JPH09200355A - Master slave interphone set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power loss by generating a transmission modulation use carrier signal from a reception signal by a master set. SOLUTION: A base band voice signal SM111 received by a terminal BBI11 connecting to an interface circuit M11 of an interphone master set M1 is compared with a sawtooth wave SM112 with a carrier frequency SM114 outputted from a sawtooth wave generating circuit M1 3 driven by an outgoing carrier clock signal SM114 outputted from a carrier signal generating circuit M14 by a comparator circuit M111 , from which a PWM signal SM113 is outputted. Then a drive signal generating circuit M112 generates drive signals SM115 -SM118 to FET elements QM111 -QM114 of each N-channel. Then in an interphone slave set S11 , a carrier clock extract circuit S111 receives a PWM signal SS111 and generates a carrier clock signal S112 with a frequency different from the outgoing carrier clock signal SM114 , it is amplified and converted into a PM signal SS113 and outputted as a transmission signal SS11 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parent-child intercom apparatus, and more particularly to a parent-child intercom apparatus which has a simple circuit structure, can be miniaturized, and can reduce power loss.

[0002]

2. Description of the Related Art Conventionally, a system configuration example shown in FIG. 3 has been proposed as a parent-child intercom system. The parent-child intercom device includes an intercom master device M ₂ and intercom slave devices S ₂₁ and S ₂₂ connected to the intercom master device M ₂ by cables LN ₂₁₁ , LN ₂₁₂ , LN ₂₂₁ , and LN ₂₂₂ .

The intercom master unit M ₂ is composed of interface circuits M ₂₁ and M ₂₂ . The interface circuits M ₂₁ and M ₂₂ are the reception amplifier circuit M ₂₁₁ and the terminator circuit.
RM ₂₁ , bandpass filter circuit M ₂₁₃ , FM demodulation circuit
It consists of M ₂₁₂ , line transformer TM ₂₁ , and capacitor CM ₂₁ . Intercom cordless handsets S ₂₁ , S ₂₂ are microphone MC,
Microphone amplifier circuit S ₂₁₃ , FM modulation circuit S ₂₁₂ , transmission amplifier circuit S ₂₁₁ , terminator circuit RS ₂₁ , volume control volume
VR ₂₁ , speaker SP ₂₁ , series regulator circuit S ₂₁₅ ,
Diode stack S ₂ 1 _4, line transformer TS _21, composed of capacitor CS _21.

In the parent-child intercom system thus configured, the baseband audio signal input to the amplifier circuit M ₂₁₁ from the terminal BBI ₂₁ connected to the interface circuit M ₂₁ of the intercom master unit M ₂ is the same as the above-mentioned amplifier. Circuit M
_From the output of ₂₁₁ , through the terminator circuit RM ₂₁ and line transformer TM ₂₁ , from terminals PML ₂₁₁ and PML ₂₁₂ to cable LN ₂₁
1, output to LN ₂₁₂ as reception signal RS ₂₁ .

The electric power supplied to the intercom slave unit S ₂₁ is the interface circuit M ₂₁ of the intercom master unit M _2.
Power supply VM _{2 of the} line transformer TM ₂₁ terminal TM ₂₁₆ , TM ₂₁₅
To the cable LN ₂₁₁ via. The other terminal TM ₂₁₇ of the line transformer is grounded to the reference potential GM ₂₁ , and the terminal TM ₂₁₈ is connected to the cable LN ₂₁₂ . The direct current path is as follows.

VM ₂ → TM ₂₁₆ → TM ₂₁₅ → PML ₂₁₁ → LN ₂₁₁ → PSL
₂₁₁ → TS ₂₁₅ → TS ₂₁₆ → S ₂₁₄ → TS ₂₁₇ → TS ₂₁₈ → PSL ₂₁₂ → LN
₂₁₂ → PML ₂₁₂ → TM ₂₁₈ → TM ₂₁₇ → GM ₂₁ Received signal RS ₂₁ is the intercom subunit S ₂₁ terminal PSL ₂₁₁ , PSL
It is input from the line transformer TS ₂₁ from the line _{212, and} is output as a received voice from the speaker SP ₂₁ via the volume adjusting volume VR ₂₁ .

Next, the transmitted voice signal received by the microphone M _C of the intercom slave S ₂₁ is a microphone amplifier circuit S _213.
The signal is amplified by the FM modulation circuit S ₂₁₂ and converted into an FM signal by the transmission amplifier circuit S ₂₁₁ , the terminator circuit RS ₂₁ , and the line transformer TS ₂₁ from the terminals PSL ₂₁₁ and PSL ₂₁₂ to the cable LN.
It is output to ₂₁₁ and LN ₂₁₂ as a transmission signal SS ₂₁ . The power taken out from the diode stack S ₂₁₄ intercom slave unit S ₂₁ is connected to power supply VS ₂ 1 of the series regulator circuit is a constant voltage at S ₂₁₅ intercom slave unit S _21.

Further, the transmission signal SS ₂₁ is taken out from the terminals PML ₂₁₁ and PML ₂₁₂ of the intercom master unit through the line transformer TM _21, and the bandpass filter circuit M ₂₁₃ removes an unnecessary frequency signal and then FM. The demodulation circuit M ₂₁₂ demodulates the baseband transmission voice signal and outputs it from the terminal BBO ₂₁ . Although the operation of the interface circuit M ₂₁ and the intercom slave S ₂₁ has been described here, the interface circuit M ₂₂ and the intercom slave S ₂₂ also operate in the same manner. Further, explanations of the channel selection control circuits of the intercom master unit and the slave unit, the switching of the communication path of the master unit, and the connection circuit are omitted.

[0009]

In the conventional parent-child intercom system, a base unit audio signal is transmitted / received via a line transformer between the slave unit and the slave unit, so that the size of the transformer becomes large. Moreover, since the power source is also DC-fed, the core of the transformer becomes large. Further isolation is not possible. Since the receiver amplifier circuit of the base unit amplifies the analog signal, heat generation due to power loss is large.

In addition, when FM modulation or the like is used in the slave unit → the master unit, a local oscillator is required. further,
It is necessary to adjust the demodulation circuit of the base unit and the carrier frequency.
The present invention has been made in order to solve such a problem. In the master unit to the slave unit, the reception signal and the power of the intercom slave unit are transmitted by PWM modulation to achieve isolation and heat generation due to power loss. And the PWM modulation signal is used to simplify the demodulation circuit of the intercom slave unit, and the polarity of the drive current of the line transformer is set to P.
It is an object of the present invention to provide a parent-child intercom device that prevents saturation of a transformer core and is downsized by switching the carrier frequency of WM modulation alternately.

Further, according to the present invention, in the slave unit → the master unit, the carrier signal for modulation of the transmission is generated from the reception signal received from the master unit to eliminate the local oscillator, eliminating the frequency adjustment, and It is an object of the present invention to provide a parent-child intercom device that uses a FET element to restore the polarity of current flowing in a transformer and can reduce power loss.

[0012]

In order to achieve this object, a parent-child intercom apparatus according to the present invention is constructed by connecting intercom slaves to respective interface circuits of the intercom master via respective cables. Each interface circuit of the intercom base unit is a carrier signal generation circuit that outputs a downlink carrier clock signal, a sawtooth wave generation circuit that outputs a sawtooth wave driven by the downlink carrier clock signal, and compares the input baseband audio signal with a sawtooth wave. And a comparator circuit that generates a PWM signal, PWM
An FET drive circuit that generates and outputs a 4-phase drive signal from a signal based on a downstream carrier clock signal. 4 FET elements controlled by a 4-phase drive signal and a reception signal are output to a cable driven by 4 FET elements. It is equipped with a main unit side line transformer.

The intercom slave device includes a slave side line transformer connected to a cable, two FET elements switched according to the polarity of a received signal input through the slave side line transformer, and two FETs. It is equipped with a loudspeaker that is driven by elements to demodulate a PWM signal and outputs a reception sound, and a series regulator circuit that can supply power to the intercom slave unit.

Further, the intercom slave unit receives the received PW.
A carrier clock extraction circuit that extracts a downlink carrier clock signal from the M signal and generates an uplink carrier clock signal different from the downlink carrier clock signal, and converts the transmission sound received by the microphone of the intercom slave unit into a modulation signal with the uplink carrier clock signal. In addition, a modulation circuit for transmitting as a transmission signal to the cable through the two FET elements and the line transformer on the slave side is provided.

Each interface circuit of the intercom master unit transmits a transmission signal of a baseband to a differential receiver circuit to which a transmission signal is input via a cable and a master side line transformer, and a modulation signal extracted via the differential receiver circuit. A demodulation circuit for converting into a speech signal and outputting it is provided. In this parent-child intercom system, each interface circuit of the intercom master unit outputs the downlink carrier clock signal sent from the carrier signal generation circuit. The sawtooth wave generation circuit is driven by the downstream carrier clock signal and outputs a sawtooth wave. The comparator circuit compares the input baseband audio signal with a sawtooth wave and generates a PWM signal. 4 FE
The T element generates and outputs a four-phase drive signal from the PWM signal according to the downstream carrier clock signal. The main unit side line transformer is driven by four FET elements and outputs a reception signal to the cable.

In the intercom slave unit, two FET elements are switched according to the polarity of the received signal input via the slave side line transformer connected to the cable. The loud speaker is driven by two FET elements and demodulates the PWM signal and outputs a reception sound. The power of the intercom slave unit is supplied by the series regulator circuit.

Further, in the intercom slave unit, the carrier clock extraction circuit generates a downlink carrier clock signal and an uplink carrier clock signal different from the downlink carrier clock signal from the received PWM signal. The transmitted sound received by the microphone of the intercom slave unit is converted into a modulated signal by the upstream carrier clock signal. The modulation circuit transmits the signal as a transmission signal to the cable through the two FET elements and the slave side line transformer.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the parent-child intercom system of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the parent-child intercom system according to the present invention has terminals PML ₁₁₁ and PML ₁₁₂ , terminals PML ₁₂₁ and PML _{122 at} interface circuits M ₁₁ and M ₁₂ of an intercom master M _1.
To LN ₁₁₁ and LN ₁₁₂ , LN ₁₂₁ and LN ₁₂₂ , and terminals PSL ₁₁₁ and PSL ₁₁₂ , and terminals PSL ₁₂₁ and PSL ₁₂₂ to connect intercom slave units S ₁₁ and S ₁₂ , respectively.

[0019] Since the interphone parent device each interface circuit M _11, M ₁₂ of M ₁ are the same circuit configuration will be described for each interface circuit M ₁₁ intercom master unit M _1. Interface circuit of intercom base unit M ₁ M ₁₁
A carrier signal generating circuit M _14, sawtooth generator circuit M ₁₃ for outputting a sawtooth wave SM ₁₁₂ is driven by the downstream carrier clock signal SM ₁₁₄ for outputting a downlink carrier clock signal SM _114, pin BB
Sawtooth wave SM of baseband audio signal SM ₁₁₁ input from I _11
112 compared to the comparator circuit M _111, by the PWM signal SM ₁₁₃ downstream carrier clock signal SM ₁₁₄ of four-phase drive signals SM ₁₁₅ to generate a PWM signal _{SM 113, SM 116, SM 117} ,
FET drive circuit M ₁₁₂ for generating and outputting SM ₁₁₈ , four N-channel FET elements controlled by four-phase drive signals
QM ₁₁₁ , QM ₁₁₂ , QM ₁₁₃ , QM ₁₁₄ , 4 N channel F
Driven by ET elements QM ₁₁₁ , QM ₁₁₂ , QM ₁₁₃ , QM ₁₁₄ , terminator circuits RM ₁₁₁ , RM ₁₁₂ to cables LN ₁₁₁ , LN ₁₁₂
And a base-side line transformer TM ₁₁ for outputting a reception signal RS ₁₁ in.

The drive signals SM ₁₁₅ , SM ₁₁₆ , SM ₁₁₇ , SM ₁₁₈ are
The FET elements QM ₁₁₁ , QM ₁₁₃ , QM ₁₁₂ , and QM ₁₁₄ are input to the gates thereof, and the power source VM ₁ is applied to the drains of the FET elements QM ₁₁₁ and QM ₁₁₃ . Source of FET element QM ₁₁₃ ,
The drain of QM ₁₁₄ is connected to the terminator circuit RM ₁₁₁ ,
The source of the FET device QM _111, the drain of the QM ₁₁₂ is connected to a terminator circuit RM _112.

The terminator circuits RM ₁₁₁ and RM ₁₁₂ are connected to the primary side terminals TM1 ₁₁ and TM ₁₁₂ of the main unit side line transformer TM ₁₁ , and the secondary side terminals TM ₁₁₃ and TM ₁₁₄ are the interface circuit M.
₁₁ terminals PML ₁₁₁ and PML ₁₁₂ are connected. Intercom slave unit S ₁₁ is switched according to the polarity of the reception signal RS ₁₁ to be input cable LN _111, connected to the LN ₁₁₂ child-side line transformer TS _11, via the handset side line transformer TS ₁₁ Two P-channel FET elements QS ₁₁₁ , QS ₁₁₂ , 2
PWM signal driven by one FET element QS ₁₁₁ , QS ₁₁₂
Loud speaker SP ₁₁ that demodulates SS ₁₁₁ and outputs a voice signal,
Power VS ₁₁ of the interphone handset S ₁₁ and a series regulator circuit S ₁₁₄ capable of supplying.

Primary side terminal TS of the line transformer TS ₁₁ on the slave side
₁₁₁ , TS ₁₁₂ are connected to the terminals PSL ₁₁₁ , PSL ₁₁₂ , and the secondary side terminals TS ₁₁₃ , TS ₁₁₅ are the drains of the FET elements QS ₁₁₁ , QS ₁₁₂ ,
Connected to the gates of the FET devices QS ₁₁₂ and QS ₁₁₁ ,
Sources of FET elements QS ₁₁₁ and QS ₁₁₂ are both capacitors CS
_It is connected to the loud speaker SP ₁₁ via _111, and the secondary side center terminal TS ₁₁₄ of the line transformer TS ₁₁ on the slave side is the loud speaker S 11.
It is connected to the reference potential GS ₁₁ of P ₁₁ .

The intercom slave S ₁₁ receives the received PWM
Extract the downlink carrier clock signal SM ₁₁₄ from the signal SS _111, downlink carrier different from the clock signal SM _114, for example a carrier clock extraction circuit for generating an uplink carrier clock signal SS ₁₁₂ of half the frequency of the downstream carrier clock signal SM ₁₁₄ S ₁₁₁ , the transmission sound SV ₁ received by the microphone MIC ₁₁ of the intercom slave S ₁₁ and amplified by the microphone amplifier circuit S ₁₁₃ is modulated by the upstream carrier clock signal SS _112.
Converted to SS _113, and through the two FET elements QS ₁₁₁ , QS ₁₁₂ and the line transformer TS ₁₁ on the slave side, cables LN ₁₁₁ , LN
PM modulation circuit S ₁₁₂ for sending as a transmission signal SS ₁₁ to _112,
And a series regulator circuit S ₁₁₄ supplies the DC power VS ₁₁ from the received PWM signal SS ₁₁₁ via the terminator circuit RS ₁ 1.

The sources of the FET elements QS ₁₁₁ and QS ₁₁₂ are both connected to the carrier clock extraction circuit S _111, and also connected to the series regulator circuit S ₁₁₄ via the terminator circuit RS ₁₁ . Microphone amplifier circuit S ₁₁₃ is a PM modulation circuit
S ₁₁₂ is connected to the sources of the FET devices QS ₁₁₁ and QS ₁₁₂ . The frequency of the upstream carrier clock signal SS ₁₁₂
Has been described as a half of the frequency of the downlink carrier clock signal SM _114, the former may be set as the frequency higher than the latter, in general, 1 / n of the former frequency latter frequency
(N is a natural number except 0 or 1).

The interface circuit M ₁₁ of the intercom base unit M ₁ includes a differential receiver circuit M 1 ₁₄ to which the transmission signal SS ₁₁ is input via the cables LN ₁₁₁ and LN ₁₁₂ and the base unit side line transformer TM ₁₁ and a differential receiver circuit M ₁₁ . A PM demodulation circuit M ₁₁₃ is provided which converts the modulated signal SM ₁₁₉ extracted via the receiver circuit M ₁₁₄ into a baseband transmission signal SM ₁₁₀ and outputs it from the terminal BBO ₁₁ .

[0026] Incidentally, the interface circuit M ₁₂ and interphone handset S ₁₂ intercom master unit M ₁ is the same as the interface circuit M ₁₁ and interphone handset S ₁₁ intercom master unit M _1. Also, the master M ₁ and the slave S ₁₁ ,
The description of the tuning control circuit of S ₁₂ and the call connection / switching circuit of the master unit are omitted. In the parent-child intercom apparatus configured in this way, as shown in FIG. 1, the terminal BBI ₁₁ connected to the interface circuit M ₁₁ of the intercom master M ₁
The baseband audio signal SM ₁₁₁ input to the sawtooth wave SM _{112 of the} carrier frequency SM ₁₁₄ output from the sawtooth wave generation circuit M ₁₃ driven by the downlink carrier clock signal SM ₁₁₄ output from the carrier signal generation circuit M ₁₄ is input. And comparator circuit M ₁₁₁
Are compared and converted into the PWM signal SM ₁₁₃ shown in FIG.

Next, the drive signal generating circuit M ₁₁₂ causes FET elements QM ₁₁₁ , QM ₁₁₂ , QM ₁₁₃ and QM _{114 of} each N channel.
Drive signals SM ₁₁₅ , SM ₁₁₆ , SM ₁₁₇ , and SM ₁₁₈ are generated and output. In FIG. 2, FET drive signals SM ₁₁₅ and SM ₁₁₆ are P
WM signal SM ₁₁₃ is output signal SM of carrier signal generation circuit M ₁₄
Output alternately in ₁₁₄ cycles. In addition, FET drive signal SM
₁₁ 7, SM ₁₁₈ is a signal obtained by each polarity reversal of the FET drive signals SM _115, SM _116.

FET drive signals SM ₁₁₅ , SM ₁₁₆ , SM ₁₁₇ , SM
The operation in the T ₂ cycle of ₁₁₈ will be described with reference to FIG. FET drive signal SM ₁₁₅ , SM ₁₁₈ is high level, FET drive signal SM
₁₁₆ and SM _{1 17} become low level, so FET element Q
The M ₁₁₁ and QM ₁₁₄ are turned on, and the FET elements QM ₁₁₃ and QM ₁₁₂ are turned off. In this state, VM ₁ → QM ₁₁₁ → RM ₁₁₂ → TM ₁₁₂ → TM ₁₁₁ → RM ₁₁₁ → QM ₁₁₄ → GM
Since current flows in the route of ₁₁ (reference potential), the cables LN ₁₁₁ and LN ₁₁₂ are routed in the route of TM ₁₁₄ → TM ₁₁₃ → LN ₁₁₁ → TS ₁₁₁ → TS ₁₁₂ → LN ₁₁₂ via the main unit side line transformer TM _11. An electric current flows. In the intercom slave unit S ₁₁ side,
FET element QS ₁₁₁ becomes the gate potential of the FET element QS ₁₁₁ is lower than the source potential is turned on current flows in the direction of the TS ₁₁₃ → TS ₁₁₄ → TS ₁₁₅ through the slave-side line transformer TS ₁ 1, SP ₁₁ → CS ₁₁₁ → QS ₁₁₁ (source) → QS ₁₁₁ (drain) → TS ₁₁₃
Current flows in the direction of → TS ₁₁₄ → GS ₁₁ .

FET drive signals SM ₁₁₅ , SM ₁₁₆ , SM ₁₁₇ , SM
The operation of the T ₃ cycle at ₁₁₈ will be described with reference to FIG. FET drive signals SM ₁₁₆ and SM ₁₁₇ are high level, FET drive signal SM
₁₁₅ , SM _{1 18} become low level, so FET element Q
The M ₁₁₃ and QM ₁₁₂ are turned on, and the FET elements QM ₁₁₁ and QM ₁₁₄ are turned off. In this state, VM ₁ → QM ₁₁₃ → RM ₁₁₁ → TM ₁₁₁ → TM ₁₁₂ → RM ₁₁₂ → QM ₁₁₂ → GM
Since current flows in the route of ₁₁ (reference potential), the cables LN ₁₁₁ and LN ₁₁₂ are routed to the route of TM ₁₁₃ → TM ₁₁₄ → LN ₁₁₂ → TS ₁₁₂ → TS ₁₁₁ → LN ₁₁₁ via the line transformer TM ₁₁ on the main unit side. An electric current flows. In the intercom slave unit S ₁₁ side,
FET element QS ₁₁₂ becomes the gate potential of the FET element QS ₁₁₂ is lower than the source potential is turned on current flows in the direction of the TS ₁₁₅ → TS ₁₁₄ → TS ₁₁₃ through the slave-side line transformer TS ₁ 1, SP ₁₁ → CS ₁₁₁ → QS ₁₁₂ (Source) → QS ₁₁₂ (Drain) → TS ₁₁₅
Current flows in the direction of → TS ₁₁₄ → GS ₁₁ . By repeating this, terminal BB
The audio signal input from I ₁₁ is multiplexed to the power supply VM ₁ , transmitted as the received signal RS ₁₁ to the cables LN ₁₁₁ and LN ₁₁₂ , received by the intercom slave S ₁₁ , and the audio signal is emitted from the loud speaker SP ₁₁ To do. In this way, by alternately switching the directions of the currents flowing in the master unit side line transformer TM ₁₁ and the slave unit side line transformer TS ₁₁ at the cycle of the downstream carrier clock signal SM ₁₁₄ , it is possible to prevent both line transformers from being saturated. There is.

In the intercom slave unit S ₁₁ , the carrier clock extraction circuit S ₁₁₁ receives the PWM signal SS ₁₁₁ received by the operation of the FET elements QS ₁₁₁ and QS ₁₁₂ and is different from the downlink carrier clock signal SM ₁₁₄ , for example, its 1 /
2, the carrier clock signal S ₁₁₂ having a period T _{4 that} is twice the period T ₁ of the downstream carrier clock signal SM ₁₁₄ is generated, and the transmission sound SV ₁ received by the microphone MIC ₁₁ is generated by the microphone amplifier circuit S ₁₁₃ . After amplification, the carrier clock signal S _112
Is converted to a PM signal SS ₁₁₃ by the PM modulation circuit S ₁₁₂ using
Through the P channel FET elements QS ₁₁₁ and QS ₁₁₂ and the cordless handset side line transformer TS1 ₁ , the signals are output from the terminals PSL ₁₁₁ and PSL ₁₁₂ to the cables LN ₁₁₁ and LN ₁₁₂ as a transmission signal SS ₁₁ . In addition, power is taken out from the series regulator circuit GS ₁₁ via the terminator circuit RS ₁₁ from the PWM signal SS ₁₁₁ , and the DC power supply VS ₁₁ of the intercom slave unit is supplied. The terminator circuit RS ₁₁ is composed of FET elements QS ₁₁₁ and QS.
It is inserted in order to increase the input impedance of the series regulator circuit as seen from ₁₁₂ and prevent the level attenuation of the PWM signal SS ₁₁₁ .

The transmission signal SS ₁₁ received via the terminals PML ₁₁₁ , PML ₁₁₂ and the main unit side line transformer TM ₁₁ at the interface circuit M ₁₁ of the intercom master unit M ₁ is taken out by the differential receiver circuit M ₁₁₄ , The PM demodulation circuit M ₁₁₃ converts it into a baseband audio signal SM ₁₁₀ and outputs it from a terminal BBO ₁₁ .
In the above example, the interface circuit of the intercom master unit is two, and the case where two intercom slave units are accommodated has been described, but the interface circuit is three or more,
The same effect is achieved when accommodating three or more intercom slaves. Further, even if a P-channel FET element is used instead of the N-channel FET element, the same effect can be obtained. However, in this case, SM ₁₁₅ , SM ₁₁₆ , SM in FIG.
_117, SM _{1 1 8} is reverse polarity.

Further, in the intercom slave, the same effect can be obtained by using the N-channel FET element instead of the P-channel FET element. However, in this case,
The connection between the source and drain terminals of QS ₁₁₁ and QS _{112 in} Figure 1 is reversed. Furthermore, the same effect can be obtained by using AM modulation instead of PM modulation. The parent-child intercom device configured in this way can also be used as an intercom exchange.

[0033]

As is apparent from the above description, according to the parent-child intercom system of the present invention, the reception signal and the power of the intercom slave are transmitted by PWM modulation from the master to the slave to achieve isolation. In addition, heat generation due to power loss can be reduced. Furthermore, the demodulation circuit of the intercom slave can be simplified by using the PWM modulation signal. Further, the polarity of the drive current of the line transformer is alternately switched by the carrier frequency of PWM modulation, so that saturation of the transformer core can be prevented and the size can be reduced.

Further, in the slave unit → the master unit, the local oscillator can be deleted by generating the carrier signal for modulating the transmission from the reception signal received from the master unit, and the frequency adjustment can be eliminated. Further, the FET element is used to restore the polarity of the current flowing through the line transformer, and the power loss can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a parent-child intercom apparatus according to the present invention.

FIG. 2 is an explanatory view explaining the operation of the parent-child intercom apparatus according to the present invention.

FIG. 3 is a circuit diagram showing a configuration of a conventional parent-child intercom device.

[Explanation of symbols]

M ₁ · · · · · · intercom master unit M _11, M ₁₂ ······ interface circuit _{LN 111, LN 112, LN 121} , LN 122 ······ cable S _11, S ₁₂ ···・ ・ ・ Intercom slave SM ₁₁₄・ ・ ・ ・ ・ ・ Down carrier clock signal M ₁₄・ ・ Carrier signal generation circuit SM ₁₁₂・ ・ Sawtooth M ₁₃・ ・ ・ ・ ・ ・ Sawtooth Generation circuit SM ₁₁₁・ ・ ・ ・ ・ ・ Baseband audio signal SM ₁₁₃・ ・ ・ ・ ・ ・ PWM signal M ₁₁₁・ ・ ・ ・ ・ ・ Comparator circuit SM ₁₁₅ , SM ₁₁₆ , SM ₁₁₇ , SM ₁₁₈・ ・ ・ ・ ・・ Four-phase drive signal M ₁₁₂・ ・ ・ ・ FET drive circuit QM ₁₁₁ , QM ₁₁₂ , QM ₁₁₃ , QM ₁₁₄・ ・ ・ ・ ・ ・ Four FET elements RS ₁₁・ ・ ・ ・ ・ Reception signal TM ₁₁・ ・ ・ ・ ・ ・ Main unit side line transformer TS ₁₁・ ・ ・ ・ ・ ・ Slave unit side line transformer QS ₁₁₁ , QS ₁₁₂・ ・ ・ ・ ・ ・ FET element RV ₁・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Received sound SP ₁₁ ... Power S ₁₁₄ of ... loudspeaker VS ₁₁ ...... interphone handset ...... series regulator SS ₁₁₂ ...... uplink carrier clock signal S ₁₁₁ ...... carrier clock Extraction circuit MIC ₁₁・ ・ ・ ・ ・ Microphone SS ₁₁₃・ ・ ・ ・ ・ Modulation signal SS ₁₁・ ・ ・ ・ ・ Sending signal S ₁₁₂・ ・ ・ ・ ・ Modulation circuit M ₁₁₄・ ・ ・ ・ ・Differential receiver circuit SM ₁₁₉・ ・ ・ ・ ・ ・ Modulation signal SM ₁₁₀・ ・ ・ ・ ・ ・ Sending signal M ₁₁₃・ ・ ・ ・ ・ ・ Demodulation circuit

Claims (2)

[Claims] 1. The cables (LN ₁₁₁ , LN ₁₁₂ , L) are connected to the interface circuits (M ₁₁ , M ₁₂ ) of the intercom master unit (M ₁ ).
N ₁₂₁ and LN ₁₂₂ ) are connected to intercom slave units (S ₁₁ and S ₁₂ ), respectively, and each interface circuit of the intercom master unit outputs a carrier signal generation circuit (SM ₁₁₄ ) that outputs a downlink carrier clock signal (SM ₁₁₄ ). M ₁₄ ), a sawtooth wave generation circuit (M ₁₃ ) driven by the downlink carrier clock signal and outputting a sawtooth wave (SM ₁₁₂ ), the input baseband audio signal (SM ₁₁₁ ) is compared with the sawtooth wave, and PWM A comparator circuit (M ₁₁₁ ) for generating a signal (SM ₁₁₃ ), a four-phase drive signal (SM ₁₁₅ , SM ₁₁₆ , from the PWM signal to the downlink carrier clock signal,
FET drive circuit (M ₁₁₂ ), which generates and outputs SM ₁₁₇ , SM ₁₁₈ ),
Four FET elements controlled by the four-phase drive signals
(QM ₁₁₁ , QM1 ₁₂ , QM ₁₁₃ , QM ₁₁₄ ), a line transformer (TM ₁₁ ) which is driven by the four FET elements and outputs a reception signal (RS ₁₁ ) to the cable, and the intercom child The machine is a line transformer (TS ₁₁ ) connected to the cable, and two FET elements (QS ₁₁₁ ) that are switched according to the polarity of the received signal input via the line transformer. , QS ₁₁₂ ), said 2
A loudspeaker (SP ₁₁ ), which is driven by a _single FET element to demodulate the PWM signal and outputs a reception sound (RV ₁ ), and a series regulator circuit (S ₁₁₄ ), which can supply the power source (VS ₁₁ ) of the intercom slave unit. A parent-child intercom device characterized by being equipped with. 2. The intercom slave unit receives the P
Extracting the downlink carrier clock signal from the WM signal,
A carrier clock extraction circuit (S ₁₁₁ ) that generates an upstream carrier clock signal (SS ₁₁₂ ) different from the downlink carrier clock signal, and a transmission sound (SV ₁ ) received by the microphone (MIC ₁₁ ) of the intercom slave unit is transmitted to the uplink. A modulation circuit (S ₁₁₂ ) for converting into a modulation signal (SS ₁₁₃ ) by a carrier clock signal and sending it as a transmission signal (SS ₁₁ ) to the cable through the two FET elements and the line transformer on the slave side is provided. The interface circuit of the intercom base unit includes a differential receiver circuit (M ₁₁₄ ) to which the transmission signal is input via the cable and the base unit side line transformer, and an extraction via the differential receiver circuit. Modulated signal (SM ₁₁₉ )
2. A demodulation circuit (M ₁₁₃ ) for converting the signal into a baseband transmission signal (SM ₁₁₀ ) and outputting the signal.
Parent-child intercom device described.