JPS59500695A - intercommunication system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] intercommunication system Technical field The present invention relates to an intercommunication system, in particular a baseband communication system to enable simultaneous calls. This paper relates to a bus system in which frequency multiplexing is performed on a bus.

Background of the invention In homes and offices, shields provide intercommunication services to many devices. There is a need. Users can send verbal messages to another person in a far away location. Its quality is that it can be communicated. If you use it in combination with a telephone, you can receive calls from external agents. This is especially useful when you need to transfer a call to another location.

Intercommunication systems are well known, but implementation always requires two or more wires. special equipment such as selection switches and separate control hardware is also often required. It is. These items tend to be cumbersome and expensive. moreover , many subdivisions do not have more than one set of wires, and one set of wires is It is common and usable in those sub-districts that are oriented to com services.

Old technology intercommunication systems are already used in other devices (perhaps telephones). Because it is necessary to use a part of the frequency spectrum (base band) that is , cannot be operated simultaneously with other such devices. modulated carrier system This system is known as an intercommunication service technology that can be used simultaneously on the same wire pair. provides the necessary frequency translation to allow

No. 3.705., filed by Nakamura et al. on December 5, 1972. In No. 412, the main station and sub station can talk simultaneously on a single wire pair. A multi-ink phone is disclosed. The frequency difference between the transmitters is the audio frequency. It uses amplitude modulated carrier waves that are larger than the number. This allows the - Eliminates interference sound in the audio band. In this device, each handset is different. Each device becomes increasingly complex as the number of terminals increases. “.

It is desirable to provide conference facilities that allow multiple parties to make calls at the same time. the Natural interactions occur in such facilities. This is an indication of understanding or consent, or This is because the absence is normally fed back. This is true of fellow interlocutors. When the faces cannot be seen and when the central words are ``epi'', ``nod'', or similar This is especially necessary when words are missing. Many older technology conferencing systems In order to speak, you have to activate a switch - the so-called "talk mode switch". -There was a need. It is not possible to detect the listener's opinion in the commotion mode. . As a result, the talkers tend to convey their messages in a rather formal manner. Ru. Informality of interaction is lost and spontaneity becomes virtually impossible.

Therefore, it is an object of the present invention to connect a pair of existing electric wires without interference of signals on the wires. The object of the present invention is to provide an intercommunication system that can be used in various ways and has many terminals.

Another object of the invention is to enable simultaneous talks between all terminals. .

Yet another object of the invention is to increase the number of terminals by identically made units. The objective is to provide an interactive communication system that allows communication between the two parties.

Summary of the invention In accordance with the object of the present invention, a frequency multiplexing system provides intercommunication services to a large number of terminals. Disclose the system. The reference frequency is distributed to each terminal using a common bus. It will be done.

At each terminal, a local oscillator generates a carrier signal that is phase-locked to a reference frequency. occurs. The carrier signal is then modulated by a locally applied input signal. and is coupled to a common bus for distribution to all terminals.

Each terminal has a receiver that detects the modulated signal on the bus. detected The signal is a linear sum of input signals provided locally from each terminal. That's it Since the same carrier wave is used in both modulators, nonlinearity is minimized and Interfering sounds in each demodulator are prevented. The benefits of this technology are amplitude modulation and phase This occurs with a variety of modulation methods, including modulation and frequency modulation. .

In the embodiment shown in the present invention, the distributed reference frequency is wavenumber) and then used as a carrier wave. Due to this, the reference frequency The wave number and modulated carrier wave can be frequency separated, which allows selection of various signals. becomes easier. Adopts frequency modulation method. That is, even if it is other In a typical intercom environment, even though a higher bandwidth is required compared to the Bandwidth is not an issue. In this example, a pair of telephone lines are used as a common bus. I used it.

In another proposed embodiment of the invention, the power line frequency of 60H2 is set as the reference frequency. When using the power distribution system (115V AC) as a common bus, Ru.

The same modulator/demodulator is used for each terminal because there is no need to distinguish between main and slave terminals. A feature of the present invention is that simultaneous calls can be made between a large number of terminals.

Another feature of the invention is that the locally supplied signal is - frequency multiplexed over a set of wires; However, in that case, something like a telephone distribution system or an electric power distribution system This means that existing electric wires can be used.

Another feature of the invention is that the frequency modulation method reduces noise and other signals present on the bus. It is important to have strong immunity.

Brief description of the drawing Other objects and features of the invention will be apparent from the following discussion and drawings.

Figure 1 shows a typical intercom terminal using a telephone cable as a common bus. Shows interconnection equipment.

FIG. 2 is a block diagram of a typical terminal in an intercommunication system according to the present invention. Ru.

FIG. 3 shows a carrier wave that can be phase-locked to a reference frequency as in accordance with the present invention. FIG. 2 is a block diagram of a generator.

FIG. 4 is a block diagram of a frequency modulation transmitter.

FIG. 5 is a block diagram of a frequency modulation receiver.

Figure 6 is a graph of amplitude versus frequency that was implemented using telephone cables as a common bus. 3 illustrates an example frequency spectrum.

Figure 7 is a graph of amplitude versus frequency, using the 60H7 power line frequency as the reference frequency. 5. Frequency spectrum of an example in which the power distribution cable is used as a common bus is illustrated.

FIG. 8 is an outline of the line filter used in the present invention.

Figure 9 shows an overview of each terminal's filter when used for standard telephone communications. It is essential.

detailed description In the embodiment of FIG. 1, a residential area with N telephones is illustrated. These electric The handset is connected to the already existing telephone cable - also referred to here as the common bus. It is connected to the. Even though telephone cables are often 4-wire, they do not disclose Only two octopus interconnect devices are required. Frequency multiplexing is the existing By effectively utilizing pulls, the present invention eliminates the need for additional wiring. This is an advantageous point. Telephones (1, 2, N) are standard for intercom use. interconnected on frequencies other than those used for standard telephone communications.

Line filter 11 prevents intercom signals from being transmitted to the local exchange. used to separate activity on the network from the telephone network. The permissible line filter is It is shown in FIG. Here the inductance (denoted as L) is 3 µm each. with a capacitance (denoted C) of 0.5 microfarads. have value. The DC resistance of this line filter is a further consideration. direct current An inductance of 1 ohm resistance is acceptable. Therefore, the line filter in Fig. 8 is Contributes approximately 4 ohms to the common bus.

An oscillator with a specific design may be used. For purposes of illustration, the output frequency is 19.2 KH It is sufficient if the signal level is −10 dBV at z.

An input filter (not shown) is included in each telephone in FIG. This fi A router is required when the phone is used for standard telephone service. This fi The purpose of the router is to separate the standard telephone signal from the intercom signal. . An acceptable filter is shown in FIG. Here each inductance (denoted by L) ) has a value of 3 millihenries. This filter allows the phone to act as an intercom. Bypassed when used. This switching method is within the scope of the present invention. It is not shown because it deviates from the above.

Figure 2 shows an intercom service for the specific purpose of providing intercom services. A block diagram shows the circuitry that must be implemented in all terminals in a communication system. end terminal 200 (indicated by i) is connected to a common bus 210 consisting of a pair of wires. I can see that it is being done. The 19.2 KHz reference frequency on bus 210 is centered It is removed by a bandpass filter 230 with a frequency of 19.2 KHz. Served. This filter is of traditional design, with a reference frequency (fr) It just needs to have a wide enough bandwidth to pass it through. Frequency fr is the signal to be modulated Therefore, for the purpose of generating a modulated carrier wave (fc”), carrier wave generation is It is connected to the generator 240. Generator 240 is phase locked to the reference frequency. Contains an oscillator that is This oscillator is twice the reference frequency (38,4KH2 ) works. Details of the generator are illustrated and will be explained more fully in connection with FIG. Will be discussed.

A carrier wave is emitted from generator 240 onto line 204.

Its frequency is related to a factor (M) times the reference frequency. This coefficient assumes a large value However, in this case, M=2. The spectrum of the carrier wave after modulation is 1 frequency multiplexed signal. Separating the frequencies of bus signals This is to simplify the design of the filter. 38.4 KHz carrier wave audio The modulation by the audio sound is based on the reference frequency of 19.2 KHz or the standard frequency below 4) G(z). Arrangements are made to avoid duplication with other telephone services.

Modulation of the carrier wave is performed by transmitter 241. In an ideal embodiment of the invention, , Frequency modulation (FM) is chosen for several reasons. FM is a modulation method A ``crude'' form of expression, very insensitive to noise. Telephone cable is a common bus When used as a unaffected by current status. When the power distribution cable is used as a common bus, Intercom signals are not affected by power line noise such as that coming from electrical appliances. commerce It is easily used as a commercially available frequency modulator and demodulator.

After all, other modulation techniques can also be used with the present invention, and generally have a narrower band than F-M. Bandwidth is not a major issue, although only bandwidth is required.

Converter 221 converts the audio sound into an electrical signal.

In this example, the converter is installed in a microphone, such as the one attached to a telephone handset. It is. The time-varying message signal m'(t) emitted from the converter 221 is It is connected to the transmitter 241 through a transmitter 243 and a filter 234. This belief The signal is also said to be the signal to be modulated.

Other message signal sources are possible, including broadcast radio and standard telephone signals. .

The message signal is processed before being used to frequency modulate the carrier wave. - In order to reproduce audio sound with high quality, the audio frequency must be transmitted in the 5 KHz band. It is desirable that The amplitude limiter 243 controls the amplitude of the message signal. , thereby effectively limiting the bandwidth of the frequency modulated signal to approximately 20 KHz. Limited. The system is therefore characterized as "narrowband FMJ.

It provides better performance than amplitude modulation schemes and can be used for double sideband AM at 10 KHz. ), while retaining the advantages inherent in frequency modulation schemes. Amplitude limiter 243 is a traditional logarithmic amplification control circuit that strictly limits the maximum signal amplitude. centre By placing a filter 243, harmonic components generated in the amplitude limiting process are removed. That was noted.

The modulated carrier wave m (fc) is the output signal from the transmitter 241 and is transmitted through the line 202. is connected to filter 231 by. Filter 231 is a modulated carrier wave The modulated signal after removing undesired frequency components from the common path 210 and interconnect. The filter 231 is a band pass type, and the center frequency is fc.

The receiving part of telephone 200 is converted into filters 232 and 233 and receiver 242. 222. Filter 232 is similar to filter 231. Ru. , is a band-pass type, and the center frequency is fc. phone transmission It should be pointed out that sidetone is produced when the transmitter and receiver operate at the same frequency.

The phone level is not a serious problem as long as it is within the range of your own sound level do not have. Filter 232 transmits only frequencies within a predetermined range to the receiver. I will. Therefore, a reference frequency of 192 KHz and a standard voltage below 4 KHz Speech signals are removed.

Receiver 242 is an FM demodulator and is shown in more detail in FIG. what tradition A typical FM demodulator is also acceptable, but a phased-loop demodulator is recommended. used in the invention. The output of the receiver 242 contains many frequency components, and the The wavenumber components are selectively passed to transducer 222 via lead 207 . Fi Router 233 is a low-pass type and removes frequency components above 5KHz. . This is a similar design to filter 234. Transducer 222 is a traditional ・It is a speaker.

Conveniently, transducers 221 and 222 are connected to the telephone handset microphone and loudspeaker. It's a loud speaker. Although not shown in any of the drawings, transducers 221 and 222 Although included in the telephone handset, a separate loudspeaker is used for alarm purposes. It can be used for.

' Figures 3, 4, and 5 show locking to the reference frequency, frequency modulation, and frequency recovery. This is a well-known phase locking technique for things like keys. Fae The basic principle of locked-loop operation is the textbook phase-locking technique (Phasel). ock Techniques), 2nd edition (Floyd M. Cardner, 19 79979 John Reilly version). Particularly referred to Chapter 9 and Chapter 10 stomach.

FIG. 3 shows an oscillator that is harmonically locked to the reference frequency fr.

(See also Figure 10.3 of the textbook already cited.) The input reference frequency fr is The signal is supplied to the phase comparator 310 through the lead wire 201. The reference frequency fr is A sine waveform of 19.2 kHz with a nominal 38.2 kHz present on lead 305. It is compared with a 4 kHz square waveform. Two signals are compared at zero crossing . If the square wave crosses zero when the polarity of the sine wave is positive, then, for example, , a negative correction signal is sent to the square wave oscillation source. And if the polarity of the sine wave is negative When the square wave crosses zero, then the positive correction signal is the square wave oscillation source. sent to. The output signal of phase comparator 310 is looped through lead wire 302. Connected to filter 320. The loop filter 320 is a low-pass filter. ) type with a cutoff frequency of approximately 100 Hz. This provides high selectivity.

(i.e., stable reference) The output signal from loop filter 320 is smoothed The magnitude and polarity of the correction signal are determined by the voltage controlled oscillator (VCO) 330. Adjust the frequency. The output signal from the VCQ is a 25kHz square wave, which is The modulator of FIG. 4 on lead 204 and the frequency divider 340 on lead 304. It is connected to the. The frequency divider 34tl is a circuit that reduces the input frequency by a coefficient M. be. By the way, the frequency divider in M-2 is a simple binary state (flip-flop). Ru. The feedback technique is such that divider 340 is a multiple of many rational numbers (i.e., an integer A number that can be expressed as a ratio, and can be greater than, equal to, or less than 1. ), it is possible to reduce the human power frequency. By such techniques, certain references Expands the selection of vCo frequencies that can be locked to a frequency. Transport of the third straw An acceptable circuit to implement the transmitter generator is the CD4046 manufactured by National Semiconductor Co., Ltd. Chill with type phase locked loop.

FIG. 4 shows a transmitter where the carrier wave fc on input lead 204 is frequency modulated by the message signal m(t) present on input lead 205. It will be done. A frequency modulated output signal mσφ is present on lead 202.

To easily understand the operation of the transmitter, refer to the phase-locked loop shown in Figure 3. Note that it is virtually the same as the The message signal m(t) also becomes zero. Assume a moment when Phase comparator 410, loop filter 420 and VCO 4'3 0 and are interconnected as a phase-locked loop, where the lead The output on lead wire 406 is the input signal fc present on lead wire 204. is locked. The loop filter 420 is a low-pass type with approximately 1 It has a cut-off frequency of 00 Hz. This frequency is the lowest frequency component in the modulated signal. Choose low. The smoothed correction signal is changed with an upper limit frequency of 100 Hz. move. The adder 440 combines the smoothed correction signal with the message signal m(t). Together, they create a net signal that adjusts the frequency of vco43o. smoothing When viewed over a long period of time, the corrected signal has the value of the carrier wave frequency fc as the center frequency. and maintain it. The frequency change of the VCO in a short time is caused by the modulation signal m(t). controlled by An acceptable circuit to implement the modulator in Figure 4 is National Semiconductor. It is a phase-locked loop of the LM565 type made by Kyodo.

FIG. 5 shows an FM demodulator in which the frequency present on input lead 203 is A numerically modulated input signal is processed by converting frequency changes into voltage changes. It will be done.

This voltage change is present on the output lead 206.

The operation of the FM demodulator consists of two parts interconnected as a phase-locked loop. The basic structure consists of a phase comparator 510, a loop filter 520, and a VCO 530. This can be understood by thinking about the circuit again. V C0,530 is the input on the lead wire 203 It is tuned to track the instantaneous frequency of the incoming frequency modulated signal. rank The output signal from the phase comparator therefore represents the frequency difference between the incoming signal and the VCO signal. The voltage will give the magnitude and polarity as shown.

Therefore, this voltage is nothing but the signal being modulated, and it is exactly the demodulator. This is the ideal output.

In the present invention, an audio signal is used as the signal to be modulated. Therefore, the rule filter 520 is a traditional filter with an upper cutoff frequency sufficient for the transmission of voice band communications. It is a low pass filter. Here, the cutoff frequency is approximately 5 kHz z. The frequency demodulated output signal present on lead 206 essentially the various messages from all the terminals in the intercommunication system. is the linear sum of the wave signals. There are no acceptable circuits to implement the demodulator of Figure 5. It is a phase-locked loop made by National Semiconductor Cooperation.

Note that optimal operation occurs when each modulated signal is of equal amplitude. This is what can be obtained. If the amplitudes of the various modulated signals are different, distortion will occur during the demodulation process. arise. This distortion increases as the amplitude difference between the modulated signals increases. . In order for the demodulator to reproduce the linear sum of all message signals without distortion, a certain parameters are required to be equal at each terminal. I don't care about that The actual intercom system must be operated even with some degree of deterioration. Can be done. For example, if frequency locking is used as a substitute for phase locking, For example, interference sound and fluctuations in the signal level occur in the receiver. The losses incurred are considerable The extent of this depends on the modulation method selected. Phase locking is frequency locking It is preferred that such circuits are widely available and inexpensive. This is clearly a good choice.

Even in the case of a phase-locked loop, it is possible to have a loss comparable to that of the older brother.

Compare amplitude modulation systems and angle modulation systems when there are carriers with different phases. That's interesting. For simplicity, only two terminals are transmitting at the same time.

Amplitude modulation (AM) In the AM system, 5i (t) - Aimi (t) cos (μit + θi) where 5l (t) is the transmission output of the transmitter, Ai is the amplitude of the carrier wave, ml(t) is the voice message, and μm is the carrier wave amplitude. The angular frequency of the transmitted wave, θ1, is the phase angle of the carrier wave.

The message signal m1(t) is expressed as follows: ml(t) = Mi + m1ac(t) where m1ac(t) is the AC component of the first message signal , Mi represents the DC component.

Assuming ideal envelope detection, especially square law detection, the detector is AC coupled. Since the DC term is flocked, the signal and distortion components can be written as follows.

SD(,t,)-[:2AFMl+2A2M2 cos(θbiθ2.))mi ac(t)+(2AjM2+2AIM1cos(θ1-θ2))m2ac( t)dD(t)-A2m1ac(t)+AA2m1act)+2cos(θ1- θ2) [A, A2m1ac(t) m2ac(t) Look at the signal component SD(t) Then, the carrier wave phase difference (θ1-02) attenuates the output message ring. Karu. The distortion component is composed of three terms. The two square terms are harmonics specific to the square law detector. This is wave distortion. Section 3 2cos(θ1-02) [AB A2 m4 ae(i), m2ac(t ) is a term of intermodulation distortion. This term is also the result of square repetition, but co It changes directly depending on the value of s(θ1-02). Therefore, a square law detector or For a similar detector, the phase difference of the carrier components is also the attenuation of the 5message signal and It affects the output as a variation in distortion.

angle modulation The angle modulation is expressed as follows.

5i(t) = Aicos[μit+θl+φ1(t)')' - where, S; (t) is the output of the transmitter, A1 is the amplitude of the carrier wave, μl is the angular frequency of the carrier wave , θ1 is the phase angle of the carrier wave, and φ1(t) is the modulation signal. Phase modulation (PM) φ(i) − kimi(t) Here, kl is a modulation index and ml(t) is a message signal. FM system Well then The received signal is excessively amplitude limited before detection, and θ1-θ2 is limited If it is specified, the restriction can be written as follows.

If it is a PM system, the PM detector will output an output proportional to φ(1). , our interest is in φ(t). The carrier phase difference is therefore to produce a DC component. However, if the DC term is excluded, the sum of the modulated signals becomes distortion-free. The state is maintained. In the FM system, the first derivative of Φ(1) with respect to time [ I am interested in derivatives]. Therefore, if we replace φ1(t) and φ2(t), Not affected by carrier phase difference.

In each of the above systems, the transmitter frequency must be coherent. is necessary. AM systems distort and attenuate messages as a result of carrier phase differences. Suffering from decline. Phase modulation only adds a DC term after detection; FM shows the message without distortion.

The drawing in Figure 6 is a frequency domain illustration of frequency multiplexing on a two-wire telephone cable. Ru. Standard telephone service occupies frequency bands below 4 kHz. reference The frequency is 19.2 kHz, and the frequency modulated intercom signal has a center frequency of It is several 38.4 kHz.

Figure 7 is a frequency domain illustration of frequency multiplexing on a power line distribution cable. . The AC 115V signal clearly occupies a frequency of 60Hz. but However, a frequency of 60 Hz can conveniently be used as a reference frequency. I can do it. Harmonic locking is a traditional technique and is already related to Figure 3. and discussed. Large frequency with carrier frequency locked to reference frequency and harmonics The short-term stability of a 60Hz signal coupled to a frequency difference depends on the specific modulation method. This results in unacceptable results. Another reference frequency generator serves as a common bus. Regarding all power line distribution cables, 1. It is clear that it can be used.

It will be appreciated that the implementation methods discussed are merely illustrative of the principles of my invention. . In addition to this, various modifications may be made without departing from the spirit and scope of my invention. , will be brought to you by our telephone carrier.

FI6.2 Interpretation (Hz) - International flavor bait destination

Claims (1)

[Claims] 1. Transmit the reference frequency to each terminal of the intercommunication system through a pair of telephone lines, A carrier wave is generated at each terminal, Carried relative to the reference frequency so that the frequency and phase are virtually the same at each terminal. phase-lock the waves at each terminal, Modulates the carrier wave with the message signal so that it is transmitted to a pair of wires at the transmitting terminal death, Demodulating the modulated carrier wave present on a pair of wires at the receiving terminal Provides simultaneous mutual communication service between multiple terminals via a pair of electric wires. method for. 2 In an intercommunication system, a meth- od containing an oscillator for generating a carrier wave Frequency multiplexing is a device that sends the signal to a frequency multiplexed bus. means for extracting a reference frequency in response to a signal on the encoded bus; means for adjusting the frequency of the oscillator in response to a reference frequency; a means for modulating a carrier wave in response to a message signal; Means of interconnecting to multiplexed buses A device characterized by: 3. In the device according to claim 2, the modulated carrier wave is further demodulated. means for modulating the frequency of the carrier wave and the frequency of the modulated carrier signal on the frequency multiplexed bus. means for interconnecting to the demodulator within the range and and means for converting the demodulated signal into audio sound. Equipment including. 4. In the device according to claim 2, the means for adjusting is based on the rational frequency of the reference frequency. Contains a phase-locked loop to lock the carrier frequency to a multiple of That's what I do A device featuring: 5. In the apparatus according to claim 3, the means for modulating and the means for demodulating are Phase-locked circuits interconnected to provide wavenumber modulation and frequency demodulation. Contains a loop Patent featuring