiting time becomes t _d again, the modulation signal generator 16 outputs V _d, and the switch 18 returns to the ON state. Although all of the above-described embodiments have been described with respect to the case where the microstrip line is used, the present invention is not limited to the microstrip line, and it goes without saying that equivalent performance can be obtained even when the triplate line is used. .

[0006]

As described above, according to the present invention, it is possible to provide a two-phase PSK circuit which can also serve as one diode detection circuit.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main part of an embodiment of the present invention.

FIG. 2 is an output voltage waveform diagram of the modulation signal generator 16 according to the embodiment of the present invention.

FIG. 3 is a Smith chart showing the impedance of a diode for explaining the principle of the present invention.

[Explanation of symbols]

 1. Diode 2. Main line 3. Short stub 5. Through hole 6.1 / 4 wavelength open stap 15. Low frequency circuit 16. Modulation signal generator 17. Amplifier 18. switch

Claims (1)

[Claims] 1. A microwave signal is guided to the other end of a diode whose one end is electrically grounded through a main line, a current having a waveform corresponding to a modulation signal is applied to the diode, and when the diode is turned on. In a circuit that performs two-phase phase modulation on the reflected wave reflected from the diode by using the difference between the impedance and the impedance at the time of OFF, the admittance Yon at the time of ON and the admittance at the time of OFF when the diode side is seen from the connection point. A short-circuited stub with a grounded tip or an open stub with an open tip that connects Yoff and Yon · Yoff = 1 is connected in parallel to the main line, and a bias voltage is appropriately applied to the diode to double as a detection circuit. A two-phase phase modulation circuit that also functions as a detection circuit.