CN1060376A - The coupling circuit that is used for two wire transmission systems - Google Patents

Abstract

A kind of two pairs 4 line hybrid coupled circuit.Described circuit has two extra " sidepiece " coils and is connected to existing output transformer, and the coil that is increased has improved the signal strength signal intensity of received signal, and has eliminated the feedback from output amplifier effectively.

Description

The coupling circuit that is used for two wire transmission systems

The invention belongs to the digital data transfer field, especially, the present invention relates to noise filtering, the amplifying circuit of two wires data transmission circuit.

It is known using couple of conductor to come transmitting digital information.Can be with this two-wire system many different devices that interconnect, these devices comprise computer and telephone-switching network, in two-wire system, data receive on these two identical lines simultaneously and send.When a two wire transmission systems is connected to computer or similar device, need the coupling circuit that digital information can be sent into computer and therefrom send out, sort circuit is called as two pairs four line transducers or hybrid coupled circuit, and its general example is illustrated among Fig. 1.In Fig. 1, system 10 is made up of a two wires transmission medium, first digital device 12 and second digital device 14.Each digital device contains reception and transmit amplifier, and transmission and reception amplifier are connected to transmission medium 11, and reception amplifier 13 and transmit amplifier 15 are in equipment 12, and transmit amplifier 19 and reception amplifier 17 are in equipment 14.In this is used, the circuit that sends and reception amplifier is coupled to this two-wire system is called as mixing is coupled circuit.Be coupled the synchronous transmission on the circuit and receive normally in this mixing and realize that wherein, reception amplifier and transmit amplifier all are connected to a pair of lead by the 2 pairs 4 line conversions.A kind ofly be used on a two wires transmission medium transmission and receive simulation and the two system of digital signal has been disclosed in U.S. patent application case the 07/385th, in No. 610, " the additional main line system of numeral " (DigitalAdded Main Line System) by name quotes this application case usefulness for your guidance herein.

Above-mentioned set-up mode has some intrinsic problems.The signal that is transmitted is quite strong basically, has an amplitude that reaches three ten-day period of hot season spy.After transmission-line attenuation, received signal is normally one very little, is typically about several millivolts.When the part of institute's transmission signals fed back to reception amplifier, the transmission signal of high amplitude will be eliminated the signal of coming in.In addition, though the impedance of transmission line and transmitter must be mated, so that on this a pair of two-wire, obtain maximum power delivery, but add the signal of wherein also further having decayed and having entered with the impedance that improves transmission characteristic, at last, the noise that enters must filtering from the signal that enters, and receive to improve, but described filtering must not have influence on the signal of outside output.

The problems referred to above are well-known in the art, and the trial of existing every solution.A kind of known mixing is coupled circuit table and is shown among Fig. 2, with output transformer T ₁And with in, resistance R F ₁Be feed-in resistance, its value is elected impedance and the load ZL impedance matching that makes transmitter as, can obtain maximum transmission power.Supposing the system becomes mirror image mapping at the line position that is designated as " Sym ", and ZL is 135 ohm, if T ₁No resistance, then two RF ₁To be 67.5 ohm.Vprime will be this RF of 1/2Vout( ₁Effect as same bleeder circuit), and each end of circuit can promote the other end to obtain maximal efficiency.Resistance R F ₂Map out present transformer T with impedance Z R in order to mirror image ₁Voltage on the primary coil, the voltmeter of this mapping is shown VRef.In a preferred embodiment, this RF ₂With ZR and RF ₁Multiple (be RF here ₁5 to 15 times), and RD ₁And RD ₂Equate and be approximately RF ₂5 to 15 times, it is zero that a signal that sends from Vout causes VRec, this is because RD ₁And RD ₂Voltage divider cause.Dividing potential drop between VRef and the Vprime causes the paraphase output signal, and original output signal synchronously is added to reception amplifier.This two signal disappears each other mutually, causes the very big minimizing of the output signal that feeds back to receiver.At the same time, the signal Vsecond that enters changes, and Vout still remains zero.As long as Vout still is zero, then VRef still is approximately zero, and VRec equals 1/2Vprime, and this is by by RD ₁And RD ₂The voltage divider that is constituted receives.

About output characteristic, the output of circuit equals among Fig. 2:

VRec=VprimeRD ₂(RD ₁+ RD ₂)=Vprime/2 works as RD ₁=RD ₂The time.

Though the circuit among Fig. 2 has lowered the feedback signal that enters receiver widely, because voltage divider, its signal of entering of still having decayed is about 1/2, therefore, is necessary to keep the signal cancellation characteristic of circuit among Fig. 2, but still the entering signal that can be improved.

The present invention is the improvement that known mixing is coupled circuit, by adding extra side coil to coupling transformer, and RF ₁Be connected to the central coil of improved transformer and each RD ₁Be connected to the external coil of this improved transformer, strengthen in the received signal intensity ratio prior art.In this way, VRec/Vprime maximum convergence 1 is different from the maximum 1/2 in the prior art.

Because increase the impedance of ZR, received signal strength signal intensity also can increase, and causes VRef greater than Vprime.In some cases, ZR comprises a transformer.When using transformer, on the secondary coil of transformer, measure VRef.Wherein, VRef can be at random greater than Vprime.

The following accompanying drawing of reference to doing further to describe in the detailed description of embodiment to the present invention.

Fig. 1 represents general 2 couple 4 line transmission systems;

Fig. 2 represents that a kind of known 2 couple, 4 lines mix the schematic diagram that is coupled circuit;

Fig. 3 is a schematic diagram of the present invention; And

Fig. 4 is the schematic diagram of another embodiment of the present invention.

Fig. 3 represents preferred embodiment of the present invention.When with Fig. 2 circuit relatively the time, two extra " sidepieces " or coil have been added in transformer T ₁Primary side on, and RD ₁And RF ₁Connection reset slightly: RF ₁Still be connected to central authorities " original " winding, and RD ₁Be connected to T now ₁Go up new, extra overhang.

This extra coil and the resistance of resetting can increase the ratio of VRec/Vprime, and from about 0.5 to almost 1, thereby the signal strength signal intensity of measured entering signal is increased be twice.Certainly, according to VFeedback to the ratio (being called X herein) of Vprime and VRef to the ratio (being called Y herein) of Vprime and decide, may obtain various result.

As in the prior art, RF ₁Still be configured to be matched with load impedance ZL, so that suitable internal driving is provided.Because RF ₁Value be 1/2 of ZL, therefore come balance sysmte with two this resistors.RF ₂Be chosen with ZR and make 2RF ₂+ ZR sum is between 2RF ₁Between 5 to 10 times of+ZL sum.ZR is set so that VRef is bigger 1.2 to 1.5 times than Vprime.Because Y is the ratio between VRef and the Vprime, so RD ₂=YN and RD ₁=XN, wherein N is any suitable numerical value, to prevent the system of loading on and to provide rational impedance to receiver system.If only have this side coil to be added to transformer, RD then ₁Value must increase, with the Transformer Winding that is increased than proportional, so that keep VRec to equal zero.If only consider the increase of VRef with respect to VPrime, then RD ₂Must increase by a coefficient Y, equal zero to keep VRec.

In circuit shown in Figure 3, VFeedback=XVprime, wherein X is the ratio between VFeedback and the Vprime.As defined above, Y equals VRef/Vprime.At first

VRec＝VFeedback·RD ₂/（RD ₁+RD ₂）

Yet, because RD in this embodiment ₁In fact equal XRD ₁And RD ₂Equal YRD ₂

VRec=XVprimeYRD ₂/ (XRD ₁+ YRD ₂) and RD ₁=RD ₂, after the simplification

VRec＝Vprime.X·Y/（X+Y）

Now consider the work of circuit among Fig. 2, wherein VRec=(Vprime/2), the results of property of system equals after revising:

VRec＝（Vprime/2）2X·Y/（X+Y）。

As shown in Figure 3, be used for preventing that the original voltage offset of output signal feedback is still identical with prior art, the paraphase of output signal and normal output signal always are added to input amplifier simultaneously, thereby have eliminated effectively by sending the backspace feedback that signal caused.

In a specific embodiment, VFeedback/Vprime equals 3, and VRef/Vprime equals 1.5.Received signal strength signal intensity increases 6db in signal intensity ratio Fig. 2 circuit of received signal.

In preferred embodiment, Z _RFirst resistance that comprises one 532 Ω is connected in series to the parallel connection combination of one 0.015 μ f electric capacity and a 3k Ω resistance.RF ₂Equal 210 Ω, RD ₂Equal 13k Ω, RD ₁Deng 30k Ω, and RF ₁Equal 38.7 Ω.Transformer T ₁Have one 3 to 1.32 ratio of winding, and with one 0.0047 μ f electric capacity bridgings on Vprime.Other specific component values also can be chosen so that optimized performance.

As previously mentioned, the performance of device will be improved or change to many may the variation of resistance and resistance value.In Fig. 3 embodiment, the Y maximum is 2, and having limited VRec is 2 to the ratio of Vprime.Among Fig. 4, wherein impedance Z R is replaced by a transformer with additional impedance, and Y can be big arbitrarily, causes VRec big arbitrarily to the ratio of Vprime.

Although possible variation has been provided these scopes, it must be appreciated that illustrated embodiment only supplies the usefulness of explanation, and is not to be used for change, restriction or the limitation scope of the invention.Many other modifications and variations may be implemented in the circuit that discloses here, and without departing from the spirit and scope of the present invention.

Claims (4)

1, a kind of 2 couple, 4 line coupling circuits that are used to have 2 line transmission mediums of load impedance comprise

Be used to amplify the output amplifying device of output signal,

The output impedance device is connected to this output amplifying device, makes the load impedance of the impedance matching of this coupling circuit in this transmission medium,

Input amplification device is connected to transmission medium, is used for amplification input signal,

The input impedance device is connected to this input amplification device and this output amplifying device, is used to offset the output feedback from this output amplifying device, and there is a reference voltage in these input impedance device two ends, and

Device for transformer, be connected to this output impedance device, this input impedance device and this transmission medium, be used to connect described 2 pairs 4 line coupling circuits to described transmission medium, this transformer includes a center tap coil, it has an elementary load voltage across thereon, and several side coil, be connected to this center tap overhang, this side coil and this center tap coil have a feedback voltage and are across in this combination, the ratio of described feedback voltage and described primary voltage forms a ratio X, the ratio of described reference voltage and described elementary load voltage forms a ratio Y, wherein equals described elementary load voltage across the measured voltage of this input amplification device and is multiplied by an X and takes advantage of Y to remove the coefficient that X adds Y again.

2,2 pairs 4 line coupling circuits according to claim 1 is characterized in that the estimated rate of X equals 3 to 1.

3, a kind of coupling circuit that is used for the two wires transmission medium, described coupling circuit includes a coupling circuit impedance and a center tap transformer, across the voltage of whole transformer the ratio across the voltage of this center tap coil is defined as X, and the voltage that is across described coupling circuit impedance is defined as Y to the ratio across the voltage of this center tap coil, and described circuit has a 2XY/(X+Y) transfer characteristic.

4, coupling circuit as claimed in claim 3 is characterized in that, Y equals 2, and X equals 3.

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