JPH024495Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field The present invention is an oscillation circuit particularly suitable for cordless telephones, and is a two-frequency signal generation circuit optimal for generating two pilot signals with different frequencies during transmission and reception. Regarding.

(b) Prior Art Generally, in a cordless telephone, a call signal is generated to the base unit on the handset side, and the handset and base unit are connected to each other in an intercom mode, which is called an intercom mode. The telephone connection state, so-called telephone (TEL) mode, is selectively switched. However, in the past, switching between the intercom mode and the telephone mode was performed by switching a manual switch provided on the base unit when the base unit received a calling signal from the slave unit.

(c) Problems to be solved by the invention As mentioned above, conventional cordless telephones were inconvenient because switching between intercom mode and telephone mode was performed using a manual switch provided on the base unit.

Therefore, it is conceivable that in the cordless telephone, pilot signals of different frequencies are used for the intercom code and the telephone mode, and the pilot signal is used to automatically switch between the intercom mode and the telephone mode.

The present invention provides a two-frequency signal generation circuit used to generate such two-frequency pilot signals.

(d) Means for Solving the Problems The two-frequency signal generation circuit of the cordless telephone of the present invention oscillates pilot signals of different frequencies from the handset, and switches the base unit to intercom mode and telephone mode using the pilot signals of different frequencies. In cordless telephones that automatically switch between
A two-frequency signal generation circuit of a slave unit that oscillates a pilot signal of a frequency different from the above is connected to a changeover switch whose movable contact piece is connected to a DC power supply and which has at least first and second contacts, and whose base is connected to a push button switch. a first switching transistor whose emitter-collector path is connected to a first contact of a changeover switch, and second and fourth switches having a bias circuit connected to a second contact of the changeover switch for supplying a bias voltage to the base. a third switching transistor whose emitter-collector path is connected to the second contact of the changeover switch and whose bias voltage is supplied via the collector-emitter of the second switching transistor; and said first or third switching transistor. It consists of an oscillation transistor whose collector is supplied with a power supply voltage through the transistor, and a plurality of capacitors and a resistor connected between the collector-base return path and the base and ground of the oscillation transistor, and between both ends of at least one of the resistors. and a time constant circuit connected to the collector and emitter of the fourth switching transistor.

(E) Function The two-frequency signal generating circuit of the cordless telephone of the present invention has the above-described configuration, and when the changeover switch is switched to the first contact and the push button is turned on, the first switching transistor is turned on, and the collector of the oscillation transistor is turned on. When a DC voltage from a DC power source is supplied through the emitter and collector of the first switching transistor, the oscillation transistor oscillates a first pilot signal having a first frequency, and the changeover switch is switched to the second contact; The second, third, and fourth switching transistors are turned on, and the DC voltage from the DC power supply is supplied to the oscillation transistor through the collector and emitter of the third switching transistor, and the time constant is set by the fourth switching transistor. By switching the time constant of the circuit, the oscillation transistor can be caused to oscillate a second pilot signal having a second frequency different from the first frequency.

(f) Embodiment An embodiment of the two-frequency signal generation circuit of the present invention will be described with reference to the drawings.

In FIG. 1, 30 is a two-frequency signal generating means, which includes a DC power source 1, a mode selector switch 2 having TALK, ON and OFF contacts, and a first switching device having a base resistor 16 connected to the base via a call button switch 3. Transistor 4, the base is
A second switching transistor 5 is connected to the junction of voltage dividing resistors 21 and 22 connected to the TALK contact, and a second switching transistor 5 whose base is connected to the collector-emitter path of said second switching transistor 5 through a series resistor 19. 3 switching transistor 6,
A fourth switching transistor 7 whose base is connected to the TALK contact via a series resistor 18, a collector whose collector is a load resistor 17, and an oscillation transistor coupled to the mode selector switch 2 via the first or third switching transistors 4, 6. 8.
A time constant circuit 9 consisting of resistors 10, 11, a variable resistor 12, and capacitors 13, 14, 15 is connected to the oscillation transistor 8, and a fourth switching transistor 7 is connected between both ends of the resistor 11.
The collector and emitter are connected.

Next, the operation of the present invention will be explained.

When the initial mode changeover switch 2 is set to the OFF position, power is not supplied to each transistor, so the oscillation transistor 8 does not oscillate and no oscillation output appears at the terminal 23.

Next, when switching to the intercom mode for intercom operation between the slave unit and the base unit, set the mode changeover switch 2 to the ON position, turn on the call button switch 3, and the first switching transistor 4 turns on, and the oscillation transistor 8
A DC voltage from the DC power supply 1 is supplied to the collector of the oscillation transistor 8, and the oscillation transistor 8 starts oscillating, and generates a first pilot signal having a first frequency _f1 from the output terminal 23. This first frequency f ₁ is determined by resistors 10 and 11, variable resistor 12, and capacitor 1.
3, 14, and 15.

The first pilot signal is supplied to a transmitting circuit 31, which FM modulates the carrier wave signal and radiates it from an antenna 32. The radiated signal from the handset is received by the antenna 40 of the base unit shown in FIG. 2, demodulated by the receiving circuit 41, detected by the pilot detection circuit 42, switches the relay 43, opens the line switching circuit 44, The base unit is disconnected from telephone lines L ₁ and L ₂ . Therefore, since the base unit is put into operation regardless of the telephone lines L ₁ and L ₂ , when you speak into the microphone 45 , it is FM modulated by the transmitting circuit 46 and sent to the antenna 4 .
It is radiated from 0. The radiated signal is received by the antenna 32 of the handset, demodulated by the receiving circuit 33, and drives the speaker 34. When the owner of the slave unit hears the message from the base unit emitted from the speaker 34 and speaks into the microphone 35, the message is FM modulated by the transmitting circuit 31 and radiated from the antenna 32. The radiated signal is transmitted to the base unit's antenna 4.
After being received at 0 and demodulated by the receiving circuit 41,
Since the speaker 47 is driven, a conversation can be held between the base unit and the slave unit.

When the call button 3 is turned off, both the dual frequency oscillation means 30 and the transmitting circuit 31 are deactivated.
The slave unit returns to standby status.

If you want to switch to the telephone mode where you can talk from the handset over the telephone line, set mode switch 2 to TALK.
Switch to Then, at point A, the DC voltage from the DC power supply 1 is supplied to voltage dividing resistors 21 and 22, and the voltage is divided by these voltage dividing resistors 21 and 22 and supplied to the base of the second switching transistor 5. When the switching transistor 5 is turned on, the third switching transistor 6 is also turned on, and a DC voltage is supplied to the oscillation transistor 8 and the transmission circuit 31. When the DC voltage is supplied, the oscillation transistor 8 oscillates, but at this time the fourth switching transistor 7 is turned on and short-circuits the resistor 11, so the time constant of the time constant circuit 9 changes and the second frequency _f2 is reached. A second pilot signal is oscillated. The second pilot signal is sent from the output terminal 23 to the transmitting circuit 3.
1, and after FM modulating the carrier wave signal, it is radiated from the antenna 32. The radiated signal is received by the antenna 40 of the base unit and demodulated by the receiving circuit 41. The second pilot signal is detected by the pilot detection circuit 42, and the relay 43 is switched to a different state from the above, the line switching circuit 44 is closed, and the base unit is closed to the telephone lines _L1 and _L2 . Therefore, a message spoken into the microphone 35 of the handset is FM-modulated on a carrier signal by the transmitting circuit 31 and radiated from the antenna 32. The radiated signal is received by the antenna 40 of the base unit, then demodulated into a message signal by the receiving circuit 41, supplied to the telephone lines L ₁ and L ₂ via the line switching circuit 44, and transmitted to the other party. A message signal from the other party is supplied from the telephone lines L ₁ and L ₂ via the line switching circuit 44 to the transmitting circuit 46, radiated from the antenna 40, and received by the antenna 32 of the handset. The received signal is demodulated by the receiving circuit 33, drives the speaker 34, and transmits a message to the owner of the handset. In this manner, a telephone call is made from the handset.

(g) Effects of the invention As described above, the two-frequency signal generation circuit of the cordless telephone of the invention switches the changeover switch to the first contact and turns on the push button switch, causing the oscillation transistor to oscillate at the first frequency, and turning the changeover switch off. By switching to the second contact, the oscillation transistor can be caused to oscillate at the second frequency. Therefore, if the present invention is used in a cordless telephone with an intercom function, as the handset is switched between intercom mode and telephone mode, First and second pilot signals having different frequencies are obtained, and the base unit can be switched to intercom mode or telephone mode using the two pilot signals, which is extremely beneficial.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a cordless telephone handset incorporating the two-frequency signal generation circuit of the present invention;
The figure is a block diagram of a master unit corresponding to the slave unit of FIG. 1. Explanation of main figure numbers, 1...DC power supply, 2...Mode selection switch, 3...Call button, 4, 5,
6, 7...first to fourth switching transistors, 8...oscillation transistor.

Claims (1)

[Scope of utility model registration request] A cordless telephone that oscillates pilot signals of different frequencies from a handset and automatically switches a base unit between an intercom mode and a telephone mode using the pilot signals of different frequencies. The two-frequency signal generating circuit 30 of the machine is connected to a changeover switch 2 whose movable contact piece is connected to a DC power source and has at least a first contact and a second contact, and whose base is connected to a push button switch 3 and whose emitter-collector path is connected to the changeover switch 2. A first switching transistor 4 is connected to the first contact of the switch 2, and second and fourth switching transistors 5, 7 are connected to the second contact of the changeover switch 2 with a bias circuit for supplying a bias voltage to the base. a third switching transistor 6 whose emitter-collector path is connected to the second contact of the changeover switch 2 and to which a bias voltage is supplied via the collector-emitter path of the second switching transistor 5; An oscillation transistor whose collector is DC-coupled to the collector-emitter path of the three switching transistors 4 and 6, and a plurality of capacitors and resistors connected between the collector-base return path and the base and ground of the oscillation transistor. The circuit comprises a time constant circuit 9 in which the collector-emitter path of a fourth switching transistor 7 is connected between both ends of at least one of the resistors, the changeover switch 2 is switched to the first contact, and the push button switch 3 is turned on. At this time, the first switching transistor 4 is turned on, and the DC voltage from the DC power supply 1 is applied to the oscillation transistor 8 via the movable piece/first contact of the changeover switch 2 and the emitter-collector path of the first switching transistor 4. When the oscillation transistor 8 oscillates the first pilot signal having the first frequency and the changeover switch 2 is switched to the second contact, the second, third and fourth switching transistors 5, 6 . 4. At least one of the resistors of the time constant circuit is short-circuited in the collector-emitter path of the switching transistor 7, the time constant of the time constant circuit is switched, and the oscillation transistor 8 has a second frequency different from the first frequency. A two-frequency signal generation circuit for a cordless telephone, characterized in that it is oscillated by a second pilot signal.