JP2001144660A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver that reduces the current consumption, enhances the communication speed with an inexpensive configuration of a reduced circuit scale and prevents malfunction due to a steady-state noise at the same time. SOLUTION: A transistor detection circuit 15 provided with a transistor(TR) 15a receives a reception signal by a reception antenna 13 through a preamplifier circuit 14 employing a TR 14a for its amplifier element. A base band amplifier circuit 16 whose amplifier element is a TR 16a receives a detected output of the transistor (TR) detection circuit 15 through a coupling capacitor 24 and gives its amplified output to a comparator circuit that extracts code information from the received signal. TRs with high transition frequency are adopted for the TRs 14a, 16a, which obtain a gain of about 30 dB or over for a frequency band where the carrier frequency of the received signal is in the order of 100 kHz even when a collector current is set to be several microamperes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus for receiving and demodulating an amplitude-modulated signal including code information, and more particularly to a receiving apparatus suitable for a portable type.

[0002]

2. Description of the Related Art For example, in a smart entry system (passive entry system) for automatically locking / unlocking a vehicle door, a response to an ID request signal transmitted in a coded state from a vehicle is provided. A portable device (so-called smart card) is prepared, and the driver always carries it. Conventionally, such a portable device incorporates a receiving device as shown in FIG. 4 as disclosed in Japanese Patent Application Laid-Open No. 60-159265, for example.

In FIG. 1, a receiving antenna 1 is constituted by a parallel resonance circuit of a coil 1a and a capacitor 1b, and electromagnetically couples an ID request signal transmitted from a vehicle side in a state where code information is amplitude-modulated. To receive. The received signal including such code information is supplied to the diode 2a and the capacitor 2 constituting the detection time constant circuit.
b, after being envelope-detected by a diode detection circuit 2 having a resistor 2c, the signal is amplified by an operational amplifier 3 DC-coupled to the detection circuit 2. The amplified output of the operational amplifier 3 is compared with a predetermined reference voltage in a comparison circuit (not shown), and code information is extracted based on the comparison output. In particular, in the device disclosed in Japanese Patent Application Laid-Open No. 60-159265, when an adverse effect due to an external disturbance wave or external noise (stationary noise, not instantaneous noise) appears, the reference voltage By switching the threshold voltage (reference voltage) of the comparison circuit through the generation circuit, a malfunction due to noise is prevented.

[0004]

In the above-mentioned portable device, it is necessary to keep an ID request signal from the vehicle in a standby state (power-on state) where the ID request signal can always be received. Considering that the battery is a built-in battery, it is necessary to minimize current consumption. In order to increase security, the amount of code information must be increased. However, in such a situation, it is necessary to increase the communication speed with the vehicle in order to ensure a sufficient operating speed of the system. desirable.

However, in the configuration using the operational amplifier 3 to amplify the detection output as in the conventional receiver shown in FIG. 4, when the slew rate is increased and the communication speed is increased. Since there is a situation that current consumption is increased, there is a problem that it is not possible to achieve both low current consumption and high-speed communication. Further, in the conventional configuration, when the voltage level of the received signal is lower than the level corresponding to the forward voltage drop of the detection diode 2a, the detection operation becomes impossible. This will increase the current. Furthermore, in order to prevent malfunction due to noise, as in the device described in Japanese Patent Application Laid-Open No. 60-159265, the reference voltage of the reference generation circuit is switched in accordance with the presence or absence of external interference radio waves and external noise. When the circuit configuration is provided, it is unavoidable that the circuit scale becomes large, resulting in an increase in current consumption and a rise in cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to realize a reduction in current consumption and an improvement in communication speed with a low-cost configuration in which a circuit scale is suppressed, and to reduce stationary noise. It is an object of the present invention to provide a receiving device capable of preventing a malfunction due to the malfunction.

[0007]

To achieve the above object, the means described in claim 1 can be adopted. According to this means, since the transistor amplifier circuit is used to amplify the detection output, the current consumption may increase when the communication speed is increased as in the case where an operational amplifier is used for the amplification. Disappears. That is, the communication speed can be improved while reducing the current consumption. Further, since the transistor detection circuit is used, the level of the reception signal that can perform the detection operation is significantly lower than the case where the diode detection circuit is used. For this reason, it is possible to operate even in a state in which the reception level is minute, and the efficiency can be improved, and also from this aspect, the current consumption can be reduced.
In addition, since the detection circuit and the amplifier circuit are AC-coupled, even when noise is included in the reception signal of the detection circuit, only a change in the signal can be extracted from the detection output. As a result, if the level of the received signal is higher than the noise level, the code information can be extracted. That is, code information can be extracted without switching the reference voltage set in the comparison circuit.
This eliminates the need for providing a circuit configuration for switching the reference voltage as in the related art, and eliminates the possibility of causing a rise in cost due to an increase in circuit scale.

According to the second aspect of the present invention, by using a transistor having a high transition frequency as the amplifying transistor, the carrier of the amplitude modulated signal to be amplified can be amplified even when the current consumption is set to about several μA. Frequency 1
Since the circuit configuration is such that a gain of about 30 dB or more can be obtained in a band on the order of 00 kHz, a significant reduction in current consumption can be realized, which is suitable for, for example, a circuit configuration in which a power source is obtained from a battery. In order to obtain a stable gain of about 30 dB or more in a band with a carrier frequency of about 100 kHz to 200 kHz when the current consumption of the amplifying transistor is reduced to about several μA, a transition frequency (catalog value) is used. Is a number G
A transistor of the order of 10 to several tens of GHz will be used.

According to the third aspect of the present invention, the preamplifier circuit is provided before the detection circuit, so that the sensitivity is improved and the receivable range is widened. Also.
Since the detection operation is performed in the nonlinear region of the detection transistor, the efficiency is greatly improved as compared with the case where a diode detection circuit is used, and the load impedance of the preamplifier circuit is increased. Can also be demonstrated.

According to the fourth aspect of the present invention, by using a transistor having a high transition frequency as an amplifying element of the preamplifier circuit, even if the current consumption is set to about several μA, the amplitude of the amplification target can be improved. Since the circuit configuration is such that a gain of about 30 dB or more can be obtained in a band where the carrier frequency of the modulation signal is on the order of 100 kHz, the current consumption in the preamplifier circuit can be significantly reduced.

[0011] In the case of a portable type using a battery as a power source, the battery life is prolonged due to the reduction in current consumption, and the operation reliability in actual use is improved. Performance is improved.

According to the means described in claim 6, the amplitude modulation signal from the transmitting device on the vehicle side is received by electromagnetic coupling, and the code information extracted from the received signal matches the predetermined code information. Only in the case where the operation command code signal is wirelessly transmitted (answered back) to the vehicle side, the receiving operation of the amplitude modulation signal can be performed only within a limited range centered on the transmitting device, and unnecessary reception is possible. The possibility of performing the operation and the response operation in vain is reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a smart entry system for a vehicle will be described below with reference to FIGS. FIG. 2 schematically shows a configuration of a main part of the smart entry system. In FIG. 2, the smart card 11 carried by the driver
Is configured to be capable of bidirectional communication with a transmission / reception unit 12 (corresponding to a transmission device) provided on the vehicle side. In this case, the transmission / reception unit 12 outputs the ID request signal Sd at a relatively short cycle through the transmission antenna 12a, and outputs the response signal Sd transmitted from the smart card 11 side.
a (corresponding to the operation command code signal) to the receiving antenna 12
b, and is configured to demodulate the received signal and supply it to a vehicle ECU (not shown). The ID request signal Sd is a signal obtained by amplitude-modulating encrypted data including code information composed of serial data, and its carrier frequency is set to, for example, about 134 kHz. The response signal Sa is also a signal obtained by amplitude-modulating encrypted data including code information composed of serial data, and its carrier frequency is set to, for example, about 310 MHz.

The smart card 11 includes a battery (not shown)
, And has the following configuration.
That is, the receiving antenna 13 is constituted by a parallel resonance circuit of a coil 13a and a capacitor 13b.
The D request signal Sd is received by electromagnetic coupling. I received
The D request signal Sd is amplified and amplified through a preamplifier circuit 14, a transistor detector circuit 15, and a baseband amplifier circuit 16.
After the detection, the comparison circuit 17 compares the detected signal with a reference voltage, binarizes the signal, and extracts code information. The receiving device 13, the preamplifier circuit 14, the transistor detection circuit 15, and the baseband amplifier circuit 16 constitute a receiving device 18 according to the present invention.

Transmission / reception control I receiving the output of comparison circuit 17
C19 decodes the code information extracted by the comparison circuit 17 and, when the decoding result matches the predetermined information, through the answerback transmitting device 22 including the RF unit 20 and the transmitting antenna 21. An operation of transmitting the response signal Sa is performed. On the vehicle side receiving the response signal Sa through the transmission / reception unit 12, the vehicle ECU (not shown) decodes the code information extracted from the received response signal Sa, and decodes the decoded result with the preset information. When they coincide with each other, a predetermined load control operation (unlocking and locking operation of the door lock mechanism, operation of permitting engine start, and the like) is performed.

FIG. 1 shows a specific circuit configuration of the receiving device 18. As shown in FIG. In FIG. 1, a preamplifier circuit 14 which receives the output of the receiving antenna 13 via a coupling capacitor 23 amplifies a carrier signal (ID request signal Sd) received through the receiving antenna 13 and has a grounded emitter. It consists of a transistor amplifying circuit of the type. That is, the preamplifier circuit 14
The collector of the npn-type transistor 14a whose emitter is grounded is connected to a power supply terminal + V supplied from a battery (not shown).
And a self-biasing resistor 14c is connected between the collector and base of the transistor 14b.

The transistor detection circuit 15 which receives the amplified output of the preamplifier 14 converts the amplified output (a carrier signal having a frequency of about 134 kHz) to a frequency of 25 kHz.
The emitter of the npn-type transistor 15a, whose collector is connected to the power supply terminal + V, is connected to the ground terminal via a parallel circuit of a capacitor 15b and a resistor 15c as a detection time constant circuit. And the base of the transistor 15a is connected to the collector of the transistor 14a, which is the output point of the preamplifier circuit 14. In this case, a circuit constant is set so that the transistor 15a performs a detection operation in a nonlinear region.

The detection output (baseband signal) of the transistor detection circuit 15 is coupled to a coupling capacitor 24.
The baseband amplifier circuit 16 which receives via the (corresponding to the AC coupling element in the present invention) is also constituted by a transistor emitter circuit of a common emitter type like the preamplifier circuit 14. That is, the baseband amplifier circuit 16 connects the collector of the npn-type transistor 16a whose emitter is grounded to the power supply terminal + V via the load resistor 16b, and connects a self-biasing resistor between the collector and base of the transistor 16b. 16c is connected. Then, the amplified output of the baseband amplifier circuit 16 is provided to the comparison circuit 17 (see FIG. 2) via the coupling capacitor 25.

In this case, the transistors 14a and 16a in the preamplifier 14 and the baseband amplifier 16 are used.
As a, a transition frequency fT of several GHz or more is used. Accordingly, even when the circuit constant of the receiving device 18 is set to a state where the collector current (consumption current) of each of the transistors 14a and 16a is about several μA, the received ID request signal Sd (amplitude modulation signal) The configuration is such that a gain (small signal current amplification factor) of about 30 dB or more can be obtained in a band with a carrier frequency on the order of 100 kHz (and a band on the order of 25 kHz corresponding to the frequency of the baseband signal).

That is, for example, as transistors 14a and 16a, fT = 10 GHz (collector current is 7 mA).
Transistor (for example, 2SC)
5095), the collector current is 2 μA
In this case, the gain (small signal current amplification factor) shows a frequency characteristic as shown in FIG. In the case of this embodiment, the carrier frequency of the ID request signal Sd to be amplified is 134 kHz.
Since the frequency is set to about z and the baseband frequency is set to about 25 kHz, a gain of about 32.5 dB or about 32.5 dB can be obtained by applying the frequency characteristics of FIG.

According to the above-described embodiment, the baseband amplifying circuit 16 composed of a transistor amplifying circuit is used for amplifying the detection output by the transistor detecting circuit 15; As in the configuration, when the communication speed is increased, there is no possibility that current consumption increases. That is, since the communication speed can be improved while reducing the current consumption, it is useful when an ID request signal Sd including code information composed of serial data is received. In addition, since the transistor detection circuit 15 is used, the level of a reception signal that can be detected is significantly lower than that in the case where a diode detection circuit is used. For this reason, it is possible to operate even in a state where the reception level is minute, and the efficiency can be improved,
From this aspect as well, low current consumption can be realized.

Moreover, since the transistor detection circuit 15 and the baseband amplification circuit 16 are AC-coupled by the coupling capacitor 24, even if the reception signal of the transistor detection circuit 15 includes noise, Only the change in the signal can be extracted from the detection output. As a result, if the level of the received signal is equal to or higher than the noise level, the comparison circuit 17 can extract the code information. That is, it is possible to extract the code information without switching the reference voltage set in the comparison circuit 17, so that there is no need to provide a circuit configuration for switching the reference voltage as in the related art. This eliminates the risk of a rise in cost due to an increase in circuit scale.

Further, by using transistors 14a and 16a having a transition frequency fT of about several GHz or more as amplification elements for the preamplifier circuit 14 and the baseband amplifier circuit 16, their collector currents become about several μA. And a circuit configuration such that a gain of about 30 dB or more can be obtained in a band where the carrier frequency of the received ID request signal Sd is about 134 kHz (and a band on the order of 25 kHz corresponding to the frequency of the baseband signal) even when set to Therefore, the current consumption can be significantly reduced, which is suitable for a circuit configuration in which the power supply of the receiving device 18 is obtained from a battery as in the present embodiment. More specifically, when the smart card 11 is built in a portable smart card 11 that uses a battery as a power source as in the present embodiment, the battery life is extended as the current consumption is reduced. The operational reliability in actual use is improved.

Moreover, as a result of the preamplifier circuit 14 being provided before the transistor detection circuit 15, the sensitivity is improved and the receivable range is widened. Further, since the detection transistor 15a is configured to perform the detection operation in the non-linear region, the efficiency is greatly improved as compared with the case where the diode detection circuit is used.
Since the load impedance of the preamplifier circuit 14 increases, the impedance conversion function can also be exhibited.

Further, the receiving device 18 in the smart card 11 receives the ID request signal Sd from the transmitting / receiving unit 12 on the vehicle side by electromagnetic coupling, and the code information extracted from the received signal is set to the predetermined code information. The response signal Sa is transmitted wirelessly (answer back) to the vehicle side only when the
On the other hand, the reception operation of the ID request signal Sd can be performed only within a limited range centered on the transmission / reception unit 12, and the possibility of performing unnecessary reception operations and response operations to them is reduced. This is advantageous in achieving the realization.

It should be noted that the present invention is not limited to the above-described embodiment, but can be modified or expanded as follows. The preamplifier circuit 14 may be provided as needed. Further, an FET may be used as a detection element of the detection circuit or an amplification element of the preamplifier circuit and the amplification circuit. The present invention is not limited to the smart entry system, and can be applied to a receiving device for another system or device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a smart entry system.

FIG. 3 is a diagram showing a frequency characteristic of a transistor gain.

FIG. 4 is a diagram corresponding to FIG. 1 showing a conventional configuration.

[Explanation of symbols]

11 is a smart card, 12 is a transmitting / receiving unit (transmitting device), 13 is a receiving antenna, 14 is a preamplifier circuit, 14
a is a transistor, 15 is a detection circuit, 15a is a transistor, 16 is a baseband amplifier circuit, 16a is a transistor, 17 is a comparison circuit, 18 is a receiving device, 22 is a transmitting device for answer back, and 24 is a coupling capacitor (AC coupling). Element).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 1/16 H04B 1/16 Z 5/02 5/02 H04Q 9/00 301 H04Q 9/00 301B 301A 9 / 14 9/14 J (72) Inventor Takahide Kitahara 1-1-1 Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Hiroki Okada 1-Toyota-cho, Toyota-shi, Aichi Prefecture Inside Toyota Motor Corporation F-term (reference) 2E250 AA21 BB36 BB65 FF23 FF36 JJ44 LL01 3D020 BA13 BB01 BE03 5K012 AB03 AC06 AC08 AC11 BA02 5K048 AA08 AA16 BA42 BA53 DB01 DC01 EA16 EB02 HA04 HA06 HA11 HA37 5K061 AA02 EB01 JJ01 CB02

Claims (6)

[Claims] 1. A detection circuit for detecting an amplitude-modulated signal containing code information, an amplification circuit for amplifying a detection output of the detection circuit, and comparing the amplification output of the amplification circuit with a preset reference voltage. A receiving circuit comprising a comparing circuit for extracting the code information, wherein the detecting circuit is configured as a transistor detecting circuit, and the amplifying circuit is configured as a transistor amplifying circuit, and an alternating current is supplied between the detecting circuit and the amplifying circuit. A receiving device comprising a coupling element. 2. The use of a transistor having a high transition frequency as an amplifying transistor included in the amplifying circuit, so that the carrier frequency of the amplitude-modulated signal is in the order of 100 kHz even when the current consumption is set to about several μA. 2. The receiving apparatus according to claim 1, wherein the circuit is configured to obtain a gain of about 30 dB or more in a band. 3. A preamplifier circuit for amplifying a received signal at a stage preceding the detection circuit, wherein the detection circuit is configured to perform a detection operation in a non-linear region of a detection transistor. 3. The receiving device according to 1 or 2. 4. The receiving apparatus according to claim 3, wherein a transistor having a high transition frequency is used as an amplifying element of the preamplifier circuit, so that even when the current consumption is set to about several μA, the amplitude is reduced. The carrier frequency of the modulated signal is 30 in the band of 100 kHz order.
A receiving device having a circuit configuration capable of obtaining a gain of about dB or more. 5. The receiving device according to claim 1, wherein the receiving device is configured as a portable type using a battery as a power source. 6. The receiving device according to claim 5, wherein: a receiving antenna which receives an amplitude modulation signal including code information from a transmitting device mounted on a vehicle by electromagnetic coupling and supplies the amplitude modulated signal to the detection circuit; Answerback transmission for wirelessly transmitting an operation command code signal to the vehicle only when code information extracted from the received signal through the detection circuit, amplification circuit, and comparison circuit matches predetermined code information. A receiving device comprising: a receiving device;