JP2011101086A - Portable terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a portable terminal, wherein when transmission power efficiency is set not to readily lower, when executing a control so that there is no change in information-readable distance due to self heat generation of an amplifier circuit. <P>SOLUTION: The output of a thermistor 9, arranged near a power amplifier 6 is binarized by a second A/D conversion circuit 13 via a switching circuit 17; when the binary voltage becomes a threshold voltage or higher, that is, when the temperature T of the thermistor 9 becomes a threshold temperature Tth or higher, the output to an operation point adjustment circuit 21 of a logic processing circuit 10 is changed; and the operation point of the power amplifier 6 becomes high, and the output of the power amplifier 6 rises. Thus, since the output power decline due to the steep temperature rise of the power amplifier 6 is corrected, the transmission power efficiency becomes less apt to be lowered. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a portable terminal having a function of reading information recorded on an RFID tag by communicating with the RFID tag by radio waves.

  FIG. 9 is an explanatory diagram showing a part of the internal structure of a portable terminal that communicates with a conventional RFID tag. A conventional portable terminal 50 includes an RF module 56 on which a modulation circuit, a demodulation circuit, and the like are mounted, and a microstrip antenna 55 electrically connected to the RF module 56. The RF module 56 includes an amplifier circuit 52 that amplifies the RF signal output from the modulation circuit.

In the portable terminal 50 having such a structure, when the continuous use time becomes long, the amplification circuit 52 self-heats, the output power decreases, and the distance at which information of the RFID tag can be read (hereinafter referred to as information readable distance). ) Becomes shorter, and there is a problem that the feeling of the reading operation is changed.
Therefore, a portable terminal that monitors the output of the amplifier circuit and controls the output power to be constant so that the information readable distance does not change to prevent the reading operation feeling from changing is proposed. Has been.

  FIG. 10 is an explanatory diagram showing a part of the electrical configuration of the mobile terminal omitted. The portable terminal 60 includes an RF control circuit 61 that controls transmission output, an amplifier circuit 52, a distributor 62 that distributes the output of the amplifier circuit 52, and an RF signal output from the amplifier circuit 52 through the distributor 62. As an antenna circuit 63 that outputs as follows.

  The output of the amplifier circuit 52 is distributed by the distributor 62 and fed back to the RF control circuit 61. Then, the RF control circuit 61 detects the amplitude or power of the feedback output, and controls the output of the amplifier circuit 52 to be constant based on the detection result.

JP 2006-279201 A (14th paragraph, FIG. 1)

  However, since the conventional portable terminal 60 shown in FIG. 10 distributes the output of the amplifier circuit 52 by the distributor 62, the output from the amplifier circuit 52 to the antenna circuit 63 decreases by the amount of the distribution. There is a problem that efficiency decreases.

  Accordingly, the present invention has been made to solve the above-described problem, and realizes a portable terminal in which transmission power efficiency is unlikely to decrease when control is performed so that the information readable distance does not change due to self-heating of the amplifier circuit. For the purpose.

  In order to achieve the above object, the first feature of the present invention is that an amplifier circuit (6) for amplifying the output of the modulation circuit (15) and an antenna (4) for transmitting the output of the amplifier circuit as a radio wave. A temperature detecting element (9) for outputting a signal corresponding to the temperature of the amplifier circuit in a portable terminal having a function of reading information recorded on the RFID tag by communicating with the RFID tag by the radio wave; A temperature measurement unit (10a) for measuring the temperature of the amplification circuit based on a signal output from the temperature detection element, and a temperature (T) measured by the temperature measurement unit is equal to or greater than a threshold value (Tth) And a control circuit (21) for increasing the output of the amplifier circuit.

  According to a second feature of the present invention, in the first feature described above, the control circuit (21) has at least a function of increasing the output of the amplifier circuit by changing the operating point of the amplifier circuit (6). Is to have.

  According to a third feature of the present invention, in the first or second feature described above, the modulation circuit (15) is an amplitude modulation circuit, and the control circuit controls a modulation signal input to the modulation circuit. Thus, at least the function of increasing the output level of the modulation circuit is provided.

  According to a fourth feature of the present invention, in any one of the first to third features described above, the control circuit increases the input level of the amplifier circuit (6), thereby increasing the output of the amplifier circuit. It is to have at least a function of raising the level.

  According to a fifth feature of the present invention, in any one of the first to fourth features described above, the temperature measurement unit (10a) is configured so that the amplification circuit ( 6) To measure the temperature.

  A sixth feature of the present invention is that, in the fifth feature described above, the temperature measuring section (10a) measures the temperature of the amplifier circuit (6) in a processing routine for performing carrier sense. Here, the carrier sense is a process for confirming whether or not a frequency channel to be used in the mobile terminal is unused.

  According to a seventh feature of the present invention, in any one of the first to sixth features described above, a demodulation circuit (19, 20) for demodulating a radio wave received from the RFID tag, and an output of the demodulation circuit A / D conversion circuits (12, 13) for A / D conversion, and the temperature measurement unit (10a) converts the signal output from the temperature detection element (9) into the A / D conversion circuit. A / D conversion is performed, and the temperature of the amplifier circuit (6) is measured based on the converted digital value.

  According to an eighth aspect of the present invention, in the seventh aspect described above, the demodulation circuit (19, 20) includes an I demodulation circuit (19) for I-demodulating a radio wave received from the RFID tag, and the RFID A Q demodulation circuit (20) for Q-demodulating the radio wave received from the tag, and the A / D conversion circuit (12, 13) performs a first A / D conversion on the output of the I demodulation circuit. A / D conversion circuit (12) and a second A / D conversion circuit (13) for A / D converting the output of the Q demodulation circuit, and the temperature measurement unit (10a) The signal output from the temperature detection element (9) is A / D converted using one of the first and second A / D conversion circuits, and the amplifier circuit (6) is based on the converted digital value. ) To measure the temperature.

  According to a ninth feature of the present invention, in any one of the first to eighth features described above, the antenna (4) is a microstrip antenna, and heat generated from the amplifier circuit (6) is transferred to the microstrip. The structure is to transmit to the strip antenna.

  According to a tenth feature of the present invention, in the ninth feature described above, the microstrip antenna (4) includes a dielectric (4a) made of ceramics, and a conductive pattern ( 4b) and a circuit board (5) integrally disposed on the back surface of the dielectric, and the amplifier circuit (6) is disposed on the circuit board.

  In addition, the code | symbol in each said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

According to the first feature of the present invention, when the temperature detecting element outputs a signal corresponding to the temperature of the amplifier circuit, the temperature measuring circuit measures the temperature of the amplifier circuit based on the signal, and the measured temperature is If it is equal to or greater than the threshold value, the control circuit can increase the output of the amplifier circuit and correct the output decrease due to the temperature increase.
Therefore, since the output of the amplifier circuit is not distributed, the transmission power efficiency is unlikely to decrease.

According to the second feature of the present invention, by changing the operating point of the amplifier circuit, it is possible to increase the output of the amplifier circuit and correct the output decrease due to the temperature increase.
Therefore, since the output of the amplifier circuit is not distributed, the transmission power efficiency is unlikely to decrease.

According to the third aspect of the present invention, by controlling the modulation signal input to the modulation circuit, the output level of the modulation circuit is increased, thereby increasing the output of the amplifier circuit and reducing the output due to temperature rise. It can be corrected.
Therefore, since the output of the amplifier circuit is not distributed, the transmission power efficiency is unlikely to decrease.

According to the fourth feature of the present invention, by increasing the input level of the amplifier circuit, it is possible to increase the output of the amplifier circuit and correct the output decrease due to the temperature increase.
Therefore, since the output of the amplifier circuit is not distributed, the transmission power efficiency is unlikely to decrease.

  According to the fifth aspect of the present invention, the temperature measurement circuit measures the temperature of the amplifier circuit before starting communication with the RFID tag by radio waves, and therefore starts communication with the RFID tag with the transmission power corrected. can do.

For example, as in the sixth aspect of the present invention, if the temperature of the amplifier circuit is measured in the processing routine for performing carrier sense, communication with the RFID tag can be started with the transmission power corrected. .
Therefore, since the change in the information readable distance can be reduced, the reading operation feeling is hardly changed.

In particular, even when the mobile terminal is continuously used, carrier sensing is performed at regular intervals, so that the temperature of the amplifier circuit can be measured each time carrier sensing is performed.
Therefore, even when the portable terminal is continuously used, the rapid temperature rise of the amplifier circuit can be mitigated, so that the transmission power efficiency is hardly lowered and the information readable distance is hardly shortened.

  According to the seventh aspect of the present invention, the signal output from the temperature detection element is A / D converted by using an A / D conversion circuit for A / D converting the output of the demodulation circuit, and the converted digital Since the temperature of the amplifier circuit can be measured based on the value, it is not necessary to provide a dedicated A / D conversion circuit for temperature measurement, so that the manufacturing cost required for temperature measurement can be suppressed.

For example, as in the eighth feature of the present invention, a first A / D conversion circuit for A / D converting the output of the I demodulation circuit, and a second A / D conversion for A / D conversion of the output of the Q demodulation circuit. In the case of a configuration including a D conversion circuit, one of the first and second A / D conversion circuits can be used.
In particular, when carrier sensing is performed based on the amplitude of a carrier (carrier wave) transmitted from another mobile terminal, the amplitude of the signal demodulated by one of the I demodulation circuit and the Q demodulation circuit Therefore, the temperature of the amplifier circuit can be measured using the A / D conversion circuit that is not used in carrier sense.

According to the ninth aspect of the present invention, since heat generated from the amplifier circuit can be transmitted to the microstrip antenna, a sudden temperature rise of the amplifier circuit can be mitigated.
Therefore, since the transmission power efficiency is difficult to decrease and the information readable distance is difficult to be shortened, the reading operation feeling is difficult to change.

In particular, according to the tenth feature of the present invention, the heat generated from the amplifier circuit can be transferred to the dielectric formed of ceramics, so the heat generated from the amplifier circuit can be efficiently dissipated, A sudden temperature rise in the amplifier circuit can be effectively mitigated.
Therefore, the transmission power efficiency is less likely to be further reduced, and the information readable distance is further unlikely to be changed, so that the reading operation feeling is further unlikely to change.

It is explanatory drawing which abbreviate | omits and shows a part of internal structure of the portable terminal which concerns on 1st Embodiment. It is the expansion perspective view which looked at the surface of the microstrip antenna 4 from diagonally upward. FIG. 3 is a rear view of FIG. 2. It is explanatory drawing which abbreviate | omits and shows the part relevant to reading of optical information among the main electrical structures of the portable terminal. 3 is a circuit diagram of an operating point adjustment circuit 21 and a power amplifier 6. FIG. 4 is a flowchart showing a flow of carrier control processing executed by a CPU of the logic processing circuit 10. It is explanatory drawing which shows the main electrical structures of the portable terminal which concerns on other embodiment. It is explanatory drawing of the microstrip antenna with which the portable terminal which concerns on other embodiment was equipped. It is explanatory drawing which abbreviate | omits and shows the internal structure of the conventional portable terminal. It is explanatory drawing which abbreviate | omits and shows a part of electrical structure of the conventional portable terminal.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a part of the internal structure of the mobile terminal according to this embodiment.

[Main components of mobile terminals]
As shown in FIG. 1, the mobile terminal 1 includes a case 2. The front surface 2a of the case 2 is provided with a key operation unit, a display unit for displaying a reading result, and the like (not shown), and the back surface 2b of the case 2 is provided with a trigger switch (not shown). ing. Inside the case 2, a microstrip antenna 4 for communicating with the RFID tag is incorporated. A power supply circuit board 5 is integrally provided on the back surface of the microstrip antenna 4. A power amplifier 6 for amplifying an RF signal and a temperature of the power amplifier 6 are detected on the back surface of the power supply circuit board 5. For this purpose, a thermistor 9 and a circulator 8 are provided.

In this way, by providing the power amplifier 6 that generates heat by circuit operation on the back surface of the power supply circuit board 5, the heat generated from the power amplifier 6 is transmitted from the power supply circuit board 5 to the microstrip antenna 4, and the microstrip antenna 4. Can dissipate heat. Thereby, since the rapid temperature rise of the power amplifier 6 can be relieved, the output power efficiency of the power amplifier 6 due to the sudden temperature rise can be hardly lowered.
Below the feeder circuit board 5, an RF module 22 on which a modulation circuit, a demodulation circuit, and the like are mounted is disposed with a space therebetween. In addition, an optical information reading module 30 for reading optical information such as a barcode and a two-dimensional code is built in the case 2.

[Main configuration of microstrip antenna]
FIG. 2 is an enlarged perspective view of the surface of the microstrip antenna 4 as viewed obliquely from above, and FIG. 3 is a back view of FIG.

  As shown in FIG. 2, the microstrip antenna 4 includes a dielectric 4a, an antenna element 4b formed on the surface of the dielectric 4a, and an antenna ground portion 4c formed on the surface of the feeder circuit board 5. Prepare. A feeding point 7 is formed on the antenna element 4b.

  As shown in FIG. 3, a power amplifier 6 and a circulator 8 that controls the RF signal output from the power amplifier 6 so as not to flow backward to the receiving circuit side are provided on the back surface of the power supply circuit board 5. . A thermistor 9 is provided in the vicinity of the power amplifier 6 and in a region where heat generated from the power amplifier 6 is easy to transfer (for example, within 10 mm from the end of the power amplifier 6).

  With this configuration, the heat generated from the power amplifier 6 is dissipated to the surroundings through the dielectric 4a, so that the rapid temperature rise of the power amplifier 6 is alleviated. Further, since the temperature rise of the power amplifier 6 is moderate, the heat generated from the power amplifier 6 is transferred to the thermistor 9 and the resistance value of the thermistor 9 also changes gently. For this reason, since the thermistor 9 outputs a signal corresponding to the temperature rise of the power amplifier 6, the temperature of the thermistor 9, that is, the temperature of the power amplifier 6 can be measured substantially accurately. Furthermore, since the line length from the power amplifier 6 to the feeding point 7 via the circulator 8 can be minimized, the output power of the power amplifier 6 can be supplied to the antenna element 4b with minimum loss.

  In this embodiment, the microstrip antenna 4 is formed in a square and transmits linearly polarized waves. The dielectric 4a is made of a dielectric material such as ceramics or synthetic resin (for example, elastomer). The antenna element 4b and the antenna ground portion 4c are each formed of a conductive material whose main component is silver, aluminum, copper, or the like.

[Electric configuration of mobile terminal]
FIG. 4 is an explanatory diagram illustrating a main electrical configuration of the mobile terminal 1 with a portion related to reading of optical information omitted. As shown in the figure, the mobile terminal 1 includes a logic processing circuit 10, a D / A conversion circuit 23, a bandpass filter circuit (BPF) 11, an oscillation circuit 14, a modulation circuit 15, a power amplifier 6, The operating point adjusting circuit 21, the circulator 8, the thermistor 9, the I demodulating circuit 19, the Q demodulating circuit 20, the variable band pass filter circuit 16, the band pass filter circuit 18, and the first A / D conversion circuit 12. A second A / D conversion circuit 13 and a switching circuit 17.

  The logic processing circuit 10 includes a CPU, a ROM, a RAM, and the like (not shown), and controls the operation of the mobile terminal 1 according to an operation signal given from the operation unit. In addition, the logic processing circuit 10 generates transmission data and outputs it to the D / A conversion circuit 23, decoding the data input from the first and second A / D conversion circuits 12 and 13, A process for measuring the temperature of the thermistor 9 based on the data input from the D conversion circuit 13 and a process for adjusting the output power of the power amplifier 6 based on the temperature measurement result are executed.

  The D / A conversion circuit 23 converts the transmission data output from the logic processing circuit 10 into an analog modulation signal, and outputs the modulation signal to the bandpass filter circuit 11. The oscillation circuit 14 supplies the oscillation signal to the modulation circuit 15 as a carrier wave signal. The modulation circuit 15 performs ASK (Amplitude Shift Keying) modulation on the carrier wave signal supplied from the oscillation circuit 14 with the modulation signal output from the bandpass filter circuit 11. The RF signal output from the modulation circuit 15 is amplified with a predetermined amplification factor by the power amplifier 6, passes through the circulator 8, and is transmitted from the microstrip antenna 4 as a radio signal. The circulator 8 prevents the RF signal output from the power amplifier 6 from flowing backward to the receiving side.

  The received signal received by the microstrip antenna 4 is demodulated in the I demodulating circuit 19 and the Q demodulating circuit 20 using carrier signals whose phases are different from each other by 90 degrees. In other words, in order to avoid that the signal received from the RFID tag cannot be detected due to the phase difference between the carrier signal of the signal transmitted to the RFID tag and the carrier signal of the signal received from the RFID tag, the carrier signal and its phase are The received signal is IQ detected using the signal shifted by 90 °.

  The I signal output from the I demodulation circuit 19 is binarized by the first A / D conversion circuit 12 through the variable band pass filter circuit 16. The Q signal output from the Q demodulation circuit 20 is binarized by the second A / D conversion circuit 13 through the band-pass filter circuit 18. The reception data I binarized by the first A / D conversion circuit 12 and the reception data Q binarized by the second A / D conversion circuit 13 are input to the logic processing circuit 10. Of the data I and Q, the data that has been correctly restored is adopted.

  The thermistor 9 changes its resistance value corresponding to the temperature of the power amplifier 6. That is, the thermistor 9 outputs a signal corresponding to the temperature of the power amplifier 6. In this embodiment, the thermistor 9 is an NTC (negative temperature coefficient) thermistor whose resistance value decreases as the temperature rises.

  The switching circuit 17 electrically connected to the thermistor 9 switches the input from the bandpass filter circuit 18 to the thermistor 9 in response to a command from the logic processing circuit 10. That is, the switching circuit 17 controls so that the output of the thermistor 9 is input to the second A / D conversion circuit 13. Then, the second A / D conversion circuit 13 binarizes the output voltage of the thermistor 9 and outputs it to the logic processing circuit 10. The temperature measurement unit 10a mounted on the logic processing circuit 10 compares the input binarized voltage with a threshold voltage stored in advance in a ROM or the like, and based on the comparison result, the temperature of the thermistor 9 is equal to or higher than the threshold temperature. It is determined whether or not.

When performing carrier sense, the presence / absence of a carrier is determined based on the amplitude of the I-demodulated received signal, that is, the size of the received data I output from the first A / D conversion circuit 12. As will be described in detail later, when this carrier sense is performed, the output of the thermistor 9 is binarized using the second A / D conversion circuit 13, and the temperature of the thermistor 9 is measured based on the binarized data. Warm up.
In this way, since the A / D conversion circuit used for demodulating the received signal is also used, a dedicated A / D conversion circuit for A / D converting the output voltage of the thermistor 9 becomes unnecessary. The manufacturing cost required to measure the temperature can be suppressed.

  When the logic processing circuit 10 determines that the binarized voltage is equal to or higher than the threshold voltage, that is, the temperature of the thermistor 9 is equal to or higher than the threshold temperature, the operating point adjustment circuit 21 is operated. The operating point adjustment circuit 21 adjusts the operating point of the power amplifier 6 so that the output power of the power amplifier 6 increases. That is, when the temperature of the power amplifier 6 becomes equal to or higher than the threshold temperature, the output voltage of the thermistor 9 reaches the threshold voltage, the operating point adjustment circuit 21 adjusts the operating point of the power amplifier 6, and the output power of the power amplifier 6 increases. . As a result, a decrease in output power due to a sudden temperature increase of the power amplifier 6 is corrected, and the information readable distance of the RFID tag can be prevented from being shortened. In addition, since it is not necessary to distribute and monitor the output of the power amplifier as in the prior art, the transmission power efficiency is unlikely to decrease.

(Operating point adjustment circuit)
FIG. 5 is a circuit diagram of the operating point adjustment circuit 21 and the power amplifier 6. The power amplifier 6 includes an FET transistor Tr2 as an amplifying element, and an RF signal output from the modulation circuit 15 via the input terminal 6b is applied to the gate of the transistor Tr2. The operating point adjustment circuit 21 includes a grounded NPN bipolar transistor Tr1 and resistors R1 to R3 that divide the collector voltage of the transistor Tr1. The resistor R1 is connected in series to the collector of the transistor Tr1, the resistors R2 and R3 are connected in series between the power supply and the ground, and the resistor R1 is connected to the connection point of the resistors R2 and R3.

The output of the transistor Tr1 is applied to the bias terminal 6a via the resistors R1 to R3. The gate voltage that is the operating point of the transistor Tr2 depends on the voltage applied to the bias terminal 6a.
When the temperature of the power amplifier 6 exceeds the threshold temperature and the output voltage of the thermistor 9 reaches the threshold voltage, the logic processing circuit 10 changes the control signal output to the operating point adjustment circuit 21 from high level to low level. .

As a result, the transistor Tr1 of the operating point adjustment circuit 21 is turned off, the voltage applied to the bias terminal 6a is increased, and the output power of the output terminal 6d of the power amplifier 6 is increased. As a result, a decrease in output power due to self-heating of the power amplifier 6 is corrected, and therefore the information readable distance is unlikely to be shortened.
Further, when the temperature of the power amplifier 6 is lower than the threshold temperature, the control signal output from the logic processing circuit 10 is at a high level, so that the transistor Tr1 of the operating point adjustment circuit 21 maintains the ON state. The gate voltage of the transistor Tr2 becomes low, and the output power of the power amplifier 6 is maintained in the state before being lowered.

  The set voltage of the bias terminal 6a when the transistor Tr1 is turned on is set to a level where the output distortion of the power amplifier 6 can be tolerated and the amplification efficiency of the transistor Tr2 is improved with respect to the output power.

[Carrier control processing]
When performing carrier sense, the CPU of the logic processing circuit 10 measures the temperature of the power amplifier 6 and controls the output of the power amplifier 6 according to the measurement result. Hereinafter, the control flow will be described with reference to the flowchart shown in FIG.

  When the trigger switch of the portable terminal 1 is turned on, the CPU of the logic processing circuit 10 starts carrier sense (step (hereinafter abbreviated as S) 1). Subsequently, the CPU measures the carrier level of the received signal and measures the temperature T of the thermistor 9 (S2). Subsequently, based on whether the carrier level detected in the previous S2 is equal to or higher than the threshold level, it is determined whether a carrier used by another mobile terminal has been detected (S3).

  If it is determined that a carrier used by another mobile terminal is detected (S3: Yes), the frequency channel (ch) is changed (S4), and S2 and S3 are executed again. That is, S2 and S3 are executed until an empty channel is found. If it is determined that the carrier used by another mobile terminal is not detected (S3: No), it is determined whether or not the temperature T of the thermistor 9 measured in S2 is equal to or higher than the threshold temperature Tth (S5). .

  If it is determined that the temperature T of the thermistor 9 is equal to or higher than the threshold temperature Tth (S5: Yes), the control signal output to the operating point adjustment circuit 21 is changed from the high level to the low level as described above. The output power of the power amplifier 6 is adjusted to increase (S6). Subsequently, a timer ta for measuring a time during which the carrier is turned on (for example, 4 seconds) is started (S7), and the carrier is turned on, that is, a transmission signal is transmitted from the microstrip antenna 4 (S8).

  Subsequently, it is determined whether or not the trigger switch remains ON (S9). If it is determined that the trigger switch remains ON (S9: Yes), the measurement time ta of the timer ta is equal to or greater than the threshold time tha. It is determined whether or not (S10). If it is determined that the measurement time ta is equal to or longer than the threshold time tas (S10: Yes), the carrier is turned off (S11), and carrier sense is started again (S1). In S9, when it is determined that the trigger switch is not kept ON (S9: No), the carrier is turned OFF (S12).

As described above, the temperature T of the thermistor 9 is measured each time carrier sense is executed, and correction control is performed so that the output power of the power amplifier 6 is increased when the measured temperature T is equal to or higher than the threshold temperature Tth. Therefore, even if the portable terminal 1 is used for a long time, it is possible to suppress a decrease in output power due to a sudden temperature rise of the power amplifier 6.
Accordingly, the information readable distance expected by the operator (operator) can be maintained.

[Effect of the embodiment]
(1) As described above, if the portable terminal 1 according to the above-described embodiment is used, the temperature of the power amplifier 6 is measured by the thermistor 9, and the power amplifier is measured when the measured temperature becomes equal to or higher than the threshold temperature. By changing the operating point 6, it is possible to increase the output of the power amplifier 6 and correct the output decrease due to the temperature increase.
Therefore, since the output of the power amplifier 6 is not distributed, the transmission power efficiency is unlikely to decrease.

(2) Moreover, since the temperature of the power amplifier 6 is measured in the processing routine for performing carrier sense, communication with the RFID tag can be started with the transmission power efficiency corrected.
Therefore, since the change in the information readable distance can be reduced, the reading operation feeling is hardly changed.

In particular, even when the portable terminal 1 is continuously used with the trigger switch turned on, the temperature of the power amplifier 6 can be measured every time carrier sense is performed.
Therefore, even when the portable terminal 1 is used continuously, the rapid temperature rise of the power amplifier 6 can be mitigated, so that the transmission power efficiency is hardly lowered and the information readable distance is hardly shortened.

(3) Of the first and second A / D conversion circuits 12 and 13 used for demodulation of the received signal, the thermistor is used by using the second A / D conversion circuit 13 which is not used at the time of carrier sense. 9 can be A / D converted, so that the manufacturing cost required for temperature measurement of the power amplifier 6 can be suppressed.

(4) Furthermore, since the heat generated from the power amplifier 6 can be transmitted to the microstrip antenna 4, a sudden temperature rise of the power amplifier 6 can be mitigated.
In particular, since the dielectric 4a constituting the microstrip antenna 4 is formed of ceramics, the heat generated from the power amplifier 6 can be radiated efficiently, so that a rapid temperature rise of the power amplifier 6 can be effectively performed. Can be relaxed.
Therefore, since the transmission power efficiency is difficult to decrease and the information readable distance is difficult to be shortened, the reading operation feeling is difficult to change.

<Other embodiments>
(1) FIG. 7 is an explanatory diagram showing a main electrical configuration of a mobile terminal according to another embodiment. A variable attenuator 24 is electrically connected between the output side of the modulation circuit 15 and the input side of the power amplifier 6. The variable attenuator 24 is electrically connected to the logic processing circuit 10. When the temperature T of the Samister 9 becomes equal to or higher than the threshold temperature Tth, the logic processing circuit 10 outputs a control signal to the variable attenuator 24, the variable attenuator 24 raises the output of the modulation circuit 15, and the input level of the power amplifier 6 is increased. As a result, the output power of the power amplifier 6 increases.
Even when this configuration is used, since the output of the power amplifier 6 is not distributed, the transmission power efficiency is hardly lowered. A portable terminal using this configuration corresponds to the invention according to claim 4.

(2) Instead of providing the operating point adjustment circuit 21, the output power level of the modulation circuit 15 is increased by increasing the level of the modulation signal output from the bandpass filter circuit 11 to the modulation circuit 15. The output power can also be increased.
Even when this configuration is used, since the output of the power amplifier 6 is not distributed, the transmission power efficiency is hardly lowered. A portable terminal using this configuration corresponds to the invention according to claim 3.

  For example, the logic processing circuit 10 stores a plurality of levels as transmission data levels to be output to the D / A conversion circuit 23 in a selectable manner, and selects a higher level when the temperature T of the thermistor 9 becomes equal to or higher than the threshold temperature Tth. By doing so, the level of transmission data is increased.

  Alternatively, the D / A conversion circuit 23 is configured so as to increase the output level of D / A conversion according to a command from the logic processing circuit 10. For example, when a plurality of loads (for example, resistance elements) that can be switched are selectively connected to the output stage of the D / A conversion circuit and the temperature T of the thermistor 9 becomes equal to or higher than the threshold temperature Tth, the D / A A load is selected so that the output of the conversion circuit is high.

(3) FIG. 8 is an explanatory diagram of a microstrip antenna provided in a mobile terminal according to another embodiment. A power amplifier 6, a circulator 8, and a feeding point 7 provided on the back surface of the feeding circuit board 5 are covered with a shield case 40. A thermistor 9 is provided near the outside of the shield case 40. The shield case 40 is formed of a material having both electromagnetic shielding performance and heat transfer performance (for example, metal such as copper and aluminum), and the effect of the electromagnetic shielding and the heat generated from the power amplifier 6 are supplied to the thermistor 9. It has the effect of transferring heat. If this configuration is used, the thermistor 9 does not necessarily have to be arranged in the vicinity of the power amplifier 6, so that the degree of freedom in arranging the thermistor 9 can be increased.

1 .. Mobile terminal, 4 .. Microstrip antenna, 5 .. Feed circuit board,
6 .... Power amplifier, 7 .... Feeding point, 8 .... Circulator, 9 .... Thermistor,
10a ... Temperature measuring unit, 21 ... Operating point adjustment circuit.

Claims (10)

An amplification circuit that amplifies the output of the modulation circuit, and an antenna that transmits the output of the amplification circuit as a radio wave, and has a function of reading information recorded on the RFID tag by communicating with the RFID tag using the radio wave. In the mobile terminal
A temperature detecting element that outputs a signal corresponding to the temperature of the amplifier circuit;
A temperature measurement unit that measures the temperature of the amplifier circuit based on a signal output from the temperature detection element;
A control circuit for increasing the output of the amplifier circuit when the temperature measured by the temperature measurement unit is equal to or higher than a threshold;
A portable terminal characterized by comprising: The control circuit includes:
The mobile terminal according to claim 1, having at least a function of increasing an output of the amplifier circuit by changing an operating point of the amplifier circuit. The modulation circuit is an amplitude modulation circuit;
The control circuit includes:
The portable terminal according to claim 1, wherein the portable terminal has at least a function of increasing an output level of the modulation circuit by controlling a modulation signal input to the modulation circuit. The control circuit includes:
The portable terminal according to any one of claims 1 to 3, which has at least a function of increasing an output of the amplifier circuit by increasing an input level of the amplifier circuit. The temperature measuring unit is
The portable terminal according to any one of claims 1 to 4, wherein the temperature of the amplifier circuit is measured before communication with the RFID tag is started by the radio wave. The temperature measuring unit is
The portable terminal according to claim 5, wherein the temperature of the amplifier circuit is measured in a processing routine for performing carrier sense. A demodulation circuit for demodulating radio waves received from the RFID tag;
An A / D conversion circuit for A / D converting the output of the demodulation circuit,
The temperature measuring unit is
2. The signal output from the temperature detection element is A / D converted using the A / D conversion circuit, and the temperature of the amplifier circuit is measured based on the converted digital value. The portable terminal as described in any one of Claim 6 thru | or 6. The demodulation circuit includes:
An I demodulation circuit for I demodulating radio waves received from the RFID tag, and a Q demodulation circuit for Q demodulating radio waves received from the RFID tag;
The A / D conversion circuit includes:
A first A / D conversion circuit for A / D converting the output of the I demodulation circuit;
A second A / D conversion circuit for A / D converting the output of the Q demodulation circuit,
The temperature measuring unit is
The signal output from the temperature detection element is A / D converted using one of the first and second A / D conversion circuits, and the temperature of the amplifier circuit is measured based on the converted digital value. The mobile terminal according to claim 7. The antenna is a microstrip antenna;
The portable terminal according to any one of claims 1 to 8, wherein the portable terminal is configured to transmit heat generated from the amplifier circuit to the microstrip antenna. The microstrip antenna is
A dielectric formed of ceramics;
A conductive pattern formed on the surface of the dielectric;
A circuit board integrally disposed on the back surface of the dielectric,
The portable terminal according to claim 9, wherein the amplifier circuit is disposed on the circuit board.

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