CN1114488A - Corrector for video transmission on wire and cable - Google Patents

Abstract

The transmission corrector for correcting amplitude fading and frequency distortion of video signals after long-distance transmission over cable or line and suppressing common-mode interference mainly features that a compensating network is combined with current difference input amplifier for continuous compensation step by step. It cooperates with final output stage with variable gain and high-frequency compensation for correction.

Description

Corrector for video transmission on wire and cable

1, technical field

The invention relates to the video correction device, particularly about video by electric wire (single-core shielding line, twin cable, twin-core twisted wire, ordinary telephone line) or the caused amplitude fading of cable transmission, the correction of frequency distortion and common mode disturbances.

2, continuous development along with TV applications, the long Distance Transmission problem of TV signal more and more comes into one's own, yet transmission technology in the past, or require with expensive advanced video cable, or circuit requirement has many group supply power voltages, or require to suppress big common mode disturbances with transformer coupled, though the ability that the inhibition common mode disturbances is also arranged that has, dislike too narrow but scope is total, have for transmission such as telephone wires, need the handlebar unbalanced signal to transfer the transmitter of balanced signal to, with the receiver that balanced signal is transferred to unbalanced signal again and carry out the cable compensation, the overlength cable also needs to add in the centre intermediate amplifier of relaying relay, and this has increased the kind and the complexity of circuit undoubtedly, thereby has increased price.Then not having of having not only is applicable to cable but also be applicable to the compatibility that the electric wire transmission is proofreaied and correct.

The present invention proposes a kind of single power supply, transmission can both be proofreaied and correct and be need not uneven transmitter to the balance conversion to cable or wire, and the present invention both can make the end correction device, also can make relaying relay adjuster, and the ability of the Chinese People's Anti-Japanese Military and Political College in the common mode disturbances of supply power voltage arranged.

3, the objective of the invention is to solve long Distance Transmission vision signal under nonequilibrium condition, and simplify transmission equipment and reduce transmission cost, improve the stability and the reliability of equipment with cable or ordinary telephone line.

4, technical scheme

Be familiar with this professional people for those, after the explanation below reading in conjunction with the accompanying drawings, will have clear and definite understanding various advantages of the present invention.

Fig. 1 is the overall circuit block diagram of drawing according to technology of the present invention:

(A-E) is that the alternation that transmission line and benefit thereof are tasted grid is simplified and the process of derivation schematic diagram to Fig. 2;

Fig. 3 is the circuit diagram of coupling isolation level;

Fig. 4 is the compensation amplification grade circuit that actual compensating network combines with the difference between current input amplifier;

Fig. 5 is the amplifying stage that contains the variable gain of direct current recovery;

Fig. 6 is a high frequency compensation;

Fig. 7 is an adjustable gain final stage output stage.

We will get back to Fig. 1 to Fig. 7 now. At first we tie technical scheme of the present invention Close the block diagram of Fig. 1 and do an introduction of summarizing, successively each several part is done detailed saying then Bright.

The uneven vision signal that needs to proofread and correct arrives figure through electric wire or the long Distance Transmission of cable The input of the coupling isolation level 1 of 1 block diagram, the coupling isolation level plays and transmission line or electricity The characteristic impedance of cable is complementary, and the compensating network in the isolation subsequent compensation amplifier is to passing The impact of defeated line impedence coupling. Cause after 2 pairs of transmission of compensated amplifier line length Distance Transmission Amplitude fading and frequency distortion compensation after deliver to the input of variable gain amplifying stage 3, The variable gain amplifying stage compensates again to the amplitude fading of different length transmission line. By The signal that the gain amplifying stage that can decline is exported is delivered to the input of high frequency compensation gain stage 4, This frequency distortion to the transmission line HFS remakes further correction, and delivering to afterwards can Transfer gain final stage output stage 5, proofread and correct the amplitude fading that the high frequency compensation level is introduced at this, and As the load of output drive level driving receiving terminal, they can be such as monitor, record Camera, the equipment such as video switch also can be the present invention self who uses as middle relay.

We get back to Fig. 2 (A-E) now. As everyone knows, desirable for such as Fig. 2 A Uniform transmission line is when the terminate load resistance R of internal resistance Ri and the transmission line of signal source_LWhen all equaling the characteristic impedance Ro of transmission line itself, i.e. Ri=R_LDuring=Ro, signal will transmit along the transmission line areflexia losslessly, and is the terminate load resistance R_L=Ro all absorbs, and this just It is so-called complete match condition.

In fact, any accurate electric wire or cable of making all can not be desirable, it Distributed resistance is arranged, can produce from direct current until the amplitude loss of high frequency has distributed inductance Reaching distribution capacity and these distribution parameters in fact can not do in full accordly. They Also can change with the variation of environmental condition and frequency, therefore can not accomplish from low frequency extremely The fully coupling of the whole frequency range of high frequency, these all indicating signal by long apart from electric wire or The distortion of the aspects such as meeting introducing amplitude, frequency and phase place after the cable transmission. Particularly from warp The Ji angle is set out, and adopts second-rate cable even pass with transmission lines such as ordinary telephone lines When defeated, can introduce bigger distortion, meanwhile also can be attended by the common mode disturbances of low frequency, These all can damage the image quality of television transmission widely.

The actual transmissions line is a distributed constant, for the purpose of easy analysis, the equivalent transmission line circuit that has signal source internal resistance Ri and terminate load resistance R 1 shown in Fig. 2 B, r among the figure _o' r _b', r _o", r _b", La ＇, Lb ＇, La ", Lb " represent the lump equivalent resistance and the inductance of electric wire or cable go-and-return line or heart yearn and crust, r respectively _o, Co represents between line respectively or leak resistance and concentrated distributed capacitance in the equal set between heart yearn and crust.According to network analysis, the circuit of Fig. 2 B can be simplified to the circuit of Fig. 2 C, wherein r fully _o=r _o'+r _o", r _b=r _b'+r _b", La=La ＇+La ", Lb=Lb ＇+Lb ".

Ohmic leakage r _oGenerally very big, little to the transmission characteristic influence, we think that it is equivalent to open circuit (r for simplicity _o→ ∞).In addition as can be known, when the transmission line mismatch, if the characteristic impedance Ro＞R of transmission line from theory analysis _L, transmission line can replace with a concentrated residual induction, and as Ro＜R _LThe time, transmission line then available concentrates the residue shunt capacitance to replace, and in order further to simplify the analysis of circuit, we can regulate R _LBe slightly larger than Ro.Make whole transmission line system satisfy available one and concentrate the slight mismatch Conditions of residue shunt capacitance equivalence, such equivalent electric circuit is shown in Fig. 2 D.So just make us might simplify analysis widely, and draw useful results.

We introduce the input impedance R of compensating network RcCc and following stages on the basis of Fig. 2 D now _D, the circuit that obtains like this such as Fig. 2 E.

To the analysis showed that of Fig. 2 E, be the voltage signal source Vin of Ri when being added to the input of transmission line when having internal resistance, arrive terminating resistance R through transmission line equivalent network transmission back _L, and through compensating network RcCc with it the series connection R _DThe electric current of last generation is determined by following formula: $I_{\mathrm{RD}}=\frac{\mathrm{Vin}{R}_L}{(R_L+R_D)(\mathrm{Ri}+R_L+r_o+r_b)-{\mathrm{<figure-callout\; id="2"\; label="R\; L"\; filenames="A9410802900111.png"\; state="\{\{state\}\}">R</figure-callout>}}_L^{}+\mathrm{j\&omega;Co}(\mathrm{Ri}+r_o)[(\mathrm{Ri}+R_D)(R_b+R_L)}$ $-R_L^2]+\frac{\mathrm{Rc}(\mathrm{Ri}+R_L+r_o+r_b)[1+j\mathrm{\&omega;Co}(r_b+R_L)(r_o+\mathrm{Ri})/(\mathrm{Ri}+R_L+r_o+r_b)]}{1+\mathrm{j\&omega;RcCc}}$ From top expression formula as can be seen, when

(Ri+R _D) (r _b+ R _L)-R _L ²=o and RcCc=(r _b+ R _L) (r _o+ Ri) Co/ (Ri+R _L+ r _o+ r _b) time, electric current I _RDTo become the function with frequency-independent, the voltage that it produces on RD also will be the function with frequency-independent.But such connection is bad directly to be put to practicality.The at first access of RcCc, it and R _DThe big high attenuation of dividing potential drop meeting is at R _DThereby the signal voltage of last generation reduces signal to noise ratio; Secondly, the last generation of RD be uneven vision signal, also may have very big low frequency common mode disturbances on it, be difficult to obtain good inhibition with general method; The having access to the terminal matching condition that to destroy electric wire or cable of the 3rd RcCc network and cause the reflection effect of transmission line.

For this reason, we are the input impedance R of compensating network RcCc among Fig. 2 E and following stages _DAnd keep apart with the emitter-base bandgap grading loader of forming by C1, R2, Q1, R3 shown in Figure 3 between the transmission line.301,302 inputs of the terminal map interlinking 3 of Fig. 2 E transmission line, the RL with among (R1+RV1) adjustable resistance replacement Fig. 2 E regulates (R1+RV1) and makes it just equal the characteristic impedance of transmission line.(transmission line may be various two-wire lines, single-core shielding line or cable, their characteristic impedance is different) make transmission line reach matching status as far as possible, do not produce reflection.

The level output 303 of penetrating of Q1 connects the input 303 that compensates amplifying stage Fig. 4 among Fig. 3, and C2, C3 can be considered short circuit to interchange among Fig. 4.The RC network of forming by RV2, RV3, RV4, R4, R5, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13 etc. be equivalent to Fig. 2 E center the RcCc compensating network they with the variation of cable or electric wire length, earlier do step-type roughly selecting by S11-4 and S21-4, make electric wire or cable all can access satisfied compensation by RV2, RV3, RV4, adjustment that work is thin again to different length, because it is separate that the isolation of emitter follower makes the adjusting of the coupling of electric wire or cable and compensating network among Fig. 3, is independent of each other.

The common junction of the output of compensating network, RV4, C12, C13 is received the bearing into end of amplifier U1, also is connected to the end of amplifier negative feedback resistor R7 at this point.Because degree of depth negative feedback, the negative input end of U1 can be considered the virtual earth point, as seen from Figure 4, the RD resistance that is equivalent among Fig. 2 E in the compensation grid has not existed, therefore the signal voltage of this point is zero, but signal code is non-vanishing, and it has so just changed voltage input signal the amplification of electric current input into simply by the adjusting decision of the amplitude and the compensating network of input signal.Improved the problem of the signal to noise ratio deficiency that produces because of voltage signal is too little.

U1 seems to be general operational amplifier among Fig. 4, and it is a difference between current (NORTON) input amplifier in fact.General amplifier does not possess strong common mode inhibition capacity, and logical (NORTON) amplifier of sieve then has the ability that suppresses to be higher than the power supply common mode disturbances, thereby than the circuit of the anti-common mode disturbances of general difference type better common mode rejection performance is arranged.The low-frequency gain of amplifier U1 is by ratio among Fig. 4 $\frac{-R7}{\mathrm{<figure-callout\; id="2"\; label="RV"\; filenames="A9410802900111.png"\; state="\{\{state\}\}">RV</figure-callout>}2+R4+\mathrm{<figure-callout\; id="3"\; label="RV"\; filenames="A9410802900111.png"\; state="\{\{state\}\}">RV</figure-callout>}3+R5+\mathrm{RV}4}$ Decision, and the adjusting of RV2+RV3+RV4+R4+R5 is subjected to frequency compensated restriction, so the adjusting of its low-frequency gain is not random.The output 403 of U1 connects the input 403 of variable gain amplifying stage Fig. 5 for this reason.Fig. 5 comprises the DC restoration circuit of being made up of C14, R8, D1, R9, R10, R11 and C15, it returns to the sync item by the vision signal of U1 output among Fig. 4 by R9, R10, R11 voltage divider on the direct voltage that produces on the capacitor C 15 by C14, R8, D1, reduce the dynamic range of signal on amplifier U2, in the hope of obtaining better linearity.

Emitter follower Q2, R12 play cushioning effect, to improve the effect that direct current recovers.

Amplifier U2 is exclusively used in the independent regulation of signal gain, with in the compensating wire cable transmission and the decay introduced in the prime compensating circuit.

The input 501 of high frequency compensation level Fig. 6 is delivered in the output 501 of U2 among Fig. 5.Here high frequency distortion is compensated once more.

The original high frequency compensation of in Fig. 5, also can introducing in the feedback control loop of U2 amplifier, but on some frequency, cause destabilizing factor such as parasitic oscillation probably because of the phase shift in the loop feedback, and also its compensable scope can not be too big.

Circuit shown in Figure 6 comprises the emitter-base bandgap grading output buffer of being made up of R14, Q3, R15, and it keeps apart the U2 among compensating network and Fig. 5.By the attenuator that RV6, R25 form, reach by R16 one R23, the peaking network that C16-C23 forms, and RV6, R25 realizes further high frequency compensation together jointly, to remedy the deficiency that Fig. 4 compensates amplifying stage.Because compensating network not in feedback control loop, is difficult for causing parasitic oscillation, and bigger compensation range is arranged.

The network of being made up of R16-R23 and C16-C23 can compensate high frequency in sizable scope with the centre tapped adjusting of RV6, and it can also make modular, by different compensation range changing-overs.

The emitter follower of being made up of R24, Q4, R26 plays the cushioning effect between last utmost point output stage Fig. 7 of peaking network and adjustable gain.

The output 601 of Fig. 6 Q4 connects the input 601 of adjustable gain end utmost point output stage Fig. 7, U3 also is a variable gain amplifier, it compensates the decay of being introduced by RV6, R25 among high frequency compensation level Fig. 6, and power output is with excitation graphics monitor, video tape recorder, video switch ... or the like equipment.

RV7 and R27 among Fig. 7 are determining Amplifier Gain.R28, R29, R30, R31 are 75 Ω output resistances of amplifier.This output stage has 2-4 tunnel outputs, and the function of video distributor is arranged.

5, the present invention has compared with background technology

A, only use single supply

B, circuit are simple

C, need not uneven conversion to balance

D, need not many kinds such as transmitter, pilot servomotor and receiver, only can realize centre relay and reception, the necessity of having exempted transmitter with same kind.

The compensation way of e, two kinds of uniquenesses all not in feedback loop, is not prone to the parasitic oscillation problem

F, there is multichannel to distribute output function

G, the ability of very strong anti-common mode disturbances is arranged

H, the present invention can be applicable to the correction when vision signal is transmitted simultaneously in transmission lines such as telephone wire, cable, single-core shielding line, twisted-pair feeder, two parallel lines.

I, wide compensation range is arranged

Claims (9)

1, a kind of corrector for video transmission on wire and cable is used for to proofreading and correct by caused amplitude fading, frequency distortion and common mode disturbances behind ordinary telephone line single-core shielding line, twisted-pair feeder, two parallel lines, the isometric Distance Transmission signal of vision cable line.It compensates amplifying stage (Fig. 4) by coupling isolation level (Fig. 3), variable gain amplifying stage (Fig. 5), and high frequency compensation level (Fig. 6) and adjustable gain final stage output stage (Fig. 7) are formed.

Deliver to coupling isolation level (Fig. 3) input through the vision signal that electric wire, the long Distance Transmission of cable are come, through the coupling isolation level compensating network in the coupling terminating resistance of transmission-wire terminal and the subsequent compensation amplifying stage (Fig. 4) is kept apart, avoid influencing each other between them.

The compensation amplifying stage is according to the network of the present invention's derivation and with the amplitude fading of difference between current (NORTON) input amplifier that links to each other to introducing because of electric wire, cable transmission, and frequency distortion and common mode disturbances etc. is proofreaied and correct.

The signal of having proofreaied and correct is delivered to variable gain amplifying stage (Fig. 5) and is carried out the amplitude correction first time.

The output of variable gain amplifier is delivered to high frequency compensation level (Fig. 6) high fdrequency component of transmission signals is remake further compensation.

Signal after high frequency compensation is delivered to adjustable gain final stage output stage (Fig. 7) to proofread and correct total amplitude fading that the high frequency compensation level is introduced.

2, said coupling isolation level is meant by the emitter-follower among Fig. 3 and as isolation level the terminating resistance of the frequency compensation network that derives among Fig. 2 E and transmission line and terminal thereof is left in the claim 1, and their adjusting is not influenced each other.

3, said terminal terminating resistance comprises the resistance combination that a little fixed resistance and variable resistor are in series in the claim 2, is transferred near the characteristic impedance of this transmission line with them at different transmission lines, in the hope of obtaining and best matching state.

4, said compensating network is can both compensate the compensating network that derives from Fig. 2 E by the transmission line to dissimilar different lengths and the stepping of being selected by toggle switch that proposes and continuously adjustable three joints or more piece RC network are formed in claim 1 and the claim 2.

5, the said compensation amplifying stage of claim 1 is made of jointly said compensating network in claim 2 and 4 and a difference between current (NORTON) input amplifier.They become the signal transition of voltage input the form of electric current input to improve signal to noise ratio.The difference between current input amplifier combines with compensating network, has improved the ability of the anti-common mode disturbances of circuit widely, and its amplification has also compensated amplitude fading simultaneously.

6, said variable gain amplifying stage carries out wide band amplitude amplification to signal independently in the claim 1, it has introduced DC restoration circuit, the synchronous top of signal is returned to a fixed level, thereby the dynamic range that defines input signal does not change with the variation of average weight, increase effective linear dynamic range of amplifier, guaranteed amplifier linear work still in bigger gain variation range.This carries out amplitude correction in just can be on a large scale, is suitable for the longer electric wire or the compensation of cable transmission loss.

7, said high frequency compensation level is formed with continuously adjustable laddering peaking network therebetween by isolating the emitter-follower of usefulness before and after two works in the claim 1, there is not feedback loop in the entire circuit, not reason closed loop phase shift and cause unsteadiness or parasitic oscillation in the compensation process.Inter-stage influenced each other before and after the front and back isolation level had also reduced.

8, said adjustable gain final stage output stage is the amplitude fading of compensation high frequency compensation level introducing and the power amplifier that 2-4 tunnel (deciding on concrete application scenario), 75 Ω impedances output is provided in the claim 1, it has the dynamic range that approaches supply power voltage, and its gain can be regulated on a large scale.

9, variable gain amplifying stage of being promoted to a higher rank in claim 1, claim 6 and the claim 8 and adjustable gain final stage output stage are all only made full-time signal amplification usefulness, do not propose cable transmission is carried out frequency compensated task to them, avoided the correlation between gain, the frequency adjustment, they all are operated in the utmost point broad frequency range, and bigger gain-adjusted scope is arranged.

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