CN1921576A - Activator for digital-analog compatible television transmitter - Google Patents
Activator for digital-analog compatible television transmitter Download PDFInfo
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- CN1921576A CN1921576A CN 200610091478 CN200610091478A CN1921576A CN 1921576 A CN1921576 A CN 1921576A CN 200610091478 CN200610091478 CN 200610091478 CN 200610091478 A CN200610091478 A CN 200610091478A CN 1921576 A CN1921576 A CN 1921576A
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Abstract
The invention relates to a television emitter activator, which uses digit technique to process pre-distortion correction. Wherein, when used in digit television emitter, only needs to change the ATV code plate into DTV code plate. The invention mainly comprises general ARM processor, programmable logic deice (FPGA), programmable frequency changer and D/A converter. The invention is based on software wireless structure, to divide the system into three layers as interface layer, setting layer and processing layer. The invention can improve the working quality of television emitter.
Description
Technical field
The present invention relates to the television transmitter exciter, adopt a kind of brand-new design philosophy and software approach, realize its in television transmitter the predistortion correction function that should possess.It both can be applicable to the simulated television transmitter, also can apply in the digital TV transmitter, adopted digital technology to carry out the exciter design of predistortion correction.The described the present invention of being mainly applies to the embodiment of simulated television transmitter; When applying to digital TV transmitter, only need to change the ATV encoding board into the DTV encoding board, just can be in Digital Television, for harassing the various distortions that (ISI) measures apart from (Shoulder Distance) and intersymbol with intermodulation (IMD) and shoulder, carry out precorrection and handle, thus the compatibility of this project of realization simulated television/Digital Television on using.This project promotes on the level and the gap between shortening and the developed country of China's television transmitter for the craftmanship of improving television transmitter, has very unique positive effect.
Background technology
Traditional analog driver in the television transmitter, generally form by institutes such as intermediate frequency modulator and frequency mixer, PLL circuit, surface acoustic wave (SAW) filter and frequency response devices, the circuit complexity, cost is higher, adjust to be difficult for, but and its predistortion correction is difficult to the signal quality that reaches desired.
The traditional analog driver of television transmitter is to the process of signal processing, it generally is the video of earlier television operating center being sent here, audio analog signals carries out suitable processing, just directly be modulated on intermediate frequency vision carrier frequency 38MHz and the sound carrier frequency 31.50MHz respectively then, and the modulated image intermediate frequency signal and the modulated accompanying sound intermediate frequency signal of output nominal level, modulated afterwards image intermediate frequency signal, pass through vestigial sideband Filtering Processing and group delay correction again, phase nonlinear is proofreaied and correct, the precorrection of the various numerous and diverse analog circuits of multiple tracks such as amplitude non-linearity correction is handled, and again the intermediate frequency modulated wave that intermediate frequency modulator produced is carried out frequency translation at last and is amplified to certain power to promote the unit of final power amplifier work.
And predistortion correction processing method of the present invention, then at first be that video, the audio frequency TV signal of simulation are converted to the digital quadrature baseband signal after digital processing, afterwards digital digital orthogonal baseband signal is carried out equilibrium and precorrection, convert analog baseband signal then to, directly be modulated at needed radio frequency carrier frequency point and go up and deliver to Power Amplifier Unit and amplify and broadcast thereby deliver to modulator again.
Adopt the basic thought of software radio SDR (Software Radio/Software-Defined Radio) in realization: construct one and have opening, standardization, modular general hardware platform, various functions are finished with software.This is a kind of brand-new thought, and it is once proposing just to be subjected to attention widely.So-called software radio (Software Defined Radio, be called for short SDR), adopt Digital Signal Processing exactly, on the general hardware platform of control able to programme, utilize software to define the each several part function that realizes radio station: to comprise Base-Band Processing of front end reception, intermediate frequency process and signal or the like.Be that whole radio station is all finished by software programming up to the control protocol part from high frequency, intermediate frequency, base band.Its core concept is to use " digital-to-analog " transducer in broadband in the place of as close as possible antenna, finishes the digitlization of signal as soon as possible, thereby makes the function of radio station define and realize with software as much as possible.
We adopt the method for designing that programming device and dedicated devices combine and the design philosophy of layering, design the exciter based on software radio.
Adopt figure adjustment and directly modulation, make divider chain simplify, need not intermediate frequency modulator and frequency mixer, PLL circuit, surface acoustic wave (SAW) filter and frequency response device.The benefit of bringing thus is: improved signal quality; Improved the stability of equipment; Need not complicated adjustment; Reduced cost.
Summary of the invention
In view of the foregoing, the objective of the invention is to, for the television transmitter exciter provides a brand-new design based on digital technology:
The overall plan block diagram as shown in Figure 1.
The main devices that system uses has four: general arm processor, programmable logic device (FPGA), frequency converter able to programme and D/A converter.Two main chip wherein: general arm processor and FPGA are the general programmable device.Like this, when system design, exist the functional definition problem of general-purpose device.For the function that makes system is reasonably distributed between device, fully, effectively utilize resources of chip, and make system design simple, clear, on the basis of software radio architecture, adopt the method for designing of layering, the structure of system has been divided into three layers: interface layer, configuration layer and processing layer.
1, interface layer: be used for communicating by letter control whole system operation pattern with extraneous.Interface adopts the Ethernet interface of ARM.Peripheral control unit shown in the figure is a PC, and promptly the parallel port of PC links to each other with the Ethernet interface of ARM and communicates by letter, and the Control Parameter of system works pattern is passed to ARM.It may be noted that: device or the instrument with the Ethernet interface communication mode all can replace PC, the mode of operation of control system arbitrarily.
2, configuration layer: be used for finishing by ARM to the processing layer configuration parameter.The Control Parameter that ARM receives according to its Ethernet interface is called corresponding program, calculates needed each parameter value of configuration layer, and produces corresponding clock signal, and result of calculation is disposed to programmable device FPGA and frequency converter.
3, processing layer: form by FPGA, frequency converter and D/A converter.After the parameter configuration of FPGA and frequency converter was intact, processing layer broke away from configuration layer and works independently.Produce corresponding specific bit stream, the I of specific modulation mode, Q signal by FPGA, and produce specific clock signal and I, Q signal are write digital up converter finish modulated process, by D/A converter digital signal is become the output of simulation modulated signal again.
Described activator for digital-analog compatible television transmitter is made up of following modules: encoder, equalizer, modulator and synthesizer; These modules interconnect by a motherboard, by a Switching Power Supply power supply.Display unit and little processing and control element (PCE) of advanced technology in digit driver, have also been disposed simultaneously; Exciter carries out communication contact by RS232 interface and outside, thereby makes television transmitter can realize remote measuring and controlling.Can carry out from dynamic(al) correction the technical indicator of television transmitter by the RS232 interface.
The operation principle of described activator for digital-analog compatible television transmitter is: the anolog TV signals of input through the A/D conversion, form digital i/q signal in the ATV encoder; Distortion at the back level compensates in digital corrector then, because the signal that will compensate is a digital form, can be as accurate as the magnitude of each bit; I/q signal after the compensation directly is modulated on the carrier wave of tranmitting frequency, the broadcast singal (analog television broadcast) that the process digital filter can obtain having the residual sideband characteristic.
The present invention only needs change the ATV encoding board into the DTV encoding board when being applied in the digital TV transmitter, just can realize from the upgrading of simulated television to Digital Television.
Described coder module has been accepted an analog video signal, because vision signal is simulated, it is continuous on the amplitude value not only, and also be continuous in time, make the analog video signal digitlization and realize time division multiplexing, at first will carry out discretization to analog video signal in time and handle, this process is the sample process of signal.
Sampling has become upward discrete pulse signal of time to analog video signal, but the amplitude of pulse remains simulation, also must carry out discretization and handle, and could finally represent with number.This will give up zero processing that rounds to amplitude, and this process is the quantification treatment of TV signal.
Analog video signal is after sampling, quantizing, and signal also is not a digital signal, need convert it to the digital coding pulse, and this process is exactly the coding of TV signal.
Like this, described coder module has at first just been finished digitized three steps of anolog TV signals: sampling, quantification, encoding process are transformed into the digital signal that digital coding is handled to analog video signal; This digital signal through the HILBERT conversion, has become two quadrature video baseband Q signal and video baseband I signal after handling according to selected standard.In this process, the vestigial sideband characteristic of signal forms simultaneously.Simulated audio signal is handled by identical standard simultaneously also through digitlization, and the data that obtain are two enterprising line frequency modulation of sound subcarrier.
Two sound subcarriers can be transformed into two sound accompaniment baseband Q signal and sound accompaniment baseband I signals that carry out quadrature modulation again with a digital signal.
Digitized video and audio baseband signal are delivered to presetter and are carried out precorrection.Encoder is supported different to look, audio mode.Encoder also comprises a microprocessor, and it can drive whole exciter, and communicates with CCU.As the peripheral hardware of microcontroller, also have a program storage, this just means, microprogram that exciter is all and software leave a place in, under the situation of not changing any hardware,, carry out the automatic adjustment and the software upgrading of technical indicator through serial line interface.
In the input signal of encoder, vision signal nominal input range both can be 0.7VPP/75 Ω, also can be 1VPP/75 Ω, and this can select at the enterprising line operate of display by microprocessor; The difference of the input range of video input signals maximum admissible and nominal input range is 50%, if input range is too low, vision signal may detect to come out, and perhaps can not obtain qualitative data.If input signal is too big, signal will be limited in the A/D transition period so, and the one-tenth branch in the signal suffers a loss.
Encoder is added to treated signal recombination time on the female opening connector of multicore of equalizer back, and four passages that have 14-bit resolution are used for ATV.At first two passages are used for the transmission of video-I and video-Q, and the audio frequency-I of other two passages and audio frequency-Q signal include acoustic information.The clock frequency of signal is delivered to PLL on the female opening connector of multicore, it makes internal clocking synchronous.The input clock ratio is 27MHz to ATV.Utilize FIR control FPGA, by double ATV, the 54MHz system clock of an internally-originated clock, this system clock synchronizing signal is delivered to input buffer.Control the digital signal that needs and be with communicating by letter of system controller for circuit, also carry through multi-core connector.
Composite video signal is added to the FPGA group time delay equalizer.The back also comprises the first order all-pass filter and five second order all-pass filters that are adapted at the high-frequency group delay equalization of a suitable low frequency group delay equalization, and each first order all-pass filter, each second order filter can both be revised amplitude-frequency characteristic.
In the ATV occasion, can compensate by all-pass filter in the group delay distortion of the looking of transmitter output/sound duplexer.The amplitude-frequency response of vision signal upper end scope can be strengthened or be weakened.Group time delay equalizer uses 27MHZ inter-sync system clock for this purpose.At the group time delay equalizer output, signal uses 54MHz switch clock sampling.
Described equalizer (presetter) is in order to proofread and correct because of different decay (being loss) and the phase differences that cause of frequency.
1, can correcting attenuation and frequency relation, be called " attenuation equalizer ";
2, can the phase calibration difference and being called of frequency relation " phase equalizer ".
Often need use equalizer at the cable television system back warp.Equalizer is serially connected in the circuit of amplifier usually, be for high frequency that balanced cable transmission causes, low frequency end signal attenuation is inconsistent is provided with.Because the attenuation characteristic of cable increases with the rising of frequency.Attenuation equalizer commonly used is called amplitude equalizer again.Generally form by elements such as coil, capacitor, resistors.The characteristic impedance of attenuation equalizer equals a definite value, its equilibrium value is that the decibel of attenuation is poor between the cable high and low frequency reference point, and the frequency characteristic of equalizer is just in time opposite with the cable frequency characteristic, but the low decay of frequency is big, the high decay of frequency is little, plays proportionality action with this opposite characteristic.Equalizer is also often made fritter printed board inserter structure, divides with the size of equilibrium quantity.
Described equalizer (presetter) is made up of group time delay equalizer and linear presetter.Correction is carried out on digitlization base band level.At dual channel mode, video and audio signal is proofreaied and correct respectively in linear presetter.And then deliver to modulator.
An analog or digital television transmitter is mainly by exciter, amplifier, and the signal synthesizer of output filter and output is formed.Though what exciter was exported is top undamaged signal,, after the parts follow-up through television transmitter, the quality of signals quilt is deterioration progressively.For economic reasons, amplifier is usually operated at the high efficiency state, and this can cause the nonlinear distortion of signal.This just means that the instantaneous gain of signal and phase place are the functions of amplitude.Like this, will produce parasitic frequency in the signal spectrum.
The restriction of transmitter output channel can cause the linear phase distortion at output amplitude-versus-frequency curve edge, and in simulated television, it can cause colored the variation and ghost image.Therefore the ATV equalizer must be arranged.
In the channel limiter, signal phase utilizes group time delay equalizer to carry out preemphasis, like this, at output filter or looking/distortion that causes in the radio frequency channel limit procedure of sound duplexer obtained compensation, the preemphasis recoverable amplifier distortion that linear equalizer is introduced, the two exercising result makes the quality of transmitter output signal obtain recovery.Equalizer is worked in the base band of signal, and signal transmits with digital I/Q standard in time-domain.Equalization function is carried out voluntarily and is for example used programmable ICS by FPGAS.When transmitter is provided with, is installed to appropriate software in the chip and goes.
When signal was further processed, new frequency content was three times in the signal highest frequency and produces linearly along with frequency is elevated to, so sampling rate increases, these signal components are launched with also needing linear equalization.Method by interpolation is transformed into 54MHz to clock frequency with four FIR filters---one in each passage---.These control the FPGA. that mixes with ATV by the FIR filter of FIR control, and before video and audio signal mixed, tone filter also was used to level match.After the data transfer rate conversion, composite video and audio signal are sent to linear equalizer.It forms balanced memory and ARM by FPGA.
Balanced memory is divided into two parts:
1, first is balanced vision signal, composite signal and the information that contains video amplifier inclination curvature characteristic, and various threshold values are taken as auxiliary quantity and calculate, and content comprises the moment angle between twinkling signal amplitude and I and the Q signal.
2, the information that comprises of second portion has, and as the slope of ATV-separate type audio frequency amplifier, needs to calculate various auxiliary quantities and restriction threshold values.
Output buffer passes through the signal of preemphasis to the D/A converter.Will provide four D/A conversion passages for binary channels, the structure of D/A conversion passage is identical.Each passage contains an isesaD/A converter, balance amplifier, antialiasing filter, output amplifier and measuring amplifier.Output amplifier is delivered to SMP connector after being installed in plate to the composite signal through preemphasis of analog form, further handles in the ATV modulator.The output that the four measuring composite signal is arranged in the module front is for the reference value of each D/A converter can critically be provided with, so have 1V nominal level accurately in all passages.
Described modulator block is to be used for direct quadrature modulation generation video and sound carrier.These signals filtered and amplify after, deliver to output stage.
Modulator also provides a radio frequency monitor, the video before its energy output driver output and the antenna and the test data of sound carrier.The output control of exciter and supervision are also via this paths.
Measurement numerical value on the antenna both had been used for monitoring, also was used for display video and sound carrier power.
Modulator contains two treatment channel, handles video carrier, another processing audio carrier wave for one.
Described synthesizer is that the two radio frequency programs (signal) that overlap above different frequency are mixed, and forms the device that radio frequency (signal) multi-channel programme of having a lot of social connections band is exported.In the cable television system front end, blender is the Distribution Center of system signal, promptly concentrates all multichannel radio signals through technical finesse at the blender input, at the blender output signal is exported again, is distributed to grid and the user that arrives.
The main technical requirements of blender:
1, operating frequency: if the then frequency of blender broadband type should satisfy the requirement of whole frequency band in the system.If the then frequency of blender channel type should satisfy each channel requirement of required mixing;
2, insert loss: it is the smaller the better always to wish to insert loss (insert and lose) during signal process passive network.The blender input power claims the access of blender to lose with the ratio of power output.Inserting loss represents with decibel usually.When representing with decibel, poor for input level decibels and output level decibels.It is different that different blenders inserts loss;
3, input and output impedance: for each interface in whole system all should mate, so the input of blender and output impedance all should be 75 Europe; Mutual isolation between the input, in the ideal case, when the arbitrary input of blender added signal, this signal can not appear in other input, and arbitrary input should not influence other inputs when open circuit or short circuit phenomenon are arranged yet.But certain influence is in fact always arranged.Under the situation of each end coupling, a certain input adds a signal, and this signal level that this signal level and other input occur poor is the mutual isolation between the blender input, generally with decibel representing.For different blenders different requirements is arranged, generally require greater than 20 decibels.
In the single channel scheme, the sound carrier passage can remove, because the design of two passages almost is identical.Baseband signal, be homophase (I) signal and quadrature (Q) signal,, be added to the I/Q modulator by a low pass filter that is contained in input, mix at this I signal and video carrier local frequency (phase place+45 °), Q signal and local frequency (phase place-45 °) mix simultaneously.Two local signals are before being added to blender, and their phase place and amplitude are through stabilized treatment.
After the mixing, two signals after the addition, are given radio frequency rf signal again in synthesizer.Because there are error in blender and synthesizer, so quadrature modulator was adjusted.Here the problem that also has a carrier suppressed adjusting: if quadrature modulation is desirable, residual carrier wave can be curbed fully, and the cross (talk) of frequency mixer still can produce carrier leak.
The amplitude that carrier leak is can be by adding an equivalence anti-phase and the carrier signal of phase place are eliminated.The production method of proofreading and correct carrier wave is: remedy voltage to one and be added on the baseband signal, with the RF on the display → RFOUT VIDEO/AUDIO → BIAS I/BIAS Q window, guarantee the residual constant of quadrature modulation, remain on about 65 ℃ with heater.After the adjusting, video carrier and sound carrier are exported with quadrature modulator.Under the situation of quadrature modulation, synthesizer produces the carrier frequency that forms video and sound carrier.The reference frequency of frequency synthesizer can be provided by built-in GPS receiver or external module.When transmitter broke down or be wrong, the emergency control loop that is positioned on the base plate can keep transmitter normally to move.And motherboard is to be used for connecting exciter module and central control unit CCU.
The major technology index comprises:
1, in-band intermodulation:
a)≥1kW：≤-50dB；
B)＜1kW and 〉=100W :≤-48dB;
c)＜100W：≤-46dB。
2, group delay---frequency characteristic according to the regulation of two of A, B among the 4.2.5 among the SJ/T 10351-93 (less than with equal not requiring of 30W).
3, the wave distortion of luminance signal (annotating: during≤100W, do not require):
A) field time waveform distortion (field tilt) :≤2%;
B) line time wave distortion (line tilt) :≤2%;
C) 2T sine squared pulse distortion (Kp) :≤2%.
4, because the amplitude distortion of the luminance signal that the luminance level difference causes: low-frequency luminance nonlinearity answers≤10%.
5, because the distortion of the carrier chrominance signal that the luminance level difference causes
6, the differential gain (DG):
A) greater than with equal 1kW :≤6%;
B) less than 1kW with greater than with equal 30W :≤8%;
C) less than 30W :≤12%.
7, the differential phase (DP):
A) greater than with equal 1kW :≤± 5 °;
B) less than 1kW with greater than with equal 30W :≤± 7 °;
C) less than 30W :≤± 12 °.
8, AF harmonic distortion (in 40Hz～15kHz scope):
A) greater than with equal 30W :≤1%;
B) less than 30W :≤2%.
Description of drawings
Fig. 1 is an overall plan block diagram of the present invention.
Fig. 2 is a correction work schematic diagram of the present invention.
Fig. 3 is the location drawing of product of the present invention in network system.
Fig. 4 is time system module map for program.
The relevant connection block diagram of Fig. 5 time system module for program.
Embodiment
This product is used for simulated television transmitter and digital TV transmitter.Be to connect the critical piece of network signal (digital signal or analog signal) to transmitter.The position of exciter in whole network system as shown in Figure 3.Separate the MIP frame from the TS stream that the SDH network comes at adapter, system server when delivering to, the time system server add local markers, the delay of signal calculated emission, and under the situation that does not reach time of delay, the data that arrive being cushioned.After waiting to arrive time of delay, just data are sent to exciter.If anolog TV signals just send the AV signal to exciter.If Digital Television just sends TS and flows to exciter.During program the system module by the program caching module, broadcast module synchronously and constitute, its formation and associated are met Fig. 4,5.The program caching module is mainly finished the storage of program; Broadcast the synchronous broadcast that module is mainly finished calculating, setting and the program of time-delay synchronously, the exciter module is finished the amplification in advance to signal.
On reality is used,, can select Digital Television exciter or simulated television exciter according to the transmitter demand of reality.
The above is preferred embodiment of the present invention only, and protection scope of the present invention is not limited thereto.Anyly all belong within the protection range of the present invention based on the equivalent transformation on the technical solution of the present invention.
Claims (3)
1, activator for digital-analog compatible television transmitter is characterized in that:
A) it is to adopt the method for designing that programming device and dedicated devices combine and the design philosophy of layering, the exciter that designs based on software radio SDR (Software Radio/Software-Defined Radio), the predistortion correction with the digital technology realization that it has comprises that group delay distortion correction, differential gain ditortion are proofreaied and correct, differential phase distortion is proofreaied and correct and intermodulation distortion is proofreaied and correct.Only need to change its ATV encoding board into the DTV encoding board, just can apply to digital TV transmitter.
B) described digital technology predistortion correction, be to use " analog/digital " transducer in broadband to finish the digitlization of signal after, define and realize predistortion correction again with software.
2, as the activator for digital-analog compatible television transmitter of claims 1, its composition comprises following modules: encoder, equalizer, modulator and synthesizer; These modules interconnect by a motherboard, by a Switching Power Supply power supply; Display unit and little processing and control element (PCE) of advanced technology in digit driver, have also been disposed simultaneously; Exciter carries out communication contact by RS232 interface and outside, thereby makes television transmitter can realize remote measuring and controlling.Can carry out from dynamic(al) correction the technical indicator of television transmitter by the RS232 interface.
3, as the activator for digital-analog compatible television transmitter of claims 1, it is characterized in that its operation principle and analog driver are diverse: the anolog TV signals of input through the A/D conversion, form digital i/q signal in the ATV encoder; Distortion at the back level compensates in digital corrector then, because the signal that will compensate is a digital form, can be as accurate as the magnitude of each bit; I/q signal after the compensation directly is modulated on the carrier wave of tranmitting frequency, the broadcast singal (analog television broadcast) that the process digital filter can obtain having the residual sideband characteristic.Adopt figure adjustment and directly modulation, make divider chain simplify, need not intermediate frequency modulator and frequency mixer, PLL circuit, surface acoustic wave (SAW) filter and frequency response device.The benefit of bringing thus is: improved signal quality; Improved the stability of equipment; Need not complicated adjustment; Reduced cost.Only need to change the ATV encoding board into the DTV encoding board, just can realize from the upgrading of simulated television to Digital Television.
A) claims 2 described encoders, it is characterized in that: coder module is accepted an analog video signal, because vision signal is simulated, it is continuous on the amplitude value not only, and also be continuous in time, make the analog video signal digitlization and realize time division multiplexing, at first will carry out discretization to analog video signal in time and handle, this process is the sample process of signal.
Sampling has become upward discrete pulse signal of time to analog video signal, but the amplitude of pulse remains simulation, also must carry out discretization and handle, and could finally represent with number.This will give up zero processing that rounds to amplitude, and this process is the quantification treatment of TV signal.
Analog video signal is after sampling, quantizing, and signal also is not a digital signal, need convert it to the digital coding pulse, and this process is exactly the coding of TV signal.
The coder module of digit driver has at first just been finished digitized three steps of anolog TV signals like this: sampling, quantification, encoding process are transformed into the digital signal that digital coding is handled to analog video signal; This digital signal through the HILBERT conversion, has become two quadrature video baseband Q signal and video baseband I signal after handling according to selected standard.In this process, the vestigial sideband characteristic of signal forms simultaneously.Simulated audio signal is handled by identical standard simultaneously also through digitlization, and the data that obtain are two enterprising line frequency modulation of sound subcarrier.
Two sound subcarriers can be transformed into two sound accompaniment baseband Q signal and sound accompaniment baseband I signals that carry out quadrature modulation again with a digital signal.
Digitized video and audio baseband signal are delivered to presetter.Encoder is supported different to look, audio mode.Encoder also comprises a microprocessor, and it can drive whole exciter, and communicates with CCU.As the peripheral hardware of microcontroller, also have a program storage, this just means, microprogram that exciter is all and software leave a place in, under the situation of not changing any hardware,, carry out the automatic adjustment and the software upgrading of technical indicator through serial line interface.
In the input signal of encoder, vision signal nominal input range both can be 0.7VPP/75 Ω, also can be 1VPP/75 Ω, and this can select at the enterprising line operate of display by microprocessor; The difference of the input range of video input signals maximum admissible and nominal input range is 50%, if input range is too low, vision signal may detect to come out, and perhaps can not obtain qualitative data.If input signal is too big, signal will be limited in the A/D transition period so, and the one-tenth branch in the signal suffers a loss.
Encoder is added to treated signal recombination time on the female opening connector of multicore of equalizer back, and four passages that have 14-bit resolution are used for ATV.At first two passages are used for the transmission of video-I and video-Q, and the audio frequency-I of other two passages and audio frequency-Q signal include acoustic information.The clock frequency of signal is delivered to PLL on the female opening connector of multicore, it makes internal clocking synchronous.The input clock ratio is 27MHz to ATV.Utilize FIR control FPGA, by double ATV, the 54MHz system clock of an internally-originated clock, this system clock synchronizing signal is delivered to input buffer.Control the digital signal that needs and be with communicating by letter of system controller for circuit, also carry through multi-core connector.
Composite video signal is added to the FPGA group time delay equalizer.The back also comprises the first order all-pass filter and five second order all-pass filters that are adapted at the high-frequency group delay equalization of a suitable low frequency group delay equalization, and each first order all-pass filter, each second order filter can both be revised amplitude-frequency characteristic.
In the ATV occasion, can compensate by all-pass filter in the group delay distortion of the looking of transmitter output/sound duplexer.The amplitude-frequency response of vision signal upper end scope can be strengthened or be weakened.Group time delay equalizer uses 27MHZ inter-sync system clock for this purpose.At the group time delay equalizer output, signal uses 54MHz switch clock sampling.
B) claims 2 described equalizers (presetter) is characterized in that proofreading and correct because of different decay (being loss) and the phase differences that cause of frequency.
1) can correcting attenuation and frequency relation, be called " attenuation equalizer ";
2) can the phase calibration difference and being called of frequency relation " phase equalizer ".
Often need use equalizer at the cable television system back warp.Equalizer is serially connected in the circuit of amplifier usually, be for high frequency that balanced cable transmission causes, low frequency end signal attenuation is inconsistent is provided with.Because the attenuation characteristic of cable increases with the rising of frequency.Attenuation equalizer commonly used is called amplitude equalizer again.Generally form by elements such as coil, capacitor, resistors.The characteristic impedance of attenuation equalizer equals a definite value, its equilibrium value is that the decibel of attenuation is poor between the cable high and low frequency reference point, and the frequency characteristic of equalizer is just in time opposite with the cable frequency characteristic, but the low decay of frequency is big, the high decay of frequency is little, plays proportionality action with this opposite characteristic.Equalizer is also often made fritter printed board inserter structure, divides with the size of equilibrium quantity.
Described equalizer (presetter) is made up of group time delay equalizer and linear presetter.Correction is carried out on digitlization base band level.At dual channel mode, video and audio signal is proofreaied and correct respectively in linear presetter.And then deliver to modulator.
An analog or digital television transmitter is mainly by exciter, amplifier, and the signal synthesizer of output filter and output is formed.Though what exciter was exported is top undamaged signal,, after the parts follow-up through television transmitter, the quality of signals quilt is deterioration progressively.For economic reasons, amplifier is usually operated at the high efficiency state, and this can cause the nonlinear distortion of signal.This just means that the instantaneous gain of signal and phase place are the functions of amplitude.Like this, will produce parasitic frequency in the signal spectrum.
The restriction of transmitter output channel can cause the linear phase distortion at output amplitude-versus-frequency curve edge, and in simulated television, it can cause colored the variation and ghost image.Therefore the ATV equalizer must be arranged.
In the channel limiter, signal phase utilizes group time delay equalizer to carry out preemphasis, like this, at output filter or looking/distortion that causes in the radio frequency channel limit procedure of sound duplexer obtained compensation, the preemphasis recoverable amplifier distortion that linear equalizer is introduced, the two exercising result makes the quality of transmitter output signal obtain recovery.Equalizer is worked in the base band of signal, and signal transmits with digital I/Q standard in time-domain.Equalization function is carried out voluntarily and is for example used programmable ICS by FPGAS.When transmitter is provided with, is installed to appropriate software in the chip and goes.
When signal was further processed, new frequency content was three times in the signal highest frequency and produces linearly along with frequency is elevated to, so sampling rate increases, these signal components are launched with also needing linear equalization.Method by interpolation is transformed into 54MHz to clock frequency with four FIR filters---one in each passage---.These control the FPGA that mixes with ATV by the FIR filter of FIR control, and before video and audio signal mixed, tone filter also was used to level match.After the data transfer rate conversion, composite video and audio signal are sent to linear equalizer.It forms balanced memory and ARM by FPGA.
Balanced memory is divided into two parts:
1) first is balanced vision signal, composite signal and the information that contains video amplifier inclination curvature characteristic, and various threshold values are taken as auxiliary quantity and calculate, and content comprises the moment angle between twinkling signal amplitude and I and the Q signal.
2) information that comprises of second portion has, and as the slope of ATV-separate type audio frequency amplifier, needs to calculate various auxiliary quantities and restriction threshold values.
Output buffer passes through the signal of preemphasis to the D/A converter.Will provide four D/A conversion passages for binary channels, the structure of D/A conversion passage is identical.Each passage contains an isesa D/A converter, balance amplifier, antialiasing filter, output amplifier and measuring amplifier.Output amplifier is delivered to SMP connector after being installed in plate to the composite signal through preemphasis of analog form, does further processing in the ATV modulator.The output that the four measuring composite signal is arranged in the module front is for the reference value of each D/A converter can critically be provided with, so have 1V nominal level accurately in all passages.
C) claims 2 described modulators is characterized in that its module is that direct quadrature modulation produces video and sound carrier.These signals filtered and amplify after, deliver to output stage.
Modulator also provides a radio frequency monitor, the video before its energy output driver output and the antenna and the test data of sound carrier.The output control of exciter and supervision are also via this paths.
Measurement numerical value on the antenna both had been used for monitoring, also was used for display video and sound carrier power.
Modulator contains two treatment channel, handles video carrier, another processing audio carrier wave for one.
D) claims 2 described synthesizers is characterized in that the radio frequency program (signal) of the different frequency that two covers are above mixes, and form the device that radio frequency (signal) multi-channel programme of having a lot of social connections band is exported, i.e. synthesizer (blender).In the cable television system front end, synthesizer is the Distribution Center of system signal, promptly concentrates all multichannel radio signals through technical finesse at the synthesizer input, at the synthesizer output signal is exported again, is distributed to grid and delivers to the user.
The main technical requirements of described blender:
1) operating frequency: if the then frequency of blender broadband type should satisfy the requirement of whole frequency band in the system.If the then frequency of blender channel type should satisfy each channel requirement of required mixing;
2) insert loss: it is the smaller the better always to wish to insert loss (insert and lose) during signal process passive network.The blender input power claims the access of blender to lose with the ratio of power output.Inserting loss represents with decibel usually.When representing with decibel, poor for input level decibels and output level decibels.It is different that different blenders inserts loss;
3) input and output impedance: for each interface in whole system all should mate, so the input of blender and output impedance all should be 75 Europe; Mutual isolation between the input, in the ideal case, when the arbitrary input of blender added signal, this signal can not appear in other input, and arbitrary input should not influence other inputs when open circuit or short circuit phenomenon are arranged yet.But certain influence is in fact always arranged.Under the situation of each end coupling, a certain input adds a signal, and this signal level that this signal level and other input occur poor is the mutual isolation between the blender input, generally with decibel representing.For different blenders different requirements is arranged, generally require greater than 20 decibels.
In the single channel scheme, the sound carrier passage can remove, because the design of two passages almost is identical.Baseband signal, be homophase (I) signal and quadrature (Q) signal,, be added to the I/Q modulator by a low pass filter that is contained in input, mix at this I signal and video carrier local frequency (phase place+45 °), Q signal and local frequency (phase place-45 °) mix simultaneously.Two local signals are before being added to blender, and their phase place and amplitude are through stabilized treatment.
After the mixing, radio frequency rf signal is given in two signal additions in synthesizer again.Because there are error in blender and synthesizer, so quadrature modulator was adjusted.Here the problem that also has a carrier suppressed adjusting: if quadrature modulation is desirable, residual carrier wave can be curbed fully, and the cross (talk) of frequency mixer still can produce carrier leak.
The amplitude that carrier leak is can be by adding an equivalence anti-phase and the carrier signal of phase place are eliminated.The production method of proofreading and correct carrier wave is: remedy voltage to one and be added on the baseband signal, with the RF on the display → RFOUT VIDEO/AUDIO → BIAS I/BIAS Q window, guarantee the residual constant of quadrature modulation, remain on about 65 ℃ with heater.After the adjusting, video carrier and sound carrier are exported with quadrature modulator.Under the situation of quadrature modulation, synthesizer produces the carrier frequency that forms video and sound carrier.The reference frequency of frequency synthesizer can be provided by built-in GPS receiver or external module.When transmitter broke down or be wrong, the emergency control loop that is positioned on the base plate can keep transmitter normally to move.And motherboard is to be used for connecting exciter module and central control unit CCU.
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