JPS61173559A - Dtmf signal generating device - Google Patents

Abstract

PURPOSE:To send out a dual-tone multiple frequency (DTMF) signal by operating a crystal oscillation circuit firstly when an operating voltage is supplied to a DTMF sender, applying an inhibit voltage to an inhibit terminal until a stable state is entered and inhibiting the transmission of the DTMF signal, and resetting the inhibit voltage after the crystal oscillation circuit enters stable operation. CONSTITUTION:When a switch 10 is turned on, the operating voltage from a power circuit is applied to the crystal oscillation circuit 3 through the switch 10, and the crystal oscillation circuit 3 oscillates. It takes a long time for the oscillation signal of the crystal oscillation circuit 3 to become stable after rising and the outputted DTMF signal A rounds, which causes a problem. For the purpose, the tone inhibit terminal 9 is connected to the power circuit through a delay circuit 12 and then even if the switch 10 is turned on, the inhibit voltage B is supplied to the inhibit terminal 9 continuously to inhibit the DTMF signal from being outputted from an output circuit 8. The inhibit terminal 9 goes up to a high level when the crystal oscillation circuit 3 becomes stable the predetermined delay time (t) of the delay circuit 12 later, thereby releasing the inhibition.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a TMF signal generator suitable as a push-button type dial signal generator used in a handset of a cordless telephone.

(b) Prior Art Push-button type dial signal generators have recently been widely used in telephones because they are easy to operate. This push-button type dial signal generator includes one that generates pulse signals corresponding to the number of pressed buttons, similar to the rotary dial signal generator.
As described in Japanese Patent No. 5-28624, there is a system that generates a multi-frequency audio frequency signal corresponding to the number of dials. It is conceivable to use the latter push-button type dial signal generator that generates multi-frequency sound signals as a handset of a cordless telephone, but in this case, it is necessary to make it into an integrated circuit and miniaturize it, so a crystal oscillation circuit is used. , the oscillation signal oscillated from the crystal oscillation circuit is frequency-divided and divided into two by a counter decoder, the divided divided signal is D/A converted to obtain a low frequency signal and a high frequency signal, and these low frequency signals and high frequency signals are The signals are combined in an output circuit to generate DTMF (Dual Tone Multiple Free-Query) (No. Ii).

By the way, when a DTMF signal generator is used as a push-button dial signal generator in a handset of a cordless telephone, it is desirable to reduce power consumption and prevent the generation of noise signals when the device is not in use except when dialing the other party. Therefore, it is desirable to stop the power supply to the crystal oscillation circuit.

(c) Problems to be solved by the invention: As mentioned above, when a DTMF signal generator is used in a push-button dial signal generator of a handset of a cordless telephone,
It is desirable to stop the power supply to the crystal oscillator circuit except when generating the dial signal, but in that case, the power is supplied to the crystal oscillator circuit to generate the dial signal, and the oscillation operation of the crystal oscillator circuit stabilizes. If you press the button too hard, the DTMF signal will become accented and you will dial incorrectly. The present invention aims to eliminate such drawbacks and relates to a DTMF signal generating device in which a DTMF signal is not generated until the crystal oscillation circuit has sufficiently started up and stabilized after power is turned on.

B) Means for Solving the Problems The DTMF signal generator of the present invention frequency-divides and separates the oscillation signal of the crystal oscillation circuit using a counter decoder, and converts each of the obtained pulse signals into a low-frequency signal. a DTMF transmitter that generates a high-frequency signal, synthesizes these low-frequency signals and high-frequency signals, and outputs a DTMF signal;
It is comprised of a power supply circuit that supplies an operating voltage to the crystal oscillation circuit and tone inhibit terminal of the transmitter, and a delay circuit connected between the tone inhibit terminal and the power supply circuit.

(E) Function The DTMF signal generator of the present invention has the above-described configuration, and when an operating voltage is supplied to the DTMF transmitter to make a call to the other party, the crystal oscillation circuit operates immediately, but the tone-in Since the inhibit terminal has a delay circuit, an inhibit voltage is supplied to it, and the DTMF signal is not output yet.

When the crystal oscillation circuit reaches a stable operating state, the inhibit voltage applied to the inhibit terminal is released and a DTMF signal is generated.

(F) Embodiment An embodiment of the DTMF signal generator of the present invention will be described with reference to the drawings. (1) is a DTMF transmitter made into an integrated circuit, and a crystal oscillator (2) is externally attached to generate an oscillation signal of a constant frequency. A crystal oscillation circuit (3) that oscillates the oscillation signal, a counter decoder (5) that frequency-divides and separates the oscillation signal according to commands from the push button device (4), and a counter decoder (5) that divides and separates the oscillation signal and takes out the oscillation signal.
A low frequency signal generation circuit (6) generates a low frequency signal by converting one digital signal taken out from 5) into an analog signal, and similarly a counter decoder (5).
), a high-frequency signal generation circuit (7) that converts the digital signal from the digital signal into an analog signal and generates a high-frequency signal, an output circuit (3) that synthesizes the low-frequency signal and the high-frequency signal and sends out a DTMF signal, and the output circuit (8) Tone inhibit terminal (9) that prohibits the transmission of DTMF signals
It becomes more. The crystal generating circuit (3) is supplied with an operating voltage from the power supply circuit through a switch, and the tone inhibit terminal (9) is supplied with an operating voltage from the power supply circuit (6) through a delay circuit. Voltage is applied.

Next, the operation of the DTMF signal generator of the present invention will be explained. When you do not need to dial, press the switch (
A) is turned off and no operating voltage is supplied to the crystal oscillator circuit (3), etc., so the crystal oscillator circuit (3) does not oscillate and may generate unnecessary oscillation signals or consume the battery of the power supply circuit unnecessarily. do not have. To call the other party now, switch (2)
), the operating voltage from the power supply circuit changes to switch (
2) to the crystal oscillation circuit (3), causing the crystal oscillation circuit (3) to oscillate.

The oscillation signal oscillated by the crystal oscillation circuit (3) is the third
As shown in the figure, it takes time to reach a stable state after rising, which is a problem with the output DTMF signal. However, in the present invention, the tone inhibit terminal (9) is connected to the power supply circuit via the delay circuit (2).
Even when the switch Q0 is turned on, the inhibit voltage (@3 B) continues to be supplied to the tone inhibit terminal (9), and the output of the DTMF signal from the output circuit (8) is prohibited. Then, the delay time (
When the crystal oscillation circuit (3) reaches a stable state after step 1) has passed, the inhibit terminal (9) becomes high level and inhibit is released, so when the push button of the push button device (4) is pressed, the pressed push button is The oscillation signal from the crystal oscillation circuit (3) is frequency-divided according to the frequency of the crystal oscillation circuit (3) to generate a pulse signal having a predetermined division ratio. The pulse signals are applied to the low frequency generator circuit (6) and the high frequency generator circuit (7), respectively.
For example, when the push button "1" is pressed, a low frequency signal of 697 Hz is obtained from the low frequency generating circuit (6), and a high frequency signal of 1209 Hz is generated from the high frequency generating circuit (7). These signals are combined in the output circuit (8) and D
It is output as a TMF signal and sent to the other party.

FIG. 2 shows an embodiment in which the DTMF signal generator of the present invention is used as a handset of a cordless telephone.

In the standby state where the receiver is waiting for a call from the other party, the selector switches (A) and (R) are switched to the state shown in the figure, and the operating voltage from the power supply circuit (2) is applied only to the receiving circuit (2). Only the receiving circuit (g) is in operation. Next, when you want to make a call to the other party from the handset, first set the selector switch to the call state located at the center contact point shown in the figure, and in addition to the receiving circuit (2), the transmitting circuit αη, the pilot oscillator (G), The DTMF transmitter (1) also has a power supply circuit (9
), the receiving circuit (to), the transmitting circuit αη, the pilot oscillator (to), and the DTMF transmitter (
1), the DTMF transmitter (1) first starts operating the crystal oscillation circuit (3) as described above, and outputs the DTMF signal after the crystal oscillation circuit (3) is in a stable state.

Therefore, when a push button of the push button device (4) is pressed, a DTMF signal having three frequencies corresponding to the number of pressed buttons is transmitted to the DTM.
It is output from the F transmitter (1). The DTMF signal is superimposed on the pilot signal of the pilot oscillator (+B), applied to the transmitting circuit α power, modulates the carrier wave into FM, and transmits it from the antenna. The transmitted carrier wave is received by the base unit, and the D
The TMF signal is demodulated and transmitted to the other party via the telephone line.

(G) Effects of the Invention As described above, the DTMF signal generator of the present invention
When the operating voltage is supplied to the MF transmitter, the crystal oscillator circuit is first operated and the DTMF signal is prohibited from being sent by supplying an inhibit voltage to the inhibit terminal until the crystal oscillator circuit is in a stable operating state. After that, the inhibit voltage is released and the DTMF signal is sent.

It is particularly suitable for battery-powered devices such as cordless telephone handsets.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a DTMF signal generator according to the present invention;
FIG. 2 is a block diagram of a cordless telephone handset using the DTMF signal generator of the present invention, and FIG. 3 is a signal waveform diagram showing the relationship between the oscillation signal of the crystal oscillation circuit and the inhibit voltage used in the present invention. . Explanation of main figure numbers (1)...DTMF transmitter, (3)...Crystal oscillation circuit, (5)...Counter decoder, (6)...
Low frequency generation circuit, (7)...High frequency generation circuit, (9
)...inhibit terminal, (6)...power supply circuit,
@...Delay circuit.

Claims (1)

[Claims] (1) The oscillation signal from the crystal oscillation circuit is divided by a counter decoder based on the command from the push button device to generate a low frequency signal and a high frequency signal, and these low frequency signals and high frequency signals are combined to generate a DTMF signal. 1. A DTMF signal generating device, characterized in that the DTMF signal generation device is inhibited from generating a DTMF signal from the DTMF transmitter until a crystal oscillation circuit is stably operated after power is turned on.