A kind of intercom system isolating transformer anti-side-tone circuitTechnical field
The present invention relates to the technical field of the electronic circuit of audio signal, four lines especially for intercom system turn two wires driving isolation transformer anti-side-tone circuit.
Background technology
In vehicle-mounted intercom system, audio frequency intercommunication four line of driving isolation transformer turns two wires scheme and namely simplifies the antijamming capability that car body cabling also enhances audio frequency intercom system, in vehicle-mounted intercom system, have certain realistic meaning.
Share in the intercom system of a channel at analogue audio frequency receiving and transmitting signal, for reducing sidetone to the impact of communication effect, all talk back equipments all need to increase anti-side-tone circuit, anti-side-tone circuit allows audio frequency transmission signal occur by a certain percentage on the transmission line on the one hand, the signal allowing our audio frequency receiving circuit obtain on the other hand is enough little, is unlikely to speaker hears oneself sound from one's own side's loudspeaker.Meanwhile, the anti-side-tone circuit of recipient appears at the input of audio frequency receiving circuit by a certain percentage by the voltage on transmission line, thus recipient's loudspeaker play out sound.Anti-sidetone method has transformer method, bridge balance method and phase-offset method usually.Transformer method is extensive use in dialer formula telephone set once, is eliminated now.Bridge balance method is generally applied in push-button telephone, but has certain limitation, and performance is stable not, send accepted call signal to amplify and just can meet the demands.Phase-offset method is more common in wireless interspeaker and building conversational system.Phase-offset method common at present has multiple circuit form, can find that these circuit good and the bads mix, falsehood often goes out, and all can not solve driving transformer very well in vehicle-mounted analogue audio frequency intercom system realizes phase cancellation anti-sidetone at present.Therefore, prior art needs to improve.
Summary of the invention
The object of the invention is to overcome above-mentioned the deficiencies in the prior art part, provide a kind of intercom system isolating transformer anti-side-tone circuit, solution analogue audio frequency intercom system driving transformer realizes full duplex intercommunication four line and turns two-wire circuit and eliminate the interference of sidetone.
The object of the invention is to be achieved through the following technical solutions: a kind of intercom system isolating transformer anti-side-tone circuit, it is characterized in that: include first order microphone signal amplifying circuit, audio frequency transformer, subtracter, DC bias circuit, second level noise compression amplifying circuit, microphone input signal delivers to audio frequency transformer via first order microphone signal amplifying circuit, the input signal of subtracter to take from first order microphone signal amplifying circuit two different sampled points (V1 and V2), two different sampled point (V1 and V2) signals deliver to end of oppisite phase and the in-phase end of subtracter respectively, after subtracter process, signal sends into second level noise compression amplifying circuit again, decay Processing for removing is done to local sidetone signal.
Further, described first order microphone signal amplifying circuit comprises input stage coupling capacitance (C9, C15) and power amplifier drive circuit, power amplifier drive circuit is made up of power amplifier (U1) and peripheral resistance (R18, R17, R16, R2, R6), electric capacity (C14, C13), its signal single ended input difference output, can control the size of differential signal amplitude by the resistance of regulating resistance (R16); Two equal resistors (R2, R6) rear drive transformers are connected in series at power amplifier (U1) output, then the signal at power taking resistance (R6) two ends inputs to subtracter as the sampled point of the input signal of subtracter, configuration resistance (R6) and resistance (R2) resistance after, can by input signal sampled point (V1 and V2) two signal under the prerequisite being greater than 100Hz phase difference value close to zero.
Described subtracter is made up of the electric capacity (C3, C5, C1, C2) of operational amplifier (N1A) and periphery and resistance (R3, R1, R7, R10, R5, R8, R4); Local microphone signal adjusts in the forward of operational amplifier (N1A) and the signal amplitude of the reverse input end resistance by regulating resistance (R7), resistance (R10), and makes amplitude equal; Regulating resistance (R1) and the ratio of resistance (R3), can control output signal (Vout) amplitude size.
Described second level noise compression amplifying circuit is made up of chip (U2), resistance (R9, R13, R14, R15), electric capacity (C4, C10, C11, C12); The resistance of regulating resistance (R13, R15) can regulate noise reduction threshold values and compression multiplication factor; The signal at sampling resistor (R6) two ends inputs to subtracter, makes, when audio-frequency bus signal inputs this amplifying circuit, to put the audio-frequency bus signal that potential difference equals 1/2nd between different sampled point (V2 and V1); When sampling local signal, sampled point (V2) signal is decayed through resistance (R7) and resistance (R10) dividing potential drop again, and the signal amplitude that sample bus is come is greater than the local signal amplitude of sampling.
Audio frequency transformer is made up of transformer (T1), TVS pipe (D5), magnetic bead (L6, L7), filter capacitor (C40).
Described DC bias circuit is made up of the electric capacity (C6, C7) of operational amplifier (N1B) and periphery and resistance (R11, R12), by resistance (R11, R12) dividing potential drop fortune make calculation amplifier (N1B) in the same way terminal voltage be 1/2nd times of operational amplifier (N1B) supply power voltage, fortune is made reverse input end and the output short circuit of calculation amplifier (N1B), realize voltage follow, for subtracter provides reference voltage.
Technical scheme of the present invention, has advantage as follows:
1. present invention achieves in industry and drive full duplex intercommunication four line of a transformer to turn two-wire circuit, optimize the cabling of intercom system, multiple equipment can be directly connected by one group of bus.
2. the invention solves and to utilize when driving transformer in phase-offset method anti-sidetone method because of sidetone interference problem that phase difference brings.
3. the present invention utilizes the isolation characteristic of transformer to achieve multiple equipment cascading and mutual independence.The trouble of uniting and adjustment is needed when interference when solving multiple equipment cascading between each equipment and cascade.
4. in the present invention, transformer adopts power amplifier differential driving, thus it has stronger driving force and carrying load ability, solves common because of long range propagation with cross the problem of pressure drop brought.
5. relatively other full duplex intercommunication four lines turn two-wire circuit the present invention and have the features such as electric structure is succinct exquisite, with low cost, easy realization.
Accompanying drawing explanation
Fig. 1 is circuit block diagram of the present invention.
Fig. 2 is circuit theory diagrams of the present invention.
Fig. 3 is the circuit diagram of the first order microphone signal amplifying circuit in Fig. 1.
Fig. 4 is the circuit diagram of the audio frequency transformer in Fig. 1.
Fig. 5 is the circuit diagram of the DC bias circuit in Fig. 1.
Fig. 6 is the circuit diagram of the subtracter in Fig. 1.
Fig. 7 is the circuit diagram of the second level noise compression amplifying circuit in Fig. 1.
Embodiment
For making object of the present invention, technical scheme and advantage clearly, clearly, referring to the accompanying drawing embodiment that develops simultaneously, the present invention is described in further detail.
See Fig. 1 and Fig. 2, the anti-side-tone circuit of the present embodiment includes first order microphone signal amplifying circuit, audio frequency transformer, subtracter, DC bias circuit, second level noise compression amplifying circuit.
See Fig. 2 and Fig. 3, described first order microphone signal amplifying circuit comprises input stage coupling capacitance C9, C15 and power amplifier drive circuit, and power amplifier drive circuit is by power amplifier U1 and peripheral resistance R18, R17, R16, R2, R6, and electric capacity C14, C13 form.This amplifying circuit realizes signal single ended input difference output, can be controlled the size of differential signal amplitude by the resistance of regulating resistance R16.Add coupling capacitance C9, C15 main purpose is logical friendship every straight effect, it is higher that the quiescent point of introducing to operational amplifier cascade of DC component arranges requirement, and the stability of circuit can be reduced, the operational amplifier of each several part can be arranged quiescent point separately after adding coupling capacitance, not have interference each other.The load capacity of audio-frequency bus can be strengthened with power amplifier driving transformer, power amplifier is difference output, audio-frequency bus signal amplitude is then the single ended voltage 2 times of power amplifier U1 output, introduces the anti-sidetone signal of subtracter like this and is decayed, and is conducive to the amplitude reducing sidetone.
See Fig. 2 and Fig. 4, audio frequency transformer is by transformer T1, TVS pipe D5, magnetic bead L6, L7, and filter capacitor C40 forms.Do external interface with audio frequency transformer, achieve the mutually isolated of each equipment room, improve the stability of system.Use the isolation advantages of transformer, when transformer primary side system malfunctions is as short circuit, overvoltage etc., transformer time edge system can not be damaged and disturb.TVS pipe D5 effectively can suppress the high pressure of bus, by high-frequency signal on magnetic bead L6, L7 and filter capacitor C40 filtering bus, suppresses the interference of extraneous high-frequency signal.
See Fig. 2 and Fig. 6, the subtracter used is by the electric capacity C3 of operational amplifier N1A and periphery, C5, C1, C2 and resistance R3, R1, R7, R10, R5, R8, R4 forms, adopt the phase-offset method that associative operation amplifier is built, by the resistance of regulating resistance R7 and R10, make local microphone signal equal with reverse input end signal amplitude at the forward of operational amplifier NIA, as output signal Vout=(V2 × R10/ (R7+R10)-the V1) × R1/R3 of subtracter in Fig. 6, the ratio of regulating resistance R1 and R3, the amplitude size outputing signal Vout can be controlled.Key features is sampled point V1, V2 of subtracter input signal, from Fig. 2 and Fig. 6, two equal resistors R2, R6 rear drive transformers are connected in series at power amplifier U1 output, then the signal at power taking resistance R6 two ends inputs to subtracter, after the resistance of reasonable disposition resistance R6 and R2, input signal sampled point V1 and V2 two signal phase difference value under the prerequisite being greater than 100Hz, close to zero, can be realized phase-offset method anti-sidetone, the phase difference value of sampled point V1 and V2 is one of essential condition.
See Fig. 2 and Fig. 7, described second level noise compression amplifying circuit is made up of chip U2, resistance R9, R13, R14, R15 and electric capacity C4, C10, C11, C12.Utilize the feature of its automatic noise reduction compression, regulating resistance R13, R15 can regulate noise reduction threshold values and compression multiplication factor, and the multiple proportional that this amplifying circuit can be less than the target signal filter of noise reduction threshold values and be greater than the signal pressing convergent-divergent of noise reduction threshold values large exports.This amplifying circuit is while the multiple equipment of bus carry, the amplitude of input signal sampled point V1 and V2 is one of essential condition, the signal at sampling resistor R6 two ends inputs to subtracter, can make, when audio-frequency bus signal inputs this amplifying circuit, between input signal sampled point V2 and V1, to put the audio-frequency bus signal that potential difference equals 1/2; When sampling local signal, sampled point V2 signal is decayed through resistance R7, R10 dividing potential drop again, this ensure that the signal amplitude that sample bus is come is greater than the local signal amplitude of sampling, eliminate small-signal for rear class and provide superior condition, the signal that bus can be made to come is in the transmission of second level noise compression amplifying circuit, and local signal is eliminated in the decay of second level noise compression amplifying circuit.Even if cause the change of the difference in magnitude of input signal sampled point V1 and V2 because of carry quantity, as long as reasonable disposition resistance R7 and resistance R10, all can realize local signal (i.e. sidetone) and eliminate in the decay of second level noise compression amplifying circuit.
See Fig. 2 and Fig. 5, DC bias circuit is made up of electric capacity C6, C7 of operational amplifier N1B and periphery and resistance R11, R12.By the voltage follower that operational amplifier is set up, for subtracter provides reference voltage, by resistance R11, R12 dividing potential drop make operational amplifier N1B in the same way terminal voltage be 1/2 times of operational amplifier N1B supply power voltage, by the reverse input end of operational amplifier N1B and output short circuit, realize voltage follower.Because its voltage follow has very high input impedance and very low output impedance, high input impedance can alleviate the impact on signal source, almost draw electric current from signal source, there is extremely low output impedance simultaneously, voltage drop is caused in inside hardly to during negative sanction output current, can be considered voltage source, thus improve antijamming capability.
In the present embodiment, the concrete model of operational amplifier is LM6482, and the concrete model of chip U2 is SSM2167, and the concrete model of power amplifier U1 is LM4781.
Should be understood that; the application of this patent is not limited to above-mentioned citing, for those of ordinary skills, can be improved according to the above description or convert; all these improve and convert the protection range that all should belong to this patent claims, repeat no more here.