KR100237111B1 - city phone combined with wireless phon - Google Patents

Abstract

The present invention relates to a wireless telephone combined use Citi phone, and an antenna for transmitting and receiving airwave signals; A switching unit for alternately connecting the antenna and the receiver, the antenna and the transmitter, or both the antenna and the receiver and the transmitter according to a control signal; A first bandpass filter provided between the switching unit and the receiving unit to selectively pass a frequency band of the Citiphone and a reception frequency band of the home wireless telephone among the airwave signals received through the antenna according to the control signal; A second bandpass filter provided between the switching unit and the transmitting unit and selectively passing a frequency band of a Citiphone and a transmission frequency band of a home wireless telephone among the airwave signals to be transmitted through the antenna according to the control signal; And an audible frequency converter for converting a voice signal input through the voice signal input means or a signal of the radiotelephone frequency band that has passed through the second bandpass filter into a home frequency. ) Can be used as a home 900MHz wireless telephone, and the control signal CTRL1 can be deactivated and used as a Citiphone when going out.

Description

City phone combined with wireless phon}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Citiphone combined with a cordless telephone, and more particularly, to a Citiphone that can be used as a substitute for a cordless telephone by allowing incoming calls within a general home.

With the development of communication technology, the spread of portable wireless mobile communication means is rapidly made. Among such mobile communication means, mobile communication means called “city phones” are actively being used as transmission-only mobile communication means. The Citiphone is able to make outgoing calls but not receive calls, but the system has a low price and a low call charge.

1 is a block diagram showing a system configuration of such a conventional city phone.

Conventional city phones can be largely divided into the RF unit 1 and the baseband unit 19. The RF unit 1 is mainly a portion through which an airwave signal is input and output, and the baseband portion 19 is a portion through which an audio signal of an audio band is input and output.

The RF unit 1 requests a transmitter 2 for converting a voice signal transmitted through the baseband unit 19 into a form of an air wave signal, and the baseband unit 19 for an air wave signal received through the antenna 4. And a frequency synthesizer 15 for generating a variable frequency signal by using a receiver 3 for converting into a frequency signal of a band.

The baseband unit 19 includes a keypad 17 for inputting a telephone number and the like, an A / D and D / A converter 18 for converting an analog audio signal into a digital signal or converting a digital voice signal into an analog signal. And a coding unit 16 for encoding the signal and decoding the over-the-air signal.

The path from the conventional Citiphone configured as described above to the voice signal input through the microphone MIC in the form of an air wave signal is as follows. The analog audio signal input to the microphone MIC is converted into a digital audio signal by the A / D and D / A converter 18. The digital speech signal is encoded by the coding unit 16 and input to the transmitter 2. The modulator 9 of the transmitter 2 inserts and outputs a digital audio signal into a carrier signal of several MHz band.

However, since the output frequency band required by the Citiphone is 864.1∼868.1MHz, which is much higher than this, the mixer 8 receives a frequency signal of several MHz band output from the modulator 9 and a predetermined variable frequency signal output from the frequency synthesizer 15. After mixing, a signal having a high frequency of about 1 kHz is produced, and then the bandpass filter 7 is used to filter out only frequencies in the 864.1 to 868.1 MHz band. Citiphone outputs a signal of about 100 kHz with one of these frequency bands as a carrier frequency. At this time, the output signal of the bandpass filter 7 is amplified by about 10 kHz by the power amplifier 6 to produce an antenna (4). Propagates as airwaves through

On the contrary, the path from the aerial signal received through the antenna 4 to the audio signal is as follows.

First, the air wave signal received at the antenna 4 is reduced through the low noise amplifier 10. The band pass filter 11 filters out only frequencies in the bands 864.1 to 868.1 MHz among the output signals of the low noise amplifier 10 and outputs them to the mixer 12. However, since the frequency of the signal of this frequency band is too high to be processed by the baseband unit 19, the frequency of the signal input to the mixer 12 is lowered by the frequency synthesizer 15 to several MHz. The output signal of the mixer 12 has a constant gain through the automatic gain control stage 13 and is output to the demodulator 14. The demodulator 14 detects only the audio signal wave inserted in the carrier and outputs it to the coding unit 16. The coding unit 16 decodes the signal output from the demodulator 14 and outputs it to the A / D-D / A converter 18. The A / D and D / A converter 18 converts the decoded signal into an analog signal to drive the speaker SP.

As described above, in the Citiphone, the input and output of the airwave signal are performed by one frequency. In other words, both the input and output of the airwave signal are allocated to one of the bands 864.1∼868.1MHz. As such, a time division duplexer (TDD) is used to simultaneously perform input and output using one frequency. That is, by alternately connecting the antenna 4 and the transceiver 2, the antenna 4 and the receiver 3 in units of a predetermined time (about 2 kHz), the input and the output are performed at one frequency. The switch 5 of 1 is intermittently intermittently implemented.

The reason why such a Citiphone cannot be received and only a transmission is possible is that the structure of the receiver is much more complicated than the structure of the transmitter in general in a transmission / reception system of airwaves. Therefore, in order to reduce the cost of the system is not provided with a receiving system, and to reduce the burden of call charges to transmit and receive through a single channel.

Accordingly, an object of the present invention is to enable a call-only Citiphone to be used in a general home so that it can be used as a wireless telephone.

1 is a block diagram showing a system configuration of a conventional city phone.

Figure 2 is a block diagram showing the system configuration of a combined wireless telephone Citiphone according to the present invention.

Figure 3 is a block diagram showing a bandpass filter of a combined wireless telephone Citiphone according to the present invention.

Explanation of symbols on the main parts of the drawings

1, 21: RF unit 2, 22: transmitter

3, 23: receiver 4, 24: antenna

5, 25: power amplifier 8, 12, 28, 32: mixer

10, 30: low noise amplifier 15, 25: frequency synthesizer

LO: crystal oscillator

The present invention for this purpose and the antenna for transmitting and receiving air signals; A switching unit for alternately connecting the antenna and the receiver, the antenna and the transmitter, or both the antenna and the receiver and the transmitter according to a control signal; A first bandpass filter provided between the switching unit and the receiving unit to selectively pass a frequency band of the Citiphone and a reception frequency band of the home wireless telephone among the airwave signals received through the antenna according to the control signal; A second bandpass filter provided between the switching unit and the transmitting unit and selectively passing a frequency band of a Citiphone and a transmission frequency band of a home wireless telephone among the airwave signals to be transmitted through the antenna according to the control signal; And an audible frequency converter for converting a voice signal input through the voice signal input means or a signal of the radiotelephone frequency band passed through the second band pass filter into a home frequency.

Referring to Figures 2 to 3 a preferred embodiment of the present invention made as described above are as follows. First, Figure 2 is a block diagram showing the configuration of a Citi phone that can be used as a wireless telephone according to the present invention.

The Citiphone according to the present invention shown in FIG. 2 is largely divided into an RF unit 21 and a baseband unit 39. The RF unit 21 is a portion where the input / output of the airwave signal is mainly performed, and the baseband portion 39 is the portion where the input / output of the audio signal of the audio band is performed.

First, the RF unit 21 includes a transceiver 22 for converting a voice signal transmitted through the baseband unit 39 into a form of an airwave signal, and the baseband unit 39 converting the airwave signal received through the antenna 24. And a frequency synthesizer 35 for generating a variable frequency signal by using a receiver 23 for converting into a frequency signal of a desired band and a crystal oscillator LO.

The baseband unit 39 includes a keypad 37 for inputting a telephone number and the like, an A / D and D / A conversion unit 38 for converting an analog audio signal into a digital signal or an analog audio signal into an analog signal. And a coding unit 36 for encoding the signal and decoding the over-the-air signal, and an FM block 40 for processing the FM signal when used as a wireless telephone.

The path from the Citiphone according to the present invention configured as described above to the voice signal input through the microphone (MIC) in the form of an air wave signal is as follows.

When using as a Citiphone outdoors, the analog audio signal input to the microphone MIC is converted into the digital audio signal by the A / D and D / A converter 38. The digital speech signal is encoded by the coding unit 36 and input to the transceiver 22. The modulator 29 of the transceiver 22 inserts and outputs a digital voice signal into a carrier signal of several MHz band.

However, since the input / output frequency band of the Citiphone's RF unit 21 is 864.1∼868.1 MHz, which is much higher than that, the mixer 8 uses a predetermined frequency signal output from the frequency synthesizer 15 and a frequency signal of several MHz band output from the modulator 9. The variable frequency signal is mixed to produce a signal of high frequency of about 1 kHz, and then the bandpass filter 7 filters out only the frequencies of the band 864.1∼868.1MHz.

However, when used as a cordless telephone in the home, the control signal CTRL is activated so that the analog voice signal is frequency modulated in the FM block 40 and then directly output to the mixer 28. In this case, the frequency synthesizer 35 drives the crystal oscillator LO to increase the signal input to the mixer 28 by about 1 kHz.

The output signal of the mixer 28 is input through the power amplifier 26 to the band pass filter 27. The band pass filter 27 selectively passes the frequency band of the Citiphone and the frequency band of the general home wireless telephone according to the control signal CTRL, and transmits it to the antenna 24.

On the contrary, the path from the airwave signal received through the antenna 24 to the voice signal through the speaker SP is as follows.

First, the airwave signal received by the antenna 24 selectively outputs the frequency band of the Citiphone and the frequency band of the home wireless telephone according to the logic value of the control signal CTRL during the passage of the bandpass filter 31. The output signal of the band pass filter 31 is output to the mixer 32 after the noise component is removed by the low noise amplifier 30. In this case, the frequency of the signal input to the mixer 32 is lowered to several MHz by using the frequency synthesizer 35 because the frequency is too high to be processed by the baseband unit 39 in both cases of the Citiphone and the wireless telephone.

The output signal of the mixer 32 has a constant gain through the automatic gain control stage 33 and is output to the demodulator 34 and the FM block 40. In the case of using a Citiphone, the demodulator 34 detects only the voice signal wave inserted in the carrier and outputs it to the coding unit 36. The coding unit 36 decodes the signal output from the demodulator 34 and outputs it to the A / D and D / A converter 38. The A / D and D / A converter 38 converts the decoded signal into an analog signal to drive the speaker SP.

However, when used as a wireless telephone, the control signal CTRL is activated to operate the FM block 40. In the FM block 40, the frequency of the input signal is demodulated to detect the signal, and the speaker SP is driven using the signal.

In the above description, the control signal CTRL is a signal for selecting the Citiphone and the wireless telephone. By activating the control signal CTRL1, it can be used as a cordless phone rather than a Citiphone.

The switch 25 of FIG. 2 also operates differently in the case of a Citiphone and a wireless telephone. That is, when the control signal CTRL is at the low level, the switch 25 alternately connects the antenna 24 and the transmitter 22, the antenna 24, and the receiver 23. However, when the control signal CTRL is at a high level, both the antenna 24, the transceiver 22, and the receiver 23 are connected to each other so that both the transmission frequency and the reception frequency of the wireless telephone can be transmitted and received for use as a wireless telephone. Do.

In addition, two band pass filters 27 and 31, which are provided at the transmitter 22 and the receiver 23, respectively, are actually provided with a filter portion for passing the frequency band of the Citiphone and a frequency band for the wireless telephone. It consists of a filter part, which is shown in FIG. 3.

First, the band pass filter 27 is illustrated in FIG. The bandpass filters 41 and 42 to which the output signal of the power amplifier is input are selectively activated according to the control signal CTRL. When the control signal CTRL is at the low level, the band pass filter 41 is activated to pass only the band of 4.14.1 to 862.1 MHz, which is the frequency band of the Citiphone. However, when the control signal CTRL becomes high, another band pass filter 42 is activated to pass only a frequency in the 1 MHz band centered on the transmission frequency of a typical 900 MHz radiotelephone.

The bandpass filter 31 of FIG. 3B also alternately operates according to the control signal CTRL. When the control signal CTRL is at the low level, the band pass filter 43 is activated to pass only the band of 864.1 to 868.1 MHz, which is the frequency band of the Citiphone. However, when the control signal CTRL becomes high, another bandpass filter 44 is activated to pass only a frequency in the 1 MHz band centered on the reception frequency of a typical 900 MHz radiotelephone.

Therefore, in the home, the control signal CTRL can be activated and used as a home 900 MHz wireless telephone, and the control signal CTRL1 can be deactivated and used as a Citiphone when going out.

Accordingly, the present invention has the effect of allowing the call-only Citiphone to be used as a wireless telephone by allowing an incoming call within a general home.

Claims (5)

In the outgoing-only Citi phone equipped with a receiver, a transmitter, and voice signal input / output means, An antenna for transmitting and receiving over-the-air signals; A switching unit for alternately connecting the antenna and the receiver, the antenna and the transmitter, or both the antenna and the receiver and the transmitter according to a control signal; A first bandpass filter provided between the switching unit and the receiving unit to selectively pass a frequency band of the Citiphone and a reception frequency band of the home wireless telephone among the airwave signals received through the antenna according to the control signal; A second bandpass filter provided between the switching unit and the transmitting unit and selectively passing a frequency band of a Citiphone and a transmission frequency band of a home wireless telephone among the airwave signals to be transmitted through the antenna according to the control signal; And an audible frequency converter for converting a voice signal input through said voice signal input means or a signal of said wireless telephone frequency band which has passed through said second band pass filter into a home frequency. The Citiphone combined use of claim 1, wherein the frequency band of the Citiphone is 864.1∼868.1MHz. (correction) The wireless telephone combined use Citiphone according to claim 1, which is a 1 MHz band centered on the wireless telephone transmission frequency band. (correction) The Citiphone combined use telephone set according to claim 1, which is a 1 MHz band centered on the reception frequency band of the 900 MHz or higher wireless telephone set. The citiphone of claim 1, wherein the first bandpass filter, the second bandpass filter, and the audible frequency converter are simultaneously activated when the control signal is activated.

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