JPH05316244A - Digital line for cordless phone - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an S/N due to the intrusion of a higher harmonic noise into a voice signal on an analog line by inserting an LPF respectively into the neighborhood of the MODEM side, and the neighborhood of the digital circuit side in a digital line. CONSTITUTION:LPF 11 and 12 inserted respectively into the neighborhood of a connecting part with a MODEM 2, and the neighborhood of the connecting part with the digital circuit, in a digital line 4, absorb the higher harmonic noise generated due to data or a clock signal in the MODEM 2 or the digital circuit. Therefore, the higher harmonic noise can be prevented from being transmitted through the LPF11 and 12 to the line 4, and easily intruding into the voice signal on an analog line 6. Thus, the intrusion of the higher harmonic noise on the line 4 arranged so as to be relatively long can be prevented, so that the deterioration of the S/N due to the intrusion of the higher harmonic noise into the voice signal on the line 6 can be prevented. Also, it is desired that the MODEM 2 is the MSK MODEM, and the digital circuit is a computer device 5 including a CPU.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cordless phone and a digital line for connecting a modem and a digital circuit for transmitting and receiving digital signals.

[0002]

2. Description of the Related Art For example, in a receiving circuit of a cordless phone,
As shown in FIG. 4, the high frequency signal received by the antenna 1 is input to the MSK modem 2 and the FM detection circuit 3.

The MSK modem 2 uses the MSK [Minimum Shif
t Keying] method (FFSK [Fast Frequency Shift Key
ing] system) to demodulate a digital signal modulated. The data and clock signal demodulated by the MSK modem 2 are sent to the computer device 5 having a CPU [Central Processing Unit] via the digital line 4.

Further, the FM detection circuit 3 uses the FM [Frequenc
y Modulation] is a circuit for demodulating an audio signal modulated by the method. The audio signal demodulated by the FM detection circuit 3 is sent to the amplifier 7 and the speaker 8 via the analog line 6 and reproduced.

[0005]

However, the cordless phone is an MSK modem 2 or an F which inputs the same high frequency signal.
Generally, the M detection circuit 3 is arranged on the same substrate, and the computer device 5 is arranged on a different substrate. Therefore, the digital line 4 connected to the MSK modem 2
Is close to the analog line 6 connected to the amplifier 7, etc.,
Moreover, it will be laid over a relatively long distance.
Moreover, since the data and the clock signal transmitted through the digital line 4 include many harmonics, the analog line 6 adjacent thereto is likely to be affected by noise. Further, this situation is not limited to the receiving circuit of the cordless phone, and is the same in the transmitting circuit.

Therefore, in the conventional cordless phone, since the digital line and the analog line are arranged close to each other starting from the same board, there is a problem that noise is easily mixed in the voice signal on the analog line. Was.

[0007]

In order to solve the above problems, the present invention provides a cordless phone including a modem for performing digital remodulation and an analog remodulation circuit for performing analog remodulation. It is characterized in that low-pass filters are respectively inserted near the modem side and near the digital circuit side of the digital line connecting between them.

Further, in addition to the above configuration, the present invention is characterized in that the modem is an MSK modem which performs MSK digital remodulation, and the digital circuit is a computer device including a CPU.

Further, in addition to the above structure, the present invention is characterized in that the low-pass filter is a filter in which a resistor is connected in series to a digital line and the digital line is grounded via a capacitor. ..

In addition to the above construction, the present invention is characterized in that the low-pass filter is a filter in which a coil is connected in series to a digital line and the digital line is grounded via a capacitor. ..

[0011]

In a cordless phone in which a digital circuit and an analog circuit are mixed and a digital line connecting the modem and the digital circuit is laid over a relatively long distance, the digital line and the analog circuit are capacitive and inductive. Are easily combined. Conventionally, this coupling mixes the harmonic noise on the digital line with the voice signal on the analog circuit.

However, when the low-pass filter is inserted near the input / output end of the digital line as in the above configuration, only the low-pass signal is transmitted on this digital line. Therefore, the harmonic noise generated by the data or clock signal in the modem or the digital circuit cannot pass through the low-pass filter to reach the digital line, and is less likely to be mixed in the voice signal on the analog circuit. ..

As a result, according to the present invention, the S / N of the voice signal on the analog circuit is prevented by preventing the intrusion of the harmonic noise onto the digital line which is laid relatively long.
It becomes possible to prevent the ratio from decreasing.

Generally, a small power type cordless phone is M
While an MSK modem that performs digital remodulation of the SK system is used, and a computer device is used as a digital circuit that processes the data and clock signals that are remodulated by this, the present invention is not limited to this, and other digital modulation is used. It is also possible to use schemes and other digital circuits.

Further, as the low-pass filter, there are a low-pass filter that uses a resistor and a capacitor to lower the high-frequency impedance to the digital line, and a coil and a capacitor that increases the high-frequency impedance to the digital line.

[0016]

Embodiments of the present invention will be described in detail below with reference to the drawings.

1 to 3 show an embodiment of the present invention, FIG. 1 is a block diagram of a receiving circuit of a cordless phone, FIG. 2 is a circuit diagram showing an example of an LPF, and FIG. 3 is an LPF.
It is a circuit diagram which shows the other example. The constituent elements having the same functions as those of the conventional example shown in FIG.

In this embodiment, a receiving circuit of a cordless phone will be described. This receiving circuit inputs the high frequency signal received by the antenna 1 to the MSK modem 2 and the FM detection circuit 3. The MSK modem 2 and the FM detection circuit 3 are arranged on the same substrate to input the same high frequency signal.

The FM detection circuit 3 is an analog demodulation circuit that FM demodulates a voice signal modulated by the FM system, which is a type of analog modulation system. The output of the FM detection circuit 3 is connected via an analog line 6 to an analog circuit composed of an amplifier 7 and a speaker 8 on different boards. Therefore, the audio signal demodulated by the FM detection circuit 3 is amplified by the amplifier 7 and reproduced from the speaker 8.

The MSK modem 2 is a modem [MOdulator-DE Modulato] for digitally demodulating a digital signal modulated by the MSK method, which is a kind of digital modulation method.
r]. The MSK method is a four-phase PSK [Phase Shift
By avoiding the 180 ° phase jump in the Keying method, a constant amplitude characteristic is ensured when the signal is band-limited, and FSK [Frequency Shif
This is also called the FFSK method because it corresponds to the case where the modulation index in the t Keying method is 0.5. The MSK modem 2 extracts the data and the clock signal from the high frequency signal and outputs the data by performing the MSK demodulation.

The output of the MSK modem 2 is the LPF 1
1, the digital circuit 4 and the LPF 12 are connected to a digital circuit including a computer device 5 on a different substrate. The computer device 5 includes a CPU,
ROM for data sent via digital line 4
In order to control the cordless phone by processing in accordance with the program stored in, the control is performed, for example, by collating the transmitted identification code and starting the reproduction of the audio signal by the analog circuit.

The LPF 11 is a low-pass filter inserted in the vicinity of the connection with the MSK modem 2 in the digital line 4. Also, the LPF 12 is a digital line 4
Is a low-pass filter inserted near the connection with the computer device 5 in FIG. These LPFs 11 and 12
2 is composed of a circuit in which a resistor R is connected in series to the digital line 4 and the digital line 4 is grounded via a capacitor C as shown in FIG. Also, FIG.
It is also possible to connect the coil L in series to the digital line 4 as shown in FIG. 1 and to configure the digital line 4 by a circuit grounded via the capacitor C. The cutoff frequency of these LPFs 11 and 12 is set to 2400 Hz.

The operation of the LPF 11 and LPF 12 will be described.

The digital line 4 and the analog line 6 are
They are laid over a relatively long distance from the same board on which the MSK modem 2 and the FM detection circuit 3 are arranged to different boards. Therefore, these digital lines 4
And the analog line 6 will be capacitively and inductively coupled. Conventionally, this coupling mixes the harmonic noise of the digital signal on the digital line 4 with the voice signal on the analog line 6.

When the LPFs 11 and 12 are low-pass filters using a resistor R and a capacitor C as shown in FIG. 2, the high-frequency component of the signals input to these LPFs 11 and 12 is the capacitor C. Since the impedance at is low, it is grounded, and only low-frequency components pass through. Therefore,
The high frequency impedance from the MSK modem 2 and the computer device 5 to the digital line 4 side becomes low, and the harmonic noise is absorbed by these LPFs 11 and 12, and does not enter the digital line 4.

Further, when the LPFs 11 and 12 are low pass filters using the coil L and the capacitor C as shown in FIG. 3, the high frequency components of the signals input to these LPFs 11 and 12 are Since the impedance of the coil L is high, it is cut off, and only the low frequency component passes. Therefore, the high frequency impedance from the MSK modem 2 and the computer device 5 to the digital line 4 side becomes high, and the harmonic noise is blocked by these LPFs 11 and 12,
It does not enter the digital line 4.

As a result, according to the digital line of the cordless phone of the present embodiment, the harmonic noise generated in the MSK modem 2 and the computer device 5 cannot be transmitted over the long digital line 4, so that the analog line 6 is used.
It becomes difficult to mix in, and the adverse effect on the audio signal can be reduced. Further, the cutoff frequency of the LPFs 11 and 12 is set to 2400 Hz, and signals in the lower frequency band can pass therethrough, so that data and clock signals can be transferred from the MSK modem 2 to the computer device 5 via the digital line 4. Can be fully transmitted.

[0028]

As is apparent from the above description, according to the digital line of the cordless phone of the present invention, it is possible to prevent harmonic noise from invading the digital line which is laid for a relatively long time. It is possible to prevent the S / N ratio from being deteriorated by mixing the noise with the voice signal on the analog line.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a block diagram of a receiving circuit of a cordless phone.

FIG. 2 shows an embodiment of the present invention, in which an LPF
It is a circuit diagram which shows an example.

FIG. 3 shows an embodiment of the present invention, in which an LPF
It is a circuit diagram which shows the other example.

FIG. 4 is a block diagram of a receiving circuit of a cordless phone, showing a conventional example.

[Explanation of symbols]

 2 MSK modem 3 FM detection circuit 4 digital line 5 computer device 11 LPF 12 LPF

Claims (4)

[Claims] 1. A cordless phone equipped with a modem for performing digital remodulation and an analog remodulation circuit for performing analog remodulation, in the vicinity of the modem side and near the digital circuit side of a digital line connecting between the modem and the digital circuit. Cordless phone digital lines, each of which has a low-pass filter inserted. 2. The modem is an MSK modem that performs MSK digital remodulation, and the digital circuit is a CP.
The cordless phone digital line according to claim 1, which is a computer device including a U. 3. The cordless phone digital line according to claim 1 or 2, wherein the low-pass filter is a filter in which a resistor is connected in series to the digital line and the digital line is grounded via a capacitor. .. 4. A cordless phone digital line according to claim 1, wherein the low-pass filter is a filter in which a coil is connected in series to the digital line and the digital line is grounded via a capacitor. ..