CN101873453A - Automatic gain controller of composite video signal and control method thereof - Google Patents
Automatic gain controller of composite video signal and control method thereof Download PDFInfo
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Abstract
The invention discloses an automatic gain controller of composite video signal and a control method thereof. The automatic gain controller comprises an AFE, a characteristic value detection and controlled variable generation module, a CPU and a system bus. The appropriate amplitude and DC bias characteristic value which are convenient to measure are selected according to the characteristics of the video signal, and a characteristic value detection and generation method is designed; according to the available digital value control characteristics of a numerical control gain bias adjusting module in the AFE, a pure digital feedback control circuit is designed; through analyzing the correspondence of the detected characteristic value and the generated controlled variable, the rapid generation of the controlled variable is realized by utilizing a simple lookup table; according to the characteristics that the video amplitude has volatility and the numerical control gain bias adjusting module has high adjustment accuracy, an adjusting and maintaining strategy is designed; and a transmission method of a feedback controlled variable based on an SoC bus structure is realized. The invention has high-precision real-time regulation and maintains the video to be smooth, and increases the adaptability of a composite video decoder on nonstandard input analog composite video signal.
Description
Technical field
The invention belongs to TV, digital video image processing and Display Technique field, be specifically related to regulate automatically in a kind of composite video signal decoder the automatic gain controller of input analog composite video signal amplitude and the realization of control method.
Background technology
The input signal of composite video decoder derives from the analog composite video signal of different types of channels transmission.(crest voltage Vpp excursion is about 0V～2V) because the difference of source encoding and channel transfer characteristic, the signal amplitude of input composite video decoder alter a great deal.But AFE (Analog Front End-analog video front end) commonly used only supports the input signal of Vpp＜1V.Analog signal is strong excessively, and the digital signal amplitude that generates that can cause sampling is overflowed; Analog signal excessively a little less than, the digital signal amplitude that generates of can causing sampling is low excessively, does not make full use of available amplitude interval.The serious distortion of digital signal on brightness and color saturation that all will cause sampling and generate.
Control need detect in real time to signal amplitude to analog composite video signal amplitude automatic gain in the composite video signal decoder, but the amplitude of vision signal is closely related with its video content and coded system, its peak level can only reach at ad-hoc location, can't detect in real time and accurately, thereby need carefully choose suitable amplitude characteristic value as detection limit.Simultaneously, the quick variation of video source provides requirement to precision and the real-time that designs, and possibility also is provided, and making full use of the information of amplitude characteristic value and the character of numerical control gain bias adjusting module can control accurately.
Summary of the invention
At the existing problem of AFE commonly used, the invention provides a kind of gain controller and control method that can automatically adjust to the analog composite video signal amplitude.This controller can detect the characteristic quantity of input composite video signal on amplitude and direct current biasing in real time, by comparing with nominal value, the feedback control value of analog composite video signal direct current biasing after generation adjustment input analog composite video signal amplitude gain and the clamper, the numerical control gain bias adjusting module of control of video AFE inside, the effect that the digital composite video signal amplitude that the realization sampling generates does not change with the input analog composite video signal amplitude.
For reaching above purpose, the present invention takes following technical scheme to be achieved: a kind of automatic gain controller of composite video signal, it is characterized in that, and comprising: an analog video front-end A FE, characteristic value detects and the controlled quentity controlled variable generation module, CPU and system bus; Wherein: described analog video front-end A FE comprises a clamper module, a numerical control gain bias adjusting module, an analog-to-digital conversion module, and a synchronous signal extraction, clock generating module; Carry out the DC level clamper after the analog composite video signal AC coupled of clamper module with input, analog composite video signal after the clamper gains through the numerical control gain bias adjusting module and the adjusting of direct current biasing, be admitted to analog-to-digital conversion module and sample, generate digital composite video signal; Simultaneously, the analog composite video signal of input is sent into synchronizing signal extraction, clock generating module, output row field sync signal and clock signal; Described digital composite video signal, row field sync signal and clock signal are fed through characteristic value and detect and the controlled quentity controlled variable generation module; Described characteristic value detects and the controlled quentity controlled variable generation module comprises: an amplitude, offset features value detection sub-module, an error generate submodule, a controlled quentity controlled variable generates look-up table and a gain biasing keeps submodule; Wherein, amplitude, offset features value detection sub-module are carried out the detection of amplitude characteristic value and direct current biasing characteristic value in conjunction with row, field sync signal that AFE generates to the vision signal after the digitlization; Error generates amplitude that submodule obtains amplitude, offset features value detection sub-module and direct current biasing characteristic value and compares with the nominal value of video standard specifies, obtains the margin of error; Controlled quentity controlled variable generates look-up table with the address of this margin of error as look-up table, is generated controlled quentity controlled variable to gain biasing accordingly and keeps submodule; The gain biasing keeps submodule to comprise four different hold mode submodules and an adjustment submodule; The gain biasing keeps submodule by CPU and system bus, output FEEDBACK CONTROL amount is given the numerical control gain bias adjusting module among the analog video front-end A FE, realizes the adjusting to analog composite video signal direct current biasing after the analog video signal gain of input AFE and the clamper.
In the such scheme, described four different hold mode submodules, comprise that a standard state keeps submodule, the excessive off-rating of an input range keeps submodule, and the too small off-rating of an input range keeps a submodule and a standard and non-standard critical condition to keep submodule; Wherein, standard state keeps submodule, is used to keep and the amplitude and the direct current biasing characteristic value of input analog composite video signal can be adjusted to the situation that meets the corresponding video standard; The excessive off-rating of input range keeps submodule, is used for keeping to cross ambassador's numerical control gain bias adjusting module because of the input analog composite video signal amplitude and can't adjusts and satisfy the standard compliant situation of output signal; The too small off-rating of input range keeps submodule, is used for keeping because of the input analog composite video signal amplitude is too small the numerical control gain bias adjusting module being adjusted and satisfies the standard compliant situation of output signal; Standard and non-standard critical condition keep submodule, are used to handle the input analog composite video signal amplitude and are in because of the standard of threshold value division and the situation of non-standard critical zone.
A kind of auto gain control method of realizing composite video signal based on the automatic gain controller of aforementioned composite video signal, it is characterized in that, comprise the steps: step 1, CPU detects analog video front-end A FE and characteristic value and controlled quentity controlled variable generation module tax initiation parameter value through system bus, afterwards, row, the field sync signal of utilizing amplitude, offset features value detection sub-module to generate in conjunction with AFE are carried out amplitude characteristic value and the detection of direct current biasing characteristic value to the vision signal after the digitlization; Promptly by linage-counter being set in synchronous head top-composite video signal blanking interval crop or back porch position, ask for the weighted average of signal with the smooth region of synchronous head bottom, and then do that difference is tried to achieve the synchronous head range value and as the characteristic value of input analog composite video signal amplitude; Simultaneously, with the weighted average of the synchronous head of trying to achieve bottom smooth region signal as clamper after the characteristic value of direct current biasing of analog composite video signal; Step 2, amplitude characteristic value that detection is obtained and direct current biasing characteristic value compare generation amplitude and direct current biasing error with the nominal value of video standard specifies; In controlled quentity controlled variable generation look-up table, obtain the gain of these two error correspondences and the generation controlled quentity controlled variable of direct current biasing with error normalization and as index address; Step 3, gain biasing keeps the generation controlled quentity controlled variable of submodule by two error correspondences of receiving step two gained and the analog composite video signal amplitude of the input of step 1 gained, the characteristic value of analog composite video signal direct current biasing after the clamper, in four different hold mode submodules and an adjustment submodule, carry out logic determines respectively according to a state machine, when the analog composite video signal amplitude stabilization of input, export the feedback regulation amount of a stable gain and direct current biasing, CPU utilizes system bus to give the adjusting module of the numerical control gain bias among the AFE with this FEEDBACK CONTROL amount; When the analog composite video signal amplitude of input was unstable, the gain biasing kept submodule in time the numerical control gain bias adjusting module among the AFE to be regulated again in conjunction with the gain of two error correspondences and the generation controlled quentity controlled variable of direct current biasing; Step 4, repeated execution of steps two and step 3 are finished the continuous adjustment to analog composite video signal direct current biasing after input analog composite video signal amplitude and the clamper.
In the said method, the described gain biasing of step 3 keeps submodule to carry out logic determines respectively in four different hold mode submodules and an adjustment submodule according to a state machine, and export corresponding feedback regulation amount, its specific operation process is: when described state machine is operated in the adjustment submodule, earlier the fiducial value of adjusting is fed back to numerical control gain bias adjusting module among the AFE, to gain then and the generation controlled quentity controlled variable of direct current biasing feeds back to numerical control gain bias adjusting module among the AFE, direct current biasing to analog composite video signal after the amplitude of input analog composite video signal and the clamper is adjusted, adjusted amplitude and direct current biasing characteristic value compare with first threshold and judge, enter one of them state according to judged result and keep submodule, and preserve amplitude and the direct current biasing characteristic value of this moment; When described state machine is operated in any one hold mode submodule, the amplitude and amplitude and the direct current biasing characteristic value of direct current biasing characteristic value when entering this submodule of input is poor, when difference is not more than second threshold value, keep this hold mode submodule, keep entering this submodule FEEDBACK CONTROL amount constantly to the numerical control gain bias adjusting module among the AFE; During greater than second threshold value, enter the adjustment submodule and adjust.
The present invention sets the gain biasing and keeps the submodule initial time to be in adjustment submodule (also can be set in arbitrary maintenance submodule).CPU and system bus are brought in constant renewal in the FEEDBACK CONTROL amount and are given numerical control gain bias adjusting module among the AFE, finish the adjustment to analog composite video signal direct current biasing after input analog composite video signal amplitude and the clamper.
Characteristics of the present invention are to take into full account the video amplitude feature, the amplitude and the direct current biasing characteristic value that are suitable for detecting have been chosen, the advantage that the digital control amount of combining with digital control gain controlling adjustment circuit is easy to generate, utilize Design of Digital Circuit to realize the simulation amplifier control of complexity, obtain characteristic value and generate mapping relations between controlled quentity controlled variable by look-up table, utilize simple structure to solve and generate the requirement that controlled quentity controlled variable is tried to achieve fast, SoC (SOC (system on a chip)) design has been considered in the transmission of FEEDBACK CONTROL amount in addition, has proposed the controlled quentity controlled variable feedback system based on bus.
Compared with the prior art, advantage of the present invention is: 1. the synchronous head feature that has taken into full account digital composite video signal, choose the amplitude and the direct current biasing characteristic value that are suitable for detecting, thereby avoided complicated statistical calculation, under the condition that keeps precision, simplified circuit design; 2. utilize the numerical control gain control circuit that the input analog signal is controlled, make complicated analog circuit control problem be reduced to the Design of Digital Circuit problem, reached the effect of simplified design difficulty; 3. utilize amplitude and the direct current biasing characteristic value choose to generate simple mapping relations between the controlled quentity controlled variable, finished the generation of controlled quentity controlled variable, simplified circuit design, improved FEEDBACK CONTROL speed by look-up table configuration with sum of errors between standard value; 4. in conjunction with video standard, and by experiment in advance, after having chosen various input source adjustment and finishing, the reasonable threshold value that gain and direct current biasing controlled quentity controlled variable remain unchanged.Both guarantee the continuity of vision signal, controlled adjustment when carrying out the bigger change of input analog composite video signal amplitude during postscript timely; 5. considered to be integrated in the design feature of SoC chip, proposed the circuit structure that the FEEDBACK CONTROL amount utilizes system bus to transmit, helped the integrated difficulty of simplified system as embedded IP, and can be in the configuration between each resource of system-level optimization.
Description of drawings
The present invention is described in further detail below in conjunction with accompanying drawing.
Fig. 1 is an automatic gain controller structured flowchart of the present invention.
Fig. 2 is the structured flowchart that controlled quentity controlled variable generates look-up table among Fig. 1.
Fig. 3 is the concrete structure block diagram that the gain biasing keeps submodule among Fig. 1.
Fig. 4 is the input video state of the corresponding submodule correspondence of Fig. 3.
Fig. 5 is each submodule state transition diagram among Fig. 3.
Fig. 6 is a state transition diagram of adjusting submodule among Fig. 3.
Embodiment
Referring to Fig. 1, be depicted as the overall construction drawing of automatic gain controller of the present invention, the operation principle of whole composite video signal automatic gain controller has been described.Analog composite video signal is after AC coupled enters AFE, and one road input sync signal extracts, clock generating module generates row field sync signal and clock signal; Another road is through the clamper module, and generating with the clamping level is the analog composite video signal of reference level, passes through numerical control gain bias adjusting module (PGA) then the amplitude and the direct current biasing of this analog composite video signal are adjusted.Adjusted analog composite video signal is sampled through analog-to-digital conversion module (ADC), and sampling clock is that synchronizing signal is extracted, the clock signal of clock generating module output.The sampling back generates digital composite video signal.
The digital composite video signal of AFE output, row field sync signal and clock signal are sent into amplitude, the offset features value detection sub-module in characteristic value detection and the controlled quentity controlled variable generation module.It detects the amplitude and the direct current biasing of synchronous head in the digital composite video signal.Detection method is by the weighted average that linage-counter (calculating the counter of every capable pixel number) is asked for signal respectively at the top (composite video signal blanking interval crop or back porch position) and the smooth region bottom the synchronous head of synchronous head is set.It is poor that the weighted average of these two signals is done, and difference is as the characteristic value of input analog composite video signal amplitude; With the weighted average of the synchronous head of trying to achieve bottom smooth region signal as clamper after the characteristic value of direct current biasing of analog composite video signal.
Error in the amplitude that generates and detection of direct current biasing characteristic value input feature vector value and the controlled quentity controlled variable generation module generates submodule.In this submodule, these two characteristic values are compared with the nominal value of its corresponding video standard respectively, do difference and try to achieve absolute error.(the high and low threshold value of amplitude characteristic value correspondence is 0 and-112 for the video standard TSC-system to the absolute error that obtains among the present invention, is 0 and-118 for the video standard Phase Alternation Line system with high and low two threshold values; The high and low threshold value of direct current biasing characteristic value correspondence is 1024 and 0 for two kinds of standards; These two threshold values are relevant with the adjusting range of numerical control gain bias adjusting module among the AFE, not absolute) relatively, and will be set at high threshold greater than the absolute error of high threshold, will be set at low threshold value less than the absolute error of low threshold value.After the result that aforesaid operations obtains carries out normalization, obtain the final margin of error.The margin of error among the present invention after the normalization of amplitude is by 7bits (7 binary system fixed-point numbers) expression, and the margin of error after the direct current biasing normalization is represented by 10bits (10 binary system fixed-point numbers).Here the bit wide of the margin of error is not absolute, and it is identical to generate the address signal length of look-up table with aftermentioned, if the address signal Design of length changes, also should adjust accordingly as the case may be herein.Parameters such as standard value that needs here and threshold value are by CPU process system bus assignment.
Error generates the normalization error of submodule output and imports as the address signal that the controlled quentity controlled variable in characteristic value detection and the controlled quentity controlled variable generation module generates look-up table.Controlled quentity controlled variable generates look-up table and is made of ROM, pre-deposits the data of each address correspondence, only needs can obtain the pre-deposit data of corresponding address in conjunction with clock Input Address signal.Generating look-up table with the controlled quentity controlled variable of the gain of TSC-system formula shown in Figure 2 is example (other composite video standard is approximate with it, tired stating).Pre-deposit the data of each address correspondence, and the controlled quentity controlled variable of the data represented gain here.Address is by being looked into gain controlling amount corresponding address in look-up table among the figure, and clock is a work clock, and q is the controlled quentity controlled variable of the gain of output.As previously mentioned, the normalization margin of error of the amplitude of the 7bits that obtains is generated the address signal of look-up table as the gain controlling amount, and in conjunction with the clock input, dateout is the controlled quentity controlled variable of the gain of the normalization margin of error correspondence of input.Profit uses the same method and can obtain the controlled quentity controlled variable of the direct current biasing that needs.Here with the gain controlling amount and the generation controlled quentity controlled variable of direct current biasing characteristic quantity called after gain and the generation controlled quentity controlled variable of direct current biasing that obtain.In addition, it may be noted that the value of look-up table is obtained by experiment, relevant with numerical control gain bias adjusting module character among the AFE.Look-up table address size and generation controlled quentity controlled variable bit wide are by the adjusting range decision of numerical control gain bias adjusting module design among the AFE.As previously mentioned, in case look-up table address size design herein changes, error generates the bit wide of the margin of error of submodule output and also should adjust.Simultaneously, Xiang Guan parameters such as look-up table value by CPU through the system bus assignment.
As shown in Figure 3, generation controlled quentity controlled variable and amplitude, the amplitude of offset features value detection sub-module output and the gain biasing in detection of direct current biasing characteristic value input feature vector value and the controlled quentity controlled variable generation module that controlled quentity controlled variable generates look-up table output keep submodule, and this submodule is made of five submodules.Be respectively standard state and keep submodule, the excessive off-rating of input range keeps submodule, and the too small off-rating of input range keeps submodule, and standard and non-standard critical condition keep submodule, and adjusts submodule.These five submodules constitute a state machine, work in these five submodules respectively according to the saltus step condition.
Wherein standard state keeps submodule, is used to keep input analog composite video signal to be adjusted into the situation of standard state; The excessive off-rating of input range keeps submodule, is used for keeping to cross ambassador AFE numerical control gain bias adjusting module because of the input analog composite video signal amplitude and can't adjusts and satisfy the standard compliant situation of output signal; The too small off-rating of input range keeps submodule, is used for keeping can't adjusting because of the too small AFE of the making numerical control gain bias of input analog composite video signal amplitude adjusting module satisfying the standard compliant situation of output signal; Standard and non-standard critical condition keep submodule, are used to handle the situation that the input analog composite video signal amplitude is in standard and off-rating critical zone; Adjust submodule and be implemented in when the Analog Composite Video direct current biasing changes after input Analog Composite Video amplitude or the clamper situation about need adjust again.
When above-mentioned state machine is operated in above-mentioned arbitrary hold mode submodule, adjust the FEEDBACK CONTROL amount of exporting to numerical control gain bias adjusting module among the AFE that submodule is asked for before preserving amplitude and the direct current biasing characteristic value when entering this submodule and entering this module; And constantly ask for the amplitude of current input and direct current biasing characteristic value with preserve enter this submodule the time amplitude and the difference between the direct current biasing characteristic value.When the difference d that asks for satisfies d＜y or d=y when (y is called second threshold value, is taken as 10 among the present invention), with preserve enter this hold mode submodule before adjust the FEEDBACK CONTROL amount output of giving numerical control gain bias adjusting module among the AFE that submodule is asked for.When the difference d that asks for satisfies d＞y, jump out this hold mode submodule and enter the adjustment submodule.
When being operated in the adjustment submodule, as shown in Figure 4, in conjunction with the amplitude characteristic value a that imports the amplitude size of input analog composite video signal being carried out state and divide.By amplitude threshold a1, a2, a3, (0＜a1＜a2＜a3＜a4) marks off standard state (a2＜a＜a3 to a4, or a=a2 or a=a3), excessive off-rating (a＞the a4 of input range, or a=a4) and the too small off-rating (a＜a1 of input range, or a=a1) and critical condition 1 (a1＜a＜a2) and critical condition 2 (a3＜a＜a4, with critical condition 1 unified formation critical condition), be to adjust to enter to need the state handled respectively behind four different hold mode submodules: when the amplitude of judging input analog composite video signal is in standard state, adjusts and jump to standard state behind the submodule end-of-job and keep submodule work.Accordingly, when the amplitude of input analog composite video signal is in the excessive off-rating of input range, the too small off-rating of input range and critical condition, jump to the excessive off-rating maintenance of input range submodule after adjusting the submodule end-of-job, the too small off-rating of input range keeps submodule, and standard and non-standard critical condition keep submodule.In addition, adjust submodule, constituted five states in the worker state machine in the gain biasing maintenance submodule jointly, as shown in Figure 5 corresponding to the adjustment state.
As shown in Figure 6, the working method of adjusting submodule can be represented by a state machine.The other4states state is unified the one of four states except that the adjustment state in the presentation graphs 5 among the figure.This one of four states Shi Douhui that can't maintain the original state skips to the adjustment state.Adjustment state inside is made of a group state machine.After adjusting beginning, state machine at first enters the response of wait0 state waiting system bus; Entering the controlled quentity controlled variable that the setting of set_7f00 attitude feeds back to the gain of numerical control gain bias adjusting module among the AFE afterwards is 511, and the controlled quentity controlled variable of direct current biasing is 0 (to correspond respectively to the fiducial value that minimum gain controlling amount and maximum direct current biasing controlled quentity controlled variable are called adjustment among the present invention.Concrete numerical value is adjusted the circuit design decision by numerical control gain bias, and is not absolute); And enter the wait1 state, be performed to guarantee the FEEDBACK CONTROL amount that bus has a gain that enough response times are provided with before guaranteeing; Enter the gain_count state then, receive the generation controlled quentity controlled variable of gain this moment and the FEEDBACK CONTROL amount output of conduct gain; Guarantee that at the wait2 state this controlled quentity controlled variable is fed numerical control gain bias adjusting module to the AFE; Enter the detect_gain state again, between record amplitude characteristic value location at this moment: nominal value range, by closed interval [t2, t3] represent (corresponding to aforesaid standard state, adjust and finish to jump to standard state maintenance submodule), be slightly larger than or be slightly less than nominal value range, respectively by open interval (t1, t2) and (t3, t4) expression is (corresponding to critical condition, adjust and finish the standard that jumps to and non-standard critical condition maintenance submodule), less than nominal value range, by closed interval [0, t1] represent (corresponding to the too small off-rating of input range, adjust and finish to jump to the too small off-rating maintenance of input range submodule), greater than nominal value range, by closed interval [t4,1023] expression is (corresponding to the excessive off-rating of input range, adjust and finish to jump to the excessive off-rating maintenance of input range submodule), here the amplitude characteristic value is shown (by analog-to-digital conversion module output signal bit wide decision among the AFE by 10 2 system numerical tables, not absolute), and 0＜t1＜t2＜t3＜t4＜1023, t1, t2, t3 and t4 unify the called after first threshold; Enter the offset_count state afterwards, receive the generation controlled quentity controlled variable of direct current biasing this moment and as the FEEDBACK CONTROL amount output of direct current biasing; Guarantee that at the wait3 state this FEEDBACK CONTROL amount is performed; Enter the jump state at last,, jump to corresponding hold mode submodule according in the detect_gain state before between amplitude characteristic value location.
At last, as shown in Figure 1, the gain biasing keeps submodule output FEEDBACK CONTROL amount, via the CPU scheduling, feeds back to numerical control gain adjusting module among the AFE by bus, finishes whole closed-loop system.Simultaneously, aforesaid AFE and characteristic value detect and the controlled quentity controlled variable generation module in the initiation parameter value also by CPU through the system bus assignment.
The unanimity of partly setting forth with summary of the invention, in conjunction with aforesaid automatic gain controller each concrete Module Design scheme and operation principle, can obtain the auto gain control method of following composite video signal: step 1: at first, CPU detects analog video front-end A FE and characteristic value and controlled quentity controlled variable generation module tax initiation parameter value through system bus.
Secondly, after AC coupled entered AFE, one road input sync signal extracted, clock generating module generates row field sync signal and clock signal with analog composite video signal; Another road is through the clamper module, and generating with the clamping level is the analog composite video signal of reference level, through the numerical control gain bias adjusting module amplitude and the direct current biasing of this analog composite video signal is adjusted then.Adjusted analog composite video signal is sampled through the analog-to-digital conversion module, and sampling clock is that synchronizing signal is extracted, the clock signal of clock generating module output.The sampling back generates digital composite video signal.The digital composite video signal of output, row field sync signal and clock signal are sent into amplitude, the offset features value detection sub-module in characteristic value detection and the controlled quentity controlled variable generation module.It detects the amplitude and the direct current biasing of synchronous head in the digital composite video signal.Detection method is by the weighted average that linage-counter is asked for signal respectively at the top (composite video signal blanking interval crop or back porch position) and the smooth region bottom the synchronous head of synchronous head is set.The difference of the weighted average of these two signals is as the characteristic value of input analog composite video signal amplitude; The weighted average of the synchronous head of trying to achieve bottom smooth region signal as clamper after the characteristic value of direct current biasing of analog composite video signal.
Step 2: at first, amplitude characteristic value and direct current biasing characteristic value error originated from input that detection is obtained generate submodule.In this submodule, these two characteristic values are compared with the nominal value of its corresponding video standard respectively, do difference and try to achieve absolute error.The absolute error that obtains with before described high and low two threshold ratios, and will be set at high threshold greater than the absolute error of high threshold, will be set at low threshold value less than the absolute error of low threshold value.Result behind the aforesaid operations carries out normalization, obtains the normalized margin of error.
Secondly, the normalization margin of error of amplitude is imported the generation controlled quentity controlled variable that just can be gained accordingly as the address signal that the gain controlling amount generates look-up table in conjunction with clock.Profit uses the same method and can obtain the generation controlled quentity controlled variable of the direct current biasing that needs, and export to the biasing maintenance submodule step 3 that gains: the analog composite video signal amplitude that the biasing maintenance submodule that gains is imported by the generation controlled quentity controlled variable and the step 1 gained of two error correspondences of receiving step two gained, the characteristic value of analog composite video signal direct current biasing after the clamper, in four different hold mode submodules and an adjustment submodule, carry out logic determines respectively according to a state machine, when the analog composite video signal amplitude stabilization of input, export the feedback regulation amount of a stable gain and direct current biasing, CPU utilizes system bus to give the adjusting module of the numerical control gain bias among the AFE with this FEEDBACK CONTROL amount; When the analog composite video signal amplitude of input was unstable, the gain biasing kept submodule in time the numerical control gain bias adjusting module among the AFE to be regulated again in conjunction with the generation controlled quentity controlled variable of gain and direct current biasing.
Step 4: repeated execution of steps two and step 3, finish continuous adjustment to analog composite video signal direct current biasing after input analog composite video signal amplitude and the clamper.
In the said method, the described gain biasing of step 3 keeps submodule to carry out logic determines respectively in four different hold mode submodules and an adjustment submodule according to a state machine, and export corresponding feedback regulation amount, its specific operation process is: when described state machine is operated in the adjustment submodule, earlier the fiducial value of adjusting is fed back to numerical control gain bias adjusting module among the AFE, to gain then and the generation controlled quentity controlled variable of direct current biasing feeds back to numerical control gain bias adjusting module among the AFE, direct current biasing to analog composite video signal after the amplitude of input analog composite video signal and the clamper is adjusted, adjusted amplitude and direct current biasing characteristic value compare with first threshold and judge, enter one of them state according to judged result and keep submodule, and preserve amplitude and the direct current biasing characteristic value of this moment; When described state machine is operated in any one hold mode submodule, adjust the FEEDBACK CONTROL amount of exporting to numerical control gain bias adjusting module among the AFE that submodule is asked for before preserving amplitude and the direct current biasing characteristic value when entering this submodule and entering this module; And the direct current biasing characteristic value of constantly asking for analog composite video signal after the amplitude of current input analog composite video signal and the clamper is with amplitude of preserving and the difference between the direct current biasing characteristic value.When the difference of asking for is not more than second threshold value, export the FEEDBACK CONTROL amount of exporting to numerical control gain bias adjusting module among the AFE that the preceding adjustment of this hold mode submodule submodule is asked for that enters of preserving.When the difference of asking for during, jump out this hold mode submodule and enter the adjustment submodule greater than second threshold value.
In above-mentioned steps three concrete operations, the concrete workflow of the adjustment submodule of mentioning is made of a state machine.After four different maintenance submodules were jumped into the adjustment submodule, this state machine at first entered the response of wait0 state waiting system bus; Enter gain controlling amount that the setting of set_7f00 attitude feeds back to numerical control gain bias adjusting module among the AFE afterwards for minimum, the direct current biasing controlled quentity controlled variable be a maximum (fiducial value of adjustment); And enter the wait1 state and wait for, guarantee that bus has the FEEDBACK CONTROL amount that enough response times guarantee the gain of set_7f00 attitude setting and is performed; Enter the gain_count state then, receive the generation controlled quentity controlled variable (corresponding to the generation controlled quentity controlled variable of the amplitude characteristic value of the analog composite video signal of input this moment) of gain this moment and as the FEEDBACK CONTROL amount output of gain; Guarantee that at the wait2 state this FEEDBACK CONTROL amount is fed that the numerical control gain bias adjusting module carries out the amplitude adjustment to the AFE; Enter the detect_gain state again, between record amplitude characteristic value location at this moment, it is aforesaid nominal value range, be slightly larger than or be slightly less than nominal value range, less than nominal value range, greater than one in the nominal value range, four the hold mode submodules (concrete corresponding relation as described above) that enter after adjustment is finished have been characterized; Enter the offset_count state afterwards, receive the generation controlled quentity controlled variable of direct current biasing this moment and as the FEEDBACK CONTROL amount output of direct current biasing; Guarantee that at the wait3 state this FEEDBACK CONTROL amount is performed; Enter the jump state at last,, jump to corresponding hold mode submodule according in the detect_gain state before between amplitude characteristic value location.
Claims (4)
1. the automatic gain controller of a composite video signal is characterized in that, comprising: an analog video front-end A FE, and characteristic value detects and the controlled quentity controlled variable generation module, CPU and system bus;
Wherein: described analog video front-end A FE comprises a clamper module, a numerical control gain bias adjusting module, an analog-to-digital conversion module, and a synchronous signal extraction, clock generating module; Carry out the DC level clamper after the analog composite video signal AC coupled of clamper module with input, analog composite video signal after the clamper gains through the numerical control gain bias adjusting module and the adjusting of direct current biasing, be admitted to analog-to-digital conversion module and sample, generate digital composite video signal; Simultaneously, the analog composite video signal of input is sent into synchronizing signal extraction, clock generating module, output row field sync signal and clock signal; Described digital composite video signal, row field sync signal and clock signal are fed through characteristic value and detect and the controlled quentity controlled variable generation module;
Described characteristic value detects and the controlled quentity controlled variable generation module comprises: an amplitude, offset features value detection sub-module, an error generate submodule, a controlled quentity controlled variable generates look-up table and a gain biasing keeps submodule; Wherein, amplitude, offset features value detection sub-module are carried out the detection of amplitude characteristic value and direct current biasing characteristic value in conjunction with row, field sync signal that AFE generates to the vision signal after the digitlization; Error generates amplitude that submodule obtains amplitude, offset features value detection sub-module and direct current biasing characteristic value and compares with the nominal value of video standard specifies, obtains the margin of error; Controlled quentity controlled variable generates look-up table with the address of this margin of error as look-up table, is generated controlled quentity controlled variable to gain biasing accordingly and keeps submodule; The gain biasing keeps submodule to comprise four different hold mode submodules and an adjustment submodule; The gain biasing keeps submodule by CPU and system bus, output FEEDBACK CONTROL amount is given the numerical control gain bias adjusting module among the analog video front-end A FE, realizes the adjusting to analog composite video signal direct current biasing after the analog video signal gain of input AFE and the clamper.
2. the automatic gain controller of composite video signal as claimed in claim 1, it is characterized in that, described four different hold mode submodules, comprise that a standard state keeps submodule, the excessive off-rating of one input range keeps submodule, and the too small off-rating of an input range keeps a submodule and a standard and non-standard critical condition to keep submodule;
Wherein, standard state keeps submodule, is used to keep and the amplitude and the direct current biasing characteristic value of input analog composite video signal can be adjusted to the situation that meets the corresponding video standard;
The excessive off-rating of input range keeps submodule, is used for keeping to cross ambassador's numerical control gain bias adjusting module because of the input analog composite video signal amplitude and can't adjusts and satisfy the standard compliant situation of output signal;
The too small off-rating of input range keeps submodule, is used for keeping because of the input analog composite video signal amplitude is too small the numerical control gain bias adjusting module being adjusted and satisfies the standard compliant situation of output signal;
Standard and non-standard critical condition keep submodule, are used to handle the input analog composite video signal amplitude and are in because of the standard of threshold value division and the situation of non-standard critical zone.
3. the auto gain control method of a composite video signal is realized based on the automatic gain controller of claim 1 composite video signal, it is characterized in that, comprises the steps:
Step 1, CPU detects analog video front-end A FE and characteristic value and controlled quentity controlled variable generation module tax initiation parameter value through system bus, afterwards, row, the field sync signal of utilizing amplitude, offset features value detection sub-module to generate in conjunction with AFE are carried out amplitude characteristic value and the detection of direct current biasing characteristic value to the vision signal after the digitlization; Promptly by linage-counter being set in synchronous head top-composite video signal blanking interval crop or back porch position, ask for the weighted average of signal with the smooth region of synchronous head bottom, and then do that difference is tried to achieve the synchronous head range value and as the characteristic value of input analog composite video signal amplitude; Simultaneously, with the weighted average of the synchronous head of trying to achieve bottom smooth region signal as clamper after the characteristic value of direct current biasing of analog composite video signal;
Step 2, amplitude characteristic value that detection is obtained and direct current biasing characteristic value compare generation amplitude and direct current biasing error with the nominal value of video standard specifies; In controlled quentity controlled variable generation look-up table, obtain the gain of these two error correspondences and the generation controlled quentity controlled variable of direct current biasing with error normalization and as index address;
Step 3, gain biasing keeps the generation controlled quentity controlled variable of submodule by two error correspondences of receiving step two gained and the analog composite video signal amplitude of the input of step 1 gained, the characteristic value of analog composite video signal direct current biasing after the clamper, in four different hold mode submodules and an adjustment submodule, carry out logic determines respectively according to a state machine, when the analog composite video signal amplitude stabilization of input, export the feedback regulation amount of a stable gain and direct current biasing, CPU utilizes system bus to give the adjusting module of the numerical control gain bias among the AFE with this FEEDBACK CONTROL amount; When the analog composite video signal amplitude of input was unstable, the gain biasing kept submodule in time the numerical control gain bias adjusting module among the AFE to be regulated again in conjunction with the generation controlled quentity controlled variable of two error correspondences;
Step 4, repeated execution of steps two and step 3 are finished the continuous adjustment to analog composite video signal direct current biasing after input analog composite video signal amplitude and the clamper.
4. the auto gain control method of composite video signal as claimed in claim 3, it is characterized in that, in the step 3, described gain biasing keeps submodule to carry out logic determines respectively in four different hold mode submodules and an adjustment submodule according to a state machine, and export corresponding feedback regulation amount, its concrete operations are:
When described state machine is operated in the adjustment submodule, earlier the fiducial value of adjusting is fed back to numerical control gain bias adjusting module among the AFE, to gain then and the generation controlled quentity controlled variable of direct current biasing feeds back to numerical control gain bias adjusting module among the AFE, direct current biasing to analog composite video signal after the amplitude of input analog composite video signal and the clamper is adjusted, adjusted amplitude and direct current biasing characteristic value compare with first threshold and judge, enter one of them state according to judged result and keep submodule, and preserve amplitude and the direct current biasing characteristic value of this moment;
When described state machine is operated in any one hold mode submodule, the amplitude and amplitude and the direct current biasing characteristic value of direct current biasing characteristic value when entering this submodule of input is poor, when difference is not more than second threshold value, keep this hold mode submodule, keep entering this submodule FEEDBACK CONTROL amount constantly to the numerical control gain bias adjusting module among the AFE; During greater than second threshold value, enter the adjustment submodule and adjust.
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