JPH048660Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a variable frequency oscillator that can oscillate oscillation signals of different frequencies at different times.

(b) Prior art In a wireless telephone that enables telephone calls by transmitting and receiving signals wirelessly between a base unit connected to a telephone line and a portable handset, the handset is connected to the base unit and the handset is portable. A pilot signal is used to start the system. This pilot signal has a different frequency for each radio telephone, so that the base unit cannot be activated from any handset other than the designated handset. However, since the pilot signal needs to be transmitted at all times even during a call, Since it is not possible to use frequencies within the band, and there is an upper frequency limit due to modulation, the frequency of the pilot signal of each wireless telephone is limited, so the frequency of the pilot signal is approximated. .
Therefore, a problem arises in which a telephone call is stolen by activating the base unit from a slave unit other than the designated slave unit. Therefore, as the applicant has previously invented and applied for a patent, the first device, which has different frequencies at different times than the slave device,
When the second pilot signal is transmitted and the base unit receives the first pilot signal that is the same as the predetermined first frequency, it first puts the pilot signal comparison circuit in a standby state, and then transmits the predetermined second frequency. It is conceivable that when a second pilot signal identical to that of the second pilot signal is received, the pilot signal comparison circuit is activated and the base unit is put into an operational state to prevent theft.

(c) Purpose of the invention This invention aims to prevent theft of the wireless telephone.
This invention provides a variable frequency oscillation circuit for generating two types of pilot signals having different frequencies to be transmitted from a slave unit.

(d) Structure of the invention The present invention connects a feedback circuit consisting of a capacitor and a resistor between the base and collector of a transistor, and positively feeds back a signal from the collector to the base to cause oscillation. A capacitor is connected, and the additional resistor or additional capacitor is activated or deactivated by a switching element that is temporarily turned on or off when the power is turned on, and is caused to oscillate at one frequency ₁ for a while when the power is turned on, and then at a frequency ₂ different from the above. The present invention relates to a variable frequency oscillation circuit characterized by oscillation.

(E) Embodiment The variable frequency oscillation circuit of the present invention will be explained with reference to FIG. 1 is a transistor, and a feedback circuit 7 consisting of capacitors 2, 3, 4, resistors 5, 6, etc. is connected between the collector and base. 8 is an additional resistor connected in parallel to the resistor 5 via the transistor 9; 10 is a thyristor for controlling the transistor 9; the gate electrode is connected between the resistors 12 and 13 connected in series to the capacitor 11; There is. One end of the capacitor 11 is connected to the power supply +Vcc via a power switch 14, and the other end is connected to the power supply +Vcc via a diode 15.

The variable frequency oscillation circuit of the present invention has the above-mentioned configuration, and when the power switch 14 is turned on, the signal generated at the collector of the transistor 1 is positively fed back to the base via the feedback circuit 7, and the positive feedback signal is The signal is amplified by the transistor 1, generates a signal again at the collector, and is fed back to the base via the feedback circuit 7. Oscillation is performed by repeating this operation.

By the way, when the power switch 14 is turned off, a diode 15 is connected across the capacitor 11.
It is charged to the power supply voltage +Vcc through. Therefore, when the power switch 14 is turned on, the capacitor 1
A voltage of +2Vcc will be applied to both ends of 1,
Since the anode and gate of the thyristor 10 are reverse biased, the thyristor 10 is turned off. Therefore, since the transistor 9 is turned off, the additional resistor 8 does not contribute to the feedback circuit 7 and the oscillator has a frequency _{of 1.}
oscillates. As time passes and the charge in the capacitor 11 is discharged through the resistors 12 and 13, a forward bias is applied between the anode and the gate of the thyristor 10, and the thyristor 10 is turned on. Then, a voltage is applied to the base of the transistor 9 and the transistor 9 is turned on, so that the additional resistor 8 is connected to the feedback circuit 7. Therefore, the size of the feedback circuit 7 changes and the oscillator oscillates at a frequency ₂ different from that described above.
These oscillation signals are taken out from the output terminal 16.

Figure 2 shows the use of the variable frequency oscillation circuit of the present invention in a radio telephone, in which the pilot signal ₁ and the pilot signal generated by the variable frequency oscillation circuit are shown in FIG.
₂ is used to prevent the parent device from being started from any device other than the specified child device. molecular machine 2
0 turns on the power switch 14 to make a telephone conversation. Then, the aforementioned variable frequency oscillator 21 generates a pilot signal ₁ , which is applied to a modulation circuit ₂₂ to modulate the carrier signal. The modulated carrier wave signal is amplified by the output circuit 23, transmitted from the antenna 24, and received by the antenna 26 of the base unit 25. The received carrier wave signal is frequency-converted and detected in the main circuit 27, and then converted into an audio signal and supplied to the telephone line closing circuit 28, but at this time, the telephone line closing circuit 28 is not closed. Therefore, it cannot be added to the telephone line 29. On the other hand, the pilot signal ₁ contained in the audio signal is extracted by a filter (not shown) and applied to a phase comparator 30. If the frequency of the pilot signal ₁ is the same as the frequency of the comparison signal being oscillated from the comparison signal oscillator 31 at that time, the phase comparator 30 produces an output signal. The output signal is passed through low pass filter 3
After being amplified, the signal is applied to the amplifier 33 through the amplifier 2, and after being amplified, it is supplied to the flip-flop 34, causing the flip-flop 34 to go from an inactive state to a standby state.
The output signal of the amplifier 33 is transmitted to the comparison signal oscillator 31
is added to change the oscillation frequency of the comparison signal oscillator 31. On the other hand, the oscillation frequency of the variable frequency oscillator 21 of the slave unit changes to generate the pilot signal ₂ .
The pilot signal ₂ is sent to the modulation circuit 22 as described above.
The carrier wave signal is modulated and transmitted from the antenna 24. The carrier wave signal is converted into an audio signal in the main circuit 27 of the base unit in the same manner as described above.
Pilot signal ₂ included in that audio signal
is applied to the phase comparator 30 via a filter. At this time, a comparison signal of a different frequency from the comparison signal oscillator 31 is applied to the phase comparator 30, and if the frequency of the pilot signal ₂ matches the frequency of the comparison signal at this time, the phase comparator 30 produces an output signal. The output signal is applied to flip-flop 34 through low-pass filter 32 and amplifier 33, and inverts flip-flop 34, which has been in a standby state until now. The signal produced by flip-flop 34 thereby closes telephone line closing circuit 28. Therefore, when a dial pulse signal is transmitted from the slave unit, it is transmitted to the other party via the base unit, and the other party is called. When the other party picks up the handset and turns on the handset, the call is activated. When the other party speaks into the microphone 35 , the signal is amplified by the amplifier 36 and then transmitted to the base unit 25 , where it is modulated by the modulation circuit 32 . , and is demodulated into a voice signal in the same manner as described above and transmitted to the other party via the telephone line connection circuit 28. The message from the other party is sent to the transmitter 37 through the telephone line closing circuit 28.
and transmitted from the modulation antenna 38.
The transmitted signal is received by the antenna 39 of the handset 20, then demodulated by the receiver 40, and the speaker 41 is sounded. In this way, only the designated handset 20 can make a telephone conversation with the other party via the base unit 25.

(f) Effects of the invention As mentioned above, the variable frequency oscillation circuit of the invention has the following effects:
An additional resistor or an additional capacitor is connected to the positive feedback circuit of the oscillation circuit, the collector and emitter of a switching transistor are connected between both ends of the additional resistor or additional capacitor, and a thyristor is connected to the base of the switching transistor. However, since the thyristor is switched to a state different from the normal state until the charging/discharging capacitor is charged when the power is turned on, the thyristor is switched to a state different from the normal state immediately after the power is turned on and when the switching transistor is turned on or off. The oscillation frequency of the oscillation circuit can be made different depending on the state. Therefore, oscillation signals with different frequencies can be easily obtained.
It is suitable as a pilot signal oscillator for wireless telephones.

[Brief explanation of the drawing]

Figure 1 is a frequency variable oscillation circuit diagram of the present invention, Figure 2
The figure is a block diagram of a wireless telephone using the variable frequency oscillation circuit of the present invention. 7... Feedback circuit, 8... Additional resistor, 10... Thyristor, 14... Power switch.

Claims (1)

[Scope of utility model registration request] An oscillation transistor has a positive feedback circuit made up of a capacitor and a resistor connected between its base and collector, and the switching transistor is connected in parallel to the resistor or capacitor constituting the positive feedback circuit when it is turned on. An additional resistor or an additional capacitor that changes the oscillation frequency of the oscillation transistor from a first frequency to a second frequency, and a cathode connected to the base of the switching transistor, and an anode connected to a power supply via a power switch. a thyristor that turns on the switching transistor when the transistor is connected to the thyristor; a diode having a cathode connected to the gate of the thyristor and an anode connected to a power supply; and a cathode of the diode and the power supply; The charge/discharge capacitor is connected between the power switch and the power switch and is charged by the current supplied through the diode when the power switch is in the off state. When the thyristor is turned off by applying a reverse bias voltage to the gate of the thyristor for a predetermined period of time by inverting the charging voltage of the capacitor, the switching transistor is turned off during the oscillation operation. The transistor is oscillated at a first frequency, and after a predetermined time, a bias voltage is applied to the gate of the thyristor via the diode to turn on the thyristor, thereby turning on the switching transistor by turning on the thyristor. A variable frequency oscillation circuit characterized in that the oscillation transistor is caused to oscillate at a second frequency depending on the state.