Electronic device having an AGC loop

Abstract: In a radio device, a switch 2 is disposed between a power amplifier 1 and an antenna 3, and during production of the radio device, the switch 2 is connected to a power meter 14. A battery voltage or a detection voltage corresponding to a predetermined transmission power is measured, and then stored as a comparison voltage in a memory 9. In use, the battery voltage or the detection voltage is compared with the comparison voltage, and upon detection of a low voltage, this fact is announced from a speaker 11 to a user.

Description: The present invention relates to an electronic device having an AGC loop, and more particularly to a portable radio device which compensates errors caused by in accuracy in manufacturing electronic parts, etc. Up to now, in a portable radio device such as a cordless telephone, etc., the respective circuits in the device are driven by a battery . For that reason, when a porter (user) uses the portable radio device for a long period, the battery voltage drops, thereby coming to an unusable state. To eliminate the above defect, a technique in which upon detection of the battery voltage that drops lower than a predetermined voltage, the fact that the voltage has dropped is announced to the user, has been disclosed in, for example, JP-A-4-200140. According to the disclosure in the publication, there are provided a primary battery and an auxiliary battery, and when a voltage of the primary battery drops, the battery in use is switched from the primary battery to the auxiliary battery while the fact that the voltage has dropped is announced to the user. However, in the above conventional portable radio device, a predetermined voltage is compared with an output voltage of the battery, and when the output voltage of the battery is lower than the predetermined voltage, an alarm is given to the user. Under this circumstance, for example, if a transmission power depending on the characteristic of a power amplifier is different between the respective devices, that is, if the transmission power relative to the voltage is different between the respective devices, the following problems occur because the same predetermined voltage is set in all the radio devices. There occurs such a disadvantage that in a radio device, the user is alarmed although the device is still in a communicatable state, and in another radio device, the user is not alarmed even though the communication quality is poor. Also, when the battery in use is switched from the primary battery to the auxiliary battery, the communication quality is improved in a short period. However, the provision of the auxiliary battery makes it difficult to downsize the device. US 4, 521, 912 discloses a low power indicating circuit for a radio transmitter, wherein low power for a radio transmitter is indicated by an output power detector voltage falling below a low power reference voltage derived from an existing power control circuit. The present invention has been made to solve the above problems, and therefore an object of the present invention is to provide a portable radio device which is capable of individually setting a voltage which is compared with an output voltage of a battery. Another object of the present invention is to provide a portable radio device which improves the reliability such as the transmission efficiency, the uniformity of the communication quality, etc. Still another object of the present invention is to provide a portable radio device which is capable of being downsized while improving the reliability such as the transmission efficiency, the uniformity of the communication quality, etc. In order to achieve the above objects, according to the present invention, there is provided a portable radio device which includes a power amplifier for amplifying a radio frequency signal, an antenna for sending the radio frequency signal, a switch connected between the power amplifier and the antenna, a gain controller for controlling the radio frequency signal which is sent from the antenna to a predetermined power, a converter for converting a transmission power value of the power amplifier into a voltage corresponding to the transmission voltage value, a memory in which a predetermined comparison voltage is stored, and a comparator for comparing the voltage with the comparison voltage. The switch is a three-point switch having a movable contact which is connected to one of a first contact which is connected to the antenna and a second contact which is connectable to a power meter. It is preferable that the converter includes a directional coupler for taking out a given power according to the transmission power value, and a detector for detecting said voltage according to the power from the directional coupler. Also, according to the present invention, there is provided a portable radio device which includes a converter for converting a transmission power from a power amplifier into a d.c. voltage, a memory for storing a supply voltage obtained when the transmission power becomes a predetermined power as a comparison voltage, and a circuit for comparing the d.c. voltage with the comparison voltage to generate an alarm when the d.c. voltage is lower than the comparison voltage. Further, according to the present invention, there is provided a portable radio device which includes a power amplifier for amplifying a radio frequency signal, an antenna for sending said radio frequency signal, a switch connected between the power amplifier and the antenna, a gain controller for controlling the radio frequency signal which is sent by the antenna to a predetermined power, a memory in which a predetermined voltage is stored, and a comparator for comparing a supply voltage with the voltage. It is preferable that the portable radio device further includes a notification circuit for announcing the drop of the supply voltage to a user when the comparator judges that the supply voltage is lower than the voltage. With the above structure of the present invention, the difference of a timing when the user is notified to the voltage drop between the respective devices can be eliminated. These and other objects, features and advantages of this invention will become more fully apparent from the following detailed description taken with the accompanying drawings in which: Fig. 1 is a structural block diagram showing a portable radio device according to an embodiment of the present invention; Fig. 2 is a graph representative of a relation between a transmission power and a supply voltage of the portable radio device shown in Fig. 1; and Fig. 3 is a structural block diagram showing a portable radio device according to another embodiment of the present invention. In the drawings, the same reference numerals denote the same structural elements. Now, a description will be given in more detail of preferred embodiments of the present invention with reference to the accompanying drawings. Fig. 1 is a structural block diagram showing a transmission section of a portable radio device according to an embodiment of the present invention. In Fig. 1, a power amplifier 1 power-amplifies a radio frequency signal. An antenna 3 sends the power-amplified radio frequency signal via a switch 2. The antenna 3 is connected to a movable contact α of the switch 2. The switch 2 is preferably made up of a three-point switch a movable contact of which is connected to any one of contacts α or β. A directional coupler 4 branches a part of the power-amplified radio frequency signal and takes it out. A d.c. detector 5 detects the taken-out radio frequency signal to obtain a d.c. voltage Vp. A reference voltage generator (REF) 6 generates a reference voltage, preferably, a reference voltage of 1.0V. A transmission power automatic gain control circuit (AGC) 7 compares the reference voltage with the d.c. voltage from the d.c. detector 5 to control the power amplifier 1 such that a difference between the reference voltage and the d.c. voltage becomes 0 (zero). Through an AGC loop which is made up of the directional coupler 4, the detector 5 and the AGC 7, the power amplifier 1 obtains a given output power which is preferably 30 dBm. For example, when the transmission power is 30 dBm, the d.c. detector 5 obtains the d.c. voltage of 1V. In addition, the directional coupler 4 supplies to the d.c. detector 5 a power which is coupled so as not to affect the transmission power of the directional coupler 4. An analog-to-digital (A/D) convertor 8 converts a d.c. voltage Vd from the detector 5 into a digital value, and the digital value is compared with a set voltage Vdth stored in a memory 9 in advance through a CPU 10. The CPU 10 allows a speaker 11 to be driven when the digital value is lower than the set voltage Vdth to alarm a user. The set voltage Vdth stored in the memory 9 is set individually during production of the radio device as will be described later. A battery 12 supplies power to the respective circuits including the AGC 7. A stabilized power supply 13 is used instead of the battery 12 during production of the radio device, and therefore is not provided in the radio device when the device is forwarded from a factory. A power meter 14 is used in a state where it is connected to the contact β of the switch 2 through the movable contact and an RF cable 15 during production of the radio device, and therefore is not provided in the radio device when the radio device is forwarded from the factory. Also, the movable contact of the switch 2 is connected to the contact β thereof during production of the radio device, but it is connected to the contact α when the device is forwarded from the factory. Subsequently, the operation of the portable radio device according to the present invention will be described. During production of the radio device, the power meter 14 is connected to the contact β of the switch 2 through the RF cable 15, and the movable contact of the switch 2 is connected to the contact β thereof. Instead of the battery 12, the stabilized power supply 13 supplies the power to the respective circuits. The radio frequency signal is amplified to a predetermined output power, preferably 30 dBm, through the power amplifier 1. A part of the output voltage from the power amplifier 1 is converted into a voltage Vd corresponding to the power through the directional coupler 4 and the detector 5, and the power amplifier 1 is controlled by the AGC 7 in such a manner that the output power is kept constant. The voltage Vd is converted into the digital value through the A/D convertor 8 and then supplied to the CPU 10. The output power from the power amplifier 1 is supplied to the power meter 14 through the contact β of the switch 2, so as to be power-monitored. The voltage from the stabilized power supply is changed to a predetermined power Pth at which the voltage drop is to be announced to the user. The voltage drop preferably represents the condition under which the device is no longer operable. A voltage Vp 1 from the detector 5 when the power Pth is detected by the power meter 14 is stored in the memory 9 as the comparison voltage Vdth through the CPU 10. With the above operation, the voltage corresponding to the given power is obtained for each of the radio devices, and then stored as the comparison voltage. When the production of the radio device is completed, and the radio device is forwarded from a factory, the power meter 14, the RF cable 15 and the stabilizing power supply 13 are removed from the radio device, and the movable contact of the switch 2 is connected to the contact α thereof. In an actual use, the radio frequency signal is amplified by the power amplifier 1, and then sent by the antenna 3 via the switch 2. On the other hand, a part of the amplified radio frequency signal is converted through the directional coupler 4 and the detector 5 into a d.c. voltage which is controlled so as to be made the given power by the AGC 7. Also, the output voltage Vd from the detector 5 is converted into a digital value through the A/D convertor 8, and then compared with the set voltage or comparison voltage Vdth as stored in advance in the memory 9. When the detected voltage Vd is lower than the set voltage Vdth, the speaker 11 is driven. Fig. 2 is a graph for explaining a relation between the supply voltage and the transmission power. In Fig. 2, the abscissa represents the supply voltage whereas the ordinate on the left side represents the transmission power, and the ordinate on the right side represents the output voltage of the detector. The power amplifier 1, to which power is supplied from the battery 12, is controlled so as to obtain a constant output power, for example, 30 dBm by the control of the AGC 7. There arises no problem if the AGC 7 and the power amplifier 1 are in a charged state (voltage Vref to Vfull) which is sufficient to fully charge the battery 12 or to produce the output of 30 dBm. However, when the voltage becomes lower than the voltage Vref which is sufficient to send the power of 30 dBm due to the discharge of the battery 12, the transmission power Pv is also monotonously reduced with the voltage drop of the battery 12. The way of reduction of the transmission power Pv is different depending on the individual power amplifiers as indicated by dotted lines, and in case of this embodiment, it is indicated by a solid line P1(v). The comparison voltage Vdth which has been measured during the production is stored in the memory 9, and corresponds to the power Pth at which an alarm is given. In Fig. 2, a solid line d1 (v) represents the output power voltage of the detector. Then, a portable radio device according to another embodiment of the present invention will be described with reference to Fig. 3. In Fig. 3, the same reference numerals or symbols as those in Fig. 1 have the identical meanings. For prevention of lengthy explanation, only portions different from those in Fig. 1 will be described. In Fig. 3, a voltage from the battery 12 or the stabilized power supply is supplied to the A/D convertor 8, and the voltage Vbth from the stabilized power supply when the power Pth which has been measured by the power meter 14 during the production is stored in the memory 9, and in actual use, the voltage from the battery 12 is compared with the voltage Vbth as stored. In the above-mentioned embodiments, the portable radio device was described as an example, but the present invention is applicable to communication devices, receivers or electronic devices with the power amplifier without being limited by or to those embodiments. As was described above, according to the present invention, the optimum output of the detector and the optimum set voltage such as the battery voltage, etc., with respect to the given transmission power are stored in the memory in each of the radio devices, and the user is alarmed using the optimum set voltage as stored. With this structure, a difference in the individual transmission power between the respective portable radio devices is eliminated, thereby being capable of unifying the communication quality and improving the reliability. While the invention has been described with reference to specific embodiments thereof, it will be appreciated by those skilled in the art that numerous variations, modifications, and embodiments are possible, and accordingly, all such variations, modifications, and embodiments are to be regarded as being within the scope of the invention.

Claims: An electronic device for obtaining a given output power, comprising: power amplifying means (1) for amplifying a radio frequency signal; an antenna (3) for sending said radio frequency signal; a switch (2) connected between said power amplifying means (1) and said antenna (3); gain control means for controlling said radio frequency signal which is sent by said antenna (3) to a predetermined power; converting means for converting a transmission power value of said power amplifying means (1) into a voltage corresponding to a transmission voltage value; a memory (9) for storing a predetermined comparison voltage; and comparing means (7) for comparing said voltage with said comparison voltage, wherein said switch (2) comprises a three-point switch having a first contact (α) which is connected to said antenna (3), a second contact (β) which is connectable to a power meter (14) and a movable contact which is connected to one of said first contact (α) and said second contact (β). An electronic device as claimed in claim 1, wherein said converting means comprises a directional coupler (4) for taking out a given power according to said transmission power value, and a detector (5) for detecting said voltage according to the power from said directional coupler (4). The electronic device according to claim 1 or 2, wherein said converting means is configured to convert a transmission power from said power amplifying means (1) into a d.c. voltage; said memory (9) stores a supply voltage obtained when said transmission power is equivalent to a predetermined power as a comparison voltage; and said comparing means (7) compares said d.c. voltage with said comparison voltage to generate an alarm when said d.c. voltage is lower than said comparison voltage. The electronic device according to claim 1, wherein said comparing means (7) is configured to compare a supply voltage with said comparison voltage. The electronic device as claimed in claim 4, further comprising announcing means (11) for announcing the drop of the supply voltage to a user when said comparing means (7) judges that said supply voltage is lower than said voltage. The electronic device according to any of claims 1 to 5, further comprising: means (13, 14) for predetermining a minimum supply voltage of said electronic device; and means for storing said minimum supply voltage in said memory (9) as a comparison voltage, wherein said comparison voltage may be different among individual electronic devices. The electronic device as claimed in claim 6, wherein said means for predetermining comprises a power meter (14) connected to said second contact (β) of said switch (2) and a stabilizing power supply (13) for supplying power to said electronic device. A method of setting information in an electronic device according to any of claims 1 to 7, said method comprising the steps of: setting a substantially minimum supply voltage for obtaining a predetermined transmission power; and storing one of the set substantially minimum supply voltage and a corresponding transmission power as reference information in a memory, wherein said electronic devices comprises a three point switch having a first contact which is connected to an antenna (3) of said electronic device, a second contact (β) which is connectable to a power meter (14) and a movable contact which is connected to one of said first contact (α) and said second contact (β).

Inventors: MIZOGUCHI TAMIYUKI, MIZOGUCHI, TAMIYUKI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1997
Main classification: H03G3
IPC codes: H04B1, H03G3, H04B7