Electronic device having an AGC loop

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.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 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 accuracy in manufacturing electronic parts, etc.
 2. Description of the Related Art
 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, a 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, Japanese Patent Unexamined Publication No. Hei 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.
 SUMMARY OF THE INVENTION
 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 setting a voltage which is compared with
 an output voltage of a battery, individually.
 Another object of the present invention is to provide a portable radio
 device which improves in 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 in
 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.
 It is preferable that 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 sets the comparison voltage.
 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 from
 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.

In the drawings, the same reference numerals denote the same structural
 elements.
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 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 through a
 switch 2. The antenna 3 is connected to a movable contact a 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 .alpha. or .beta..
 A directional coupler 4 branches a part of the power-amplified radio
 frequency signal and takes out it. 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 Vth stored in the
 memory 9 is set individually during production of the radio device as will
 be described later.
 A battery 12 supplies a power to the respective circuits including the AGC
 7.
 A stabilizing 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 .beta. 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 .beta. thereof during production
 of the radio device, but it is connected to the contact .alpha. 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 .beta. of the switch 2 through the RF cable 15, and the
 movable contact of the switch 2 is connected to the contact .alpha.
 thereof. Instead of the battery 12, the stabilizing 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 .beta. of the switch 2, so as to be
 power-monitored. The voltage from the stabilizing power supply is changed
 to a predetermined power Pth with which the voltage drop is to be
 announced to the user. The voltage drop preferably represents the
 condition under which the device is inoperable. A voltage Vp 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 .alpha.
 thereof.
 In an actual use, the radio frequency signal is amplified by the power
 amplifier 1, and then sent out from the antenna 3 through 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 CPU 10.
 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 axis of abscissas represents the
 supply voltage whereas the axis of ordinates on the left side represents
 the transmission power, and the axis of ordinates on the right side
 represents the output voltage of the detector.
 The power amplifier 1, in which a 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 Vfu11) which is
 sufficient to fully charge the battery 12 or to drive 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 Vth which has been measured during the production is
 stored in the memory 9, and corresponds to the power Pth with which an
 alarm is given.
 In FIG. 2, a solid line d (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 stabilizing power supply is
 supplied to the A/D convertor 8, and the voltage Vbth from the stabilizing
 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 with in the spirit and scope of the invention.