CN106792352B - Side-tone eliminating circuit and two-wire full duplex intercom device using same - Google Patents
Side-tone eliminating circuit and two-wire full duplex intercom device using same Download PDFInfo
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- CN106792352B CN106792352B CN201611196681.9A CN201611196681A CN106792352B CN 106792352 B CN106792352 B CN 106792352B CN 201611196681 A CN201611196681 A CN 201611196681A CN 106792352 B CN106792352 B CN 106792352B
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- 230000030279 gene silencing Effects 0.000 claims abstract description 6
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2410/00—Microphones
- H04R2410/05—Noise reduction with a separate noise microphone
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Abstract
The invention relates to a side-tone eliminating circuit, which comprises a switch, a transformer and a silencing passage, wherein the switch can be connected with a local voice signal and takes the local voice signal as an input signal, the transformer is connected with a bus and transmits the input signal into the bus or obtains a bus audio signal from the bus, and the silencing passage is connected with the input signal and the transformer and eliminates the bus audio signal; the silencing passage comprises a differential input operational amplifier for inverting the phase of the bus audio signal and outputting a single-ended audio signal, an adder for adding the single-ended audio signal and the input signal and outputting an opposite voice signal, a digital potentiometer for adjusting the parameter of the output signal of the adder and a controller for controlling the digital potentiometer to automatically adjust the parameter. The invention also provides a two-wire full duplex intercom device which comprises the sidetone eliminating circuit. The invention can modify the circuit parameters of the side-tone eliminating part in real time, thereby realizing the clear voice talkback function under the condition of bus impedance change.
Description
Technical Field
The invention relates to a two-wire full duplex intercom device and a sidetone eliminating circuit applied to the two-wire full duplex intercom device.
Background
A two-wire full-duplex intercom device is adopted in a broadcasting system used in rail transit systems such as high-speed rails, subways and the like. The full-duplex two-wire intercom technique requires designing the sidetone canceling circuit for the bus impedance, because the bus impedance is fixed and the parameters of the sidetone canceling circuit are also fixed. However, when the impedance of the bus deviates from the standard value or changes, for example, the number of the access bus terminals changes, or the system is reconnected, the original parameters cannot be modified in time, so that the attenuation amplitude of the sound of the calling party in the receiver is affected, and the sound of the calling party and the sound of the called party cannot be heard together.
Disclosure of Invention
The invention aims to provide a sidetone canceling circuit which can automatically change parameters so as to provide clear voice when the bus impedance changes.
In order to achieve the purpose, the invention adopts the technical scheme that:
a kind of side-tone eliminating circuit, apply to two-wire full duplex intercom, the said side-tone eliminating circuit includes being able to connect with the voice signal of this party and regard it as the switch of the input signal, connect with bus and transmit the said input signal to the bus or obtain the transformer of the audio signal of the bus from the said bus, connect with said input signal and said transformer in order to carry on the silencing route of the signal cancellation to the said bus audio signal;
the noise reduction path comprises a differential input operational amplifier which inverts the bus audio signal to output a single-ended audio signal, an adder which adds the single-ended audio signal and the input signal to eliminate partial signals in the single-ended audio signal and output an opposite voice signal, a parameter adjustable digital potentiometer which is arranged between the differential input operational amplifier and the adder and adjusts the output signal of the adder, and a controller which controls the digital potentiometer to automatically adjust parameters.
Preferably, the controller includes an audio amplitude detection circuit that acquires an opposite party speech signal output by the adder and performs amplitude detection on the opposite party speech signal, and an MCU that provides a parameter adjustment reference signal to the switch as the input signal and outputs an adjustment signal according to the amplitude of the opposite party speech signal to adjust a parameter of the digital potentiometer.
Preferably, the audio amplitude detection circuit comprises a true effective value detection chip with a built-in delta sigma algorithm.
Preferably, the switch is an alternative analog switch having two input ends, namely a first input end for acquiring the local voice signal and a second input end for acquiring the parameter adjustment reference signal.
Preferably, the input signal is input to the adder via a fixed-value resistor.
Preferably, a power amplifier is disposed between the switch and the transformer, and amplifies the input signal and outputs a differential audio signal.
Preferably, a series resistor is arranged between the power amplifier and the transformer.
Preferably, the power amplifier is an AB type linear power amplifier.
Preferably, the differential input operational amplifier includes an operational amplifier, and filter capacitors are respectively connected in parallel between a non-inverting input terminal and an output terminal of the operational amplifier, and between an inverting input terminal and an output terminal of the operational amplifier.
The invention also provides a two-wire full-duplex intercom device which comprises the sidetone eliminating circuit.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the invention can modify the circuit parameters of the side-tone eliminating part in real time, thereby realizing the clear voice talkback function under the condition of bus impedance change, and being particularly suitable for a broadcasting system of rail transit.
Drawings
Fig. 1 is a schematic block diagram of the sidetone canceling circuit of the present invention.
Fig. 2 is a circuit diagram of a power amplifier in the sidetone canceling circuit of the present invention.
Fig. 3 is a circuit diagram of an adder in the sidetone canceling circuit of the present invention.
Fig. 4 is a circuit diagram of a differential input operational amplifier in the sidetone canceling circuit of the present invention.
FIG. 5 is a circuit diagram of a digital potentiometer in the sidetone canceling circuit of the present invention.
Fig. 6 is a circuit diagram of an audio amplitude detection circuit in the sidetone canceling circuit of the present invention.
Fig. 7 is a schematic block diagram of a partial circuit in the sidetone canceling circuit of the present invention.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings to which the invention is attached.
The first embodiment is as follows: in the rail transit system, each train is provided with a plurality of talkback terminals, namely a plurality of two-wire full-duplex talkback devices. For example, 5 talkback terminals are provided per train, and when the train is reconnected, 10 talkback terminals are interconnected. When the talkback terminal needs talkback, the talkback bus is accessed, the own voice is transmitted to the bus, and meanwhile, the bus can acquire the bus audio signal to hear the voice of the other party.
In order to be able to hear clear voice of the other party, the two-wire full duplex intercom includes a sidetone canceling circuit. As shown in fig. 1, the side mute circuit includes a switch U1, a power amplifier U5, a series resistor, a transformer T1, and a mute path.
The switch U1 selects an input signal by its connection state, which can be connected to the present voice signal to use the present voice signal as an input signal. In this embodiment, the switch is an alternative analog switch, which has two input ends, where one input end, i.e., the first input end, is connected to the local voice signal, and when the alternative analog switch is connected to the first input end, the local voice signal can be obtained. The alternative analog switch also has another input terminal, namely a second input terminal.
The power amplifier U5 is connected to a switch, here a class AB linear power amplifier, which amplifies the input signal and outputs a differential audio signal. The two series resistors are respectively R1 and R2, and are respectively connected to two output ends of the power amplifier U5. The output of the power amplifier U5 is connected across the primary winding of the transformer T1 through series resistors R1, R2, and the secondary winding of the transformer T1 is connected to the intercom bus. The transformer can transmit an input signal into the bus or obtain a bus audio signal from the bus.
The mute path is connected to the input signal and transformer T1 for signal cancellation of the bus audio signal. The mute path includes a differential input op-amp U3, a digital potentiometer U6, an adder U2, and a controller. The differential input operational amplifier U3, the digital potentiometer and the adder U2 are sequentially arranged.
Two input terminals of the differential input op-amp U3 are connected to the primary winding of the transformer T1, thereby obtaining a bus audio signal, which inverts the bus audio signal to output a single-ended audio signal. The single-ended audio signal is input to one input end of an adder U2 after passing through a digital potentiometer U6, the other input end of the adder U2 is connected with an input signal obtained by a switch through a constant-value resistor R3, so that the adder U2 adds the single-ended audio signal and the input signal to eliminate a part of signals in the single-ended audio signal, and then outputs an opposite voice signal to a receiver. The parameters of the digital potentiometer U6 are adjustable, so that the output signal of the adder U2 can be adjusted by the digital potentiometer U6. The controller is used to control the digital potentiometer U6 to automatically make parameter adjustments.
The controller includes an audio amplitude detection circuit U4 and an MCU. The input end of the audio amplitude detection circuit U4 is connected to the output end of the adder U2, so as to obtain the opposite voice signal output by the adder U2 and perform amplitude detection on the opposite voice signal. The MCU includes two functions, one is that it outputs the adjusting reference signal, the adjusting reference signal is outputted and provided to the switch, namely, one output end of the MCU is connected with the second input end of the alternative analog switch, when the alternative analog switch selects the second input end, the parameter adjusting reference signal provided by the MCU is used as the input signal. The parameter adjusting reference signal is a 1V and 1kHz sinusoidal signal; and secondly, outputting an adjusting signal according to the amplitude of the voice signal of the opposite side to adjust the parameter of the digital potentiometer U6, namely, the input end of the MCU is connected with the output end of the audio amplitude detection circuit U4, and the other output end of the MCU is connected with the digital potentiometer U6.
The circuit diagram of the power amplifier U5 is shown in fig. 2. The circuit diagram of adder U2 is shown in fig. 3. The circuit diagram of the differential input operational amplifier is shown in fig. 4, and includes an operational amplifier, and filter capacitors C264 and C263 are respectively connected in parallel between a non-inverting input terminal and an output terminal of the operational amplifier, and between an inverting input terminal and an output terminal of the operational amplifier. The circuit diagram of the digital potentiometer U6 is shown in fig. 5. The circuit diagram of the audio amplitude detection circuit U4 is shown in FIG. 6, and comprises a true effective value detection chip with a built-in delta sigma algorithm
As shown in fig. 7, in a normal working state, the voice signal of the present invention is divided into two paths after passing through the analog switch U1, wherein one path outputs a differential audio signal through the class AB power amplifier U5, and the differential audio signal passes through the series circuits R1 and R2 and then drives the transformer T1 to be connected to the bus in a butt joint manner; the other path is input to an adder U2 after passing through a constant value resistor R3. After being connected in series, R1 and R2 are subjected to impedance transformation through a transformer T1 to serve as a load of a bus, namely the input impedance of the circuit, and differential voltage signals of the points c and d are reflected on the load by bus audio signals. c. The differential voltage signal of the two points d is converted into a single-ended audio signal inside the device through the differential input operational amplifier U3. The single-ended audio signal is passed through a digital potentiometer and input to the adder U2 together with the present speech signal. The gain of the two signals through the adder U2 is set by a fixed resistor R3 and a digital potentiometer U6, respectively. Because the gain of the differential input op-amp U3 is set to-1, the phase of the local voice signal returned to the summing circuit U2 after passing through the differential input op-amp U3 is opposite to the phase of the source signal, so that the formatted digital potentiometer value cancels the local voice signal from the bus signal, thereby producing a clean opposite voice signal.
The working principle of the whole circuit in the normal working state is further explained below. Taking signal sampling points c and d of a differential input operational amplifier U3 as research objects, Zl as an equivalent load of the whole circuit, Zin as an equivalent input impedance of the whole circuit, and the amplitude of a voltage signal of the local voice (Vs) acting on the Zl is as follows:
the magnitude of the voltage signal applied to Zin by the bus speech (set to Vbus) is:
considering that the output impedance of the power amplifier is small and approximately, the equivalent output impedance at the point c and the point d is Zin, R1 and R2
Therefore, the input signal Vdif of the differential input operational amplifier U3 is:
since the gain of the differential input op-amp U3 is set to-1, the output of the differential input op-amp U3 is-Vdif.
The input of the adder U2 is the local speech Vs with gain 1 and the output-Vdif of the differential input op amp U3.
The output of the adder circuit U2 is therefore (R)PIs a numberParameter value of potentiometer U6):
therefore only need to
Namely:
when the voice is not received, the Vs term in Vo is 0, and the voice of the other party output to the receiver does not include the own voice. Therefore, only Rp needs to be adjusted to the corresponding parameters under different bus impedances.
When a new talkback terminal is connected to the bus or the train is reconnected and the impedance deviation of the connected bus is large so that clear voice of the opposite side can not be obtained, the alternative analog switch is switched to a standard 1V 1KHz sinusoidal signal output by the DAC of the MCU. The output amplitude of the adder U2 is detected by the audio amplitude detection circuit U4 when no signal is input to the counterpart. At this time, the resistance Rp of the digital potentiometer U6 is adjusted by the MCU, and the resistance Rp of the digital potentiometer when the value output by the adder U2 is the minimum is the optimal parameter of the sidetone cancellation circuit. Applying this parameter to the normal operating state of the device will again result in clear speech of the opposite party.
The silencing circuit of the invention makes the talkback voice of the train clear, especially keeps the attenuation of the voice of the train to be more than 20dB under the condition of multi-terminal access and reconnection, thereby realizing the clear talkback function under the condition of the change of the number of bus mounted terminals, or the deviation of mounted equipment from a standard value and the reconnection of the train.
When the talkback device is connected to the talkback bus, the digital potentiometer U6 is adjusted to preset parameters, and the preset parameters are calculated by standard signals of the talkback device and test results of the audio amplitude detection circuit U4. Therefore, the clearness of the talkback voice can be kept under the condition that the number of the access terminals is changed continuously.
In the above side-tone canceling circuit:
1. power amplifier U5
The power amplifier U5 in the circuit adopts AB type linear power amplifier, and because BTL output stage is adopted, the output has no DC component, and no DC blocking capacitor is needed, thus improving the performance of low frequency. The output adopts a differential balance mode, and the EMC performance can be obviously improved.
2. Differential input operational amplifier circuit U3
The circuit consists of an operational amplifier, a resistor and a capacitor, and the common-mode rejection ratio of the input end is improved by butting the talkback audio bus in a balanced input mode. A feedback network of the operational amplifier is connected with capacitors C263 and C264 in parallel to form a first-order low-pass filter, so that signals higher than audio frequency on a bus can be suppressed, and the signal-to-noise ratio of the system is improved.
3. Digital potentiometer U6
The scheme adopts a 7-bit 128-level adjustable digital potentiometer. MCU through I2The C interface is connected to the digital potentiometer chip and writes a required value into a register of the digital potentiometer.
4. Audio amplitude detection circuit
The scheme uses a true effective value detection chip with a built-in delta sigma algorithm as the core of the detection circuit, and the algorithm has more excellent bandwidth and linearity than the traditional detection circuit, and the linearity is less than 0.1%. The follower formed by the operational amplifier is used for outputting the level signal, so that the influence caused by higher input impedance of the MCUADC input end is reduced.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (8)
1. The utility model provides a sidetone eliminating circuit, is applied to two-wire full duplex intercom device which characterized in that: the side-tone eliminating circuit comprises a switch which can be connected with a local voice signal and takes the local voice signal as an input signal, a transformer which is connected with a bus and transmits the input signal into the bus or obtains a bus audio signal from the bus, and a silencing passage which is connected with the input signal and the transformer and eliminates the bus audio signal;
the noise reduction path comprises a differential input operational amplifier which inverts the bus audio signal to output a single-ended audio signal, an adder which adds the single-ended audio signal and the input signal to eliminate partial signals in the single-ended audio signal and output an opposite voice signal, a parameter adjustable digital potentiometer which is arranged between the differential input operational amplifier and the adder and adjusts the output signal of the adder, and a controller which controls the digital potentiometer to automatically adjust parameters;
the controller comprises an audio amplitude detection circuit for acquiring the voice signal of the opposite side output by the adder and carrying out amplitude detection on the voice signal, and an MCU for providing a parameter adjustment reference signal to the switch as the input signal and outputting an adjustment signal according to the amplitude of the voice signal of the opposite side so as to adjust the parameter of the digital potentiometer;
the MCU outputs an adjusting reference signal to the switch as an input signal, the audio amplitude detection circuit detects the output amplitude of the adder when no signal is input to the opposite side, the resistance value of the digital potentiometer is adjusted through the MCU at the moment, and the resistance value of the digital potentiometer when the value output by the adder is the minimum is the optimal parameter of the side-tone cancelling circuit at the moment;
the switch is an alternative analog switch, and has two input ends, namely a first input end for acquiring the voice signal of the local side and a second input end for acquiring the parameter adjustment reference signal.
2. The sidetone canceling circuit of claim 1, wherein: the audio amplitude detection circuit comprises a true effective value detection chip with a built-in delta sigma algorithm.
3. The sidetone canceling circuit of claim 1, wherein: the input signal is input to the adder via a fixed-value resistor.
4. The sidetone canceling circuit of claim 1, wherein: and a power amplifier for amplifying the input signal and outputting a differential audio signal is arranged between the switch and the transformer.
5. The sidetone canceling circuit of claim 4, wherein: and a series resistor is arranged between the power amplifier and the transformer.
6. The sidetone canceling circuit of claim 4, wherein: the power amplifier is an AB type linear power amplifier.
7. The sidetone canceling circuit of claim 1, wherein: the differential input operational amplifier comprises an operational amplifier, and filter capacitors are respectively connected in parallel between the non-inverting input end and the output end of the operational amplifier and between the inverting input end and the output end of the operational amplifier.
8. A two-wire full duplex intercom device is characterized in that: the two-wire full duplex intercom includes the sidetone canceling circuit of any one of claims 1-7.
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| CN201611196681.9A CN106792352B (en) | 2016-12-22 | 2016-12-22 | Side-tone eliminating circuit and two-wire full duplex intercom device using same |
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| CN108566268A (en) * | 2017-12-13 | 2018-09-21 | 苏州长风航空电子有限公司 | Full duplex intercom system applied to rail traffic emulation bus |
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| CN201577120U (en) * | 2009-12-04 | 2010-09-08 | 康佳集团股份有限公司 | Side-tone eliminating circuit of interphone |
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| CN203289520U (en) * | 2013-06-25 | 2013-11-13 | 斯恩威（中国）自控系统工程有限公司 | Talkback sidetone elimination circuit |
| CN105072241A (en) * | 2015-07-31 | 2015-11-18 | 合肥赛为智能有限公司 | Anti-sidetone circuit of intercom system isolation transformer |
| CN105744383A (en) * | 2014-12-09 | 2016-07-06 | 重庆西胜电子科技有限公司 | Duplex interphone capable of eliminating side tone by means of transformer coupling |
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| EP0228455A1 (en) * | 1985-06-27 | 1987-07-15 | Codart Communications, Inc. | Scrambling apparatus |
| WO1999011047A1 (en) * | 1997-08-21 | 1999-03-04 | Northern Telecom Limited | Method and apparatus for listener sidetone control |
| KR100279825B1 (en) * | 1998-12-23 | 2001-02-01 | 윤종용 | Circuit to eliminate echoes and sidetones at the exchange |
| WO2013159359A1 (en) * | 2012-04-28 | 2013-10-31 | Abb Technology Ltd. | An echo cancellation device for a 2-wire intercom system and a method thereof |
| CN105744451A (en) * | 2014-12-09 | 2016-07-06 | 重庆西胜电子科技有限公司 | Duplex interphone capable of eliminating side tone by means of resistance-capacitance network |
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- 2016-12-22 CN CN201611196681.9A patent/CN106792352B/en active Active
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3828146A (en) * | 1973-03-22 | 1974-08-06 | Bell Telephone Labor Inc | Time division conference hybrid circuit |
| CN201577120U (en) * | 2009-12-04 | 2010-09-08 | 康佳集团股份有限公司 | Side-tone eliminating circuit of interphone |
| CN102868942A (en) * | 2012-08-28 | 2013-01-09 | 广东安居宝数码科技股份有限公司 | Voice transmission method and device based on building intercom system, and building intercom system |
| CN203289520U (en) * | 2013-06-25 | 2013-11-13 | 斯恩威（中国）自控系统工程有限公司 | Talkback sidetone elimination circuit |
| CN105744383A (en) * | 2014-12-09 | 2016-07-06 | 重庆西胜电子科技有限公司 | Duplex interphone capable of eliminating side tone by means of transformer coupling |
| CN105072241A (en) * | 2015-07-31 | 2015-11-18 | 合肥赛为智能有限公司 | Anti-sidetone circuit of intercom system isolation transformer |
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Address after: 215153 No. 350 Qingchengshan Road, Science and Technology City, Suzhou High-tech Zone, Jiangsu Province Patentee after: SUZHOU HUAQI INTELLIGENT TECHNOLOGY Co.,Ltd. Address before: 215153 No. 350 Qingchengshan Road, Science and Technology City, Suzhou High-tech Zone, Jiangsu Province Patentee before: SUZHOU HUAQI INTELLIGENT TECHNOLOGY Co.,Ltd. |