CN101330278B - Gain programmable vision buffer amplifier circuit with SAG compensation - Google Patents
Gain programmable vision buffer amplifier circuit with SAG compensation Download PDFInfo
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- CN101330278B CN101330278B CN200710057682XA CN200710057682A CN101330278B CN 101330278 B CN101330278 B CN 101330278B CN 200710057682X A CN200710057682X A CN 200710057682XA CN 200710057682 A CN200710057682 A CN 200710057682A CN 101330278 B CN101330278 B CN 101330278B
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Abstract
The invention relates to a programmable gain circuit with SAG compensation for a video frequency buffer amplifier. An operational amplifier U1 of the circuit is connected with the programmable gain circuit with feedback and SAG compensation, wherein, the output end of the operational amplifier U1 is connected with a resistance R4 and a capacitance C4; the resistance R4 is connected with a capacitance C5 of the operational amplifier U1; the capacitance C4 is connected with a resistance R5 and an output resistance R6; the resistance R5 is connected with the capacitance C5 and a resistance R8; and the resistance R8 is connected with an equivalent resistance R7 of the programmable gain circuit. Compared with the circuit of the conventional video frequency buffer amplifier, although a component is added, the volume and the cost are reduced due to the reduced capacity of an output capacitance. The programmable gain circuit has the advantages of simple structure, small volume and cheap circuit, and the circuit device can effectively ensure the transmission quality of video frequency, and the gain can be adjusted according to demands.
Description
Technical field
The invention belongs to field of video monitoring composite baseband video signal processing technology field, especially a kind of gain programmable vision buffer amplifier circuit with SAG compensation.
Background technology
The vision signal that occurs with the analog baseband signal form exists many factors that influence signal integrity on many transmission links, for example: impedance does not match that the path is tediously long, harmful distributed constant of printed board, be subjected to unreasonable selection that printed board area or cost etc. influence some component parameters or the like all can destroy the Transfer Quality of vision signal directly or indirectly.The result of signal quality variation is, the bandwidth gain unevenness increases, colour reproduction information is destroyed, the decay of signal/noise ratio variation, signal amplitude increases, introduces easily harmonic distortion component etc., and these all can reduce originally the well reproduction quality of vision signal significantly.
In order to improve the quality of vision signal, generally adopt the vision buffer amplifier circuit device of connecting in transmission line that signal is handled, this routine vision buffer amplifier circuit has comprised input AC coupling circuit, operational amplifier and output AC coupling circuit.The ac-coupled circuit of input and output electric capacity has been eliminated the direct voltage on the transmission line, and the earth point that will transmit and receive system is isolated.For the infringement with signal quality is reduced to minimum, the output capacitance capacity must be at the order of magnitude of hundreds of microfarads in this circuit arrangement, and general capacity is greater than 470 μ F, and what often use in broadcasting equipment is the big capacity coupling capacitance of 1000 μ F.100 μ F are the balance points between a physical size and the cost for electric capacity, and behind this capacity, the increase that the volume of electric capacity and cost are rapid not only makes the circuit volume increase, and the cost of the equipment that strengthens.
Summary of the invention
The objective of the invention is to overcome the deficiency of above-mentioned prior art, provide a kind of simple in structure, volume is little, with low cost, effectively guarantee the gain programmable vision buffer amplifier circuit that video transmission quality and gain can be adjusted as required with SAG compensation.
The technical scheme that the present invention takes is:
A kind of gain programmable vision buffer amplifier circuit with SAG compensation, comprise ac-coupled circuit, output resistance R6 and operational amplifier U1, ac-coupled circuit is by R1, R2, R3 and capacitor C 1 constitute the also in-phase input end of concatenation operation amplifier U1, operational amplifier U1 is the input impedance height, the broadband operational amplifier that input bias current is low and support Rail to Rail exports, on the positive pole of operational amplifier U1, also can connect one by inductance L 1 and capacitor C 2, the uncoupling circuit that C3 forms, the output of output resistance R6 connects bnc interface, it is characterized in that: operational amplifier U1 connects one and has the gain programmable circuit that SAG compensates, this programmable circuit is by capacitor C 4, C5, resistance R 4, R5, R8 and gain programmable circuit equivalent resistance R 7 constitute, wherein the output of operational amplifier U1 connects an end of resistance R 4 and capacitor C 4, the inverting input of the other end concatenation operation amplifier U1 of resistance R 4 and an end of capacitor C 5, the other end of capacitor C 4 connects the input of resistance R 5 and output resistance R6, the other end of resistance R 5 connects the other end of capacitor C 5 and an end of resistance R 8, the other end of resistance R 8 connects an end of gain programmable circuit equivalent resistance R 7, the other end ground connection of gain programmable circuit equivalent resistance R 7, gain programmable circuit equivalent resistance R 7 is an adjustable resistance, capacitor C 4 and capacitor C 5 are electrochemical capacitor or ceramic condenser, and its capacity value is 10-47 μ F.
Advantage of the present invention and good effect are:
1. in this amplifier circuit, the capacity controllable of its output capacitance C4 has reduced the volume of integrated circuit thus effectively below 50 μ F, reduced the cost of circuit; And this output capacitance is comprised in the feedback loop of operational amplifier, and constitute the SAG compensating circuits with resistance R 4, resistance R 5 and capacitor C 5, guaranteed that the gain unevenness of vision buffer amplifier circuit in the whole video frequency band is controlled in the minimum scope, obtains good bandwidth response simultaneously.
2. the gain programmable circuit in this amplifier circuit both was made up of adjustable resistance, also can adopt the resistor network by programmable switch control, the sliding end that only need adjust adjustable resistance during use is with resistance that changes adjustable resistance or the purpose that switch is cut or excision resistance is adjusted voltage to reach, changed gain of opening closed controlling resistance network.The adjustment of this resistance can be carried out according to the needs of circuit gain, and not only mode is flexible, and has enlarged the scope of application of this circuit.
3. a small amount of components and parts have been increased though this amplifier circuit is compared with conventional vision buffer amplifier circuit, but because output capacitance reduces the reduction that causes its volume and cost because of capacity, its integrated circuit still has advantage simple in structure, that volume is little, with low cost, and this circuit arrangement can guarantee video transmission quality effectively, and gain can be adjusted as required.
Description of drawings
Fig. 1 is a block diagram of the present invention;
Fig. 2 is circuit theory diagrams of the present invention.
Embodiment
Below in conjunction with embodiment, the present invention is further described, and following embodiment is illustrative, is not determinate, can not limit protection scope of the present invention with following embodiment.
Originally the gain programmable vision buffer amplifier circuit that has the SAG compensation comprises ac-coupled circuit, the uncoupling circuit, operational amplifier U1, SAG (sinking) compensating gain programmable circuit and output circuit, wherein ac-coupled circuit is by R1, R2, R3 and capacitor C 1 constitute the also in-phase input end of concatenation operation amplifier U1, the uncoupling circuit is by inductance L 1 and capacitor C 2, the C3 composition also is connected the operational amplifier positive pole, the output of operational amplifier U1 connects bnc interface by output resistance R6, and what operational amplifier U1 adopted among the present invention is the input impedance height, the broadband operational amplifier that input bias current is low and support Rail to Rail exports.The concrete annexation of foregoing circuit of the present invention is: CVBS (Composite VideoBroadcast Signal) signal input part connects an end of resistance R 1 and capacitor C 1, the other end ground connection of resistance R 1, the other end of capacitor C 1 connects resistance R 2, one end of resistance R 3 and the in-phase input end of operational amplifier U1, the other end of resistance R 2 connects inductance L 1, capacitor C 2, the positive pole of capacitor C 3 one ends and operational amplifier U1, the other end of inductance L 1 connects power supply Vdd, the other end of capacitor C 2 and ground connection after the other end of capacitor C 3 is in parallel, the other end ground connection of resistance R 3, the minus earth of operational amplifier U1.
Innovative point of the present invention is:
Operational amplifier U1 connection one has the gain programmable circuit of feedback and SAG compensation, this programmable circuit is by capacitor C 4, C5, resistance R 4, R5, R8 and equivalent resistance R7 constitute, wherein the output of operational amplifier U1 connects an end of resistance R 4 and capacitor C 4, the inverting input of the other end concatenation operation amplifier U1 of resistance R 4 and an end of capacitor C 5, the other end of capacitor C 4 connects the input of resistance R 5 and output resistance R6, the other end of resistance R 5 connects the other end of capacitor C 5 and an end of resistance R 8, capacitor C 4 and capacitor C 5 are electrochemical capacitor, perhaps also can be ceramic condenser, its capacity value be 10-47 μ F; The other end of resistance R 8 connects an end of gain programmable circuit equivalent resistance R 7, the other end ground connection of gain programmable circuit equivalent resistance R 7.
This gain programmable circuit equivalent resistance R 7 is adjustable resistance (shown in the present embodiment accompanying drawing), or by the resistor network of programmable switch control.
Operation principle of the present invention is:
Input circuit is typical AC coupled mode for signal source (as the video output signals of video camera), is made up of R1, C1, R2, R3.The end of C1 is connected holding of R1 far awayly and is connected with input signal, R1 is the load resistance of input signal source, signal amplitude for 1Vp-p, 75 Ω, the amplitude that 1Vp-p can be arranged on it, the other end of C1 is connected with the series connection node of R2, R3, the series network that R2 and R3 form is connected across between VDD (, L1 can be considered as short circuit) and the ground voltage (U at its series connection node place here
23) be the partial pressure value (U of R2, R3
23=(VDD/ (R2+R3)) * R3).If R2=R3, then U
23Be VDD/2; The input signal and the U that come by C1 coupling
23Behind the superposition, the 0V of signal (OIRE) line is lifted to VDD, as the in-phase input signals for 1 of operational amplifier U1, has satisfied the requirement of the amplifying circuit of single power supply.In view of the characteristics of vision signal, can also make U
23=0.6V (80IRE).
The SAG compensation circuit is made up of R4, C4, R5, C5 and R7 (gain programmable loop equivalent resistance), and feedback loop arises from the output of U1, the inverting input of U1 finally, and feedback quantity depends on the A point current potential in the accompanying drawing.Different with traditional feedback amplifier is, output capacitance C4 is comprised in the feedback loop, it and R4, R5, C5 have constituted an effective SAG compensating circuit again, have guaranteed that the gain unevenness of the buffer amplifier that this patent proposed in the whole video frequency band is controlled in the very low range.Moreover, because output capacitance has also participated in feedback, make this electric capacity that very little number range can be arranged, for example, the output capacitance of tradition similar circuit is when 470uF is above, all be difficult to guarantee the smooth of gain bandwidth, and here the value of output capacitance at 10uF to the bandwidth response that just can obtain between the 30uF quite to be satisfied with.
This gain programmable loop simply to being become by an adjustable resistor group, also can be made up of one group of resistor network and programmable switch.Programmable switch can be selected resistance parameter in the gain ranging of allowing, thereby reaches the purpose of gain variable amplifier, and the design of this variable gain is very significant in video signal transmission system.Because the bandwidth response of this circuit is very smooth, so its gain is only relevant with R4, R5, R8 and R7 (gain programmable loop equivalent resistance):
Gain＝(R4//R5)/(R8+R7)
R4, R5 and R8 are definite value, and after R7 was programmed, the gain of circuit was a determined value.
In fact output loop is made up of an output impedance build-out resistor R6, and when the output impedance that requires circuit was 75 Ω, the R6 value was 75 Ω or slightly little.When output loop was connected with the load of coupling, the overall gain of this amplifier was
Gain′＝Gain?/2
The selection of some component parameters in this circuit:
U1-selects the input impedance height, input bias current is low and support the broadband operational amplifier that Rail to Rail exports, single power supply.
C1-0.22uF is between 1uF, first-selected ceramic dielectric capacitor.
C4, C5-C4=C5,10uF be between 47uF, first-selected ceramic dielectric capacitor.
R1-75 Ω in some applications can be from tens Ω to the OPEN.
R2, R3-except that above statement, can be according to selected U1 at tens K Ω between the hundreds of K Ω.
R4-is between tens K Ω.
R5-1K Ω is between the 10K Ω.
R6-75 Ω or slightly little.
R8-can be 1/3 to 1/2 of R5.
R7-satisfies gain and adjusts the adjustable resistance of requirement or the resistor network of being controlled by programmable switch.
L1, C2, C3-are the uncoupling circuit, can determine voluntarily according to actual conditions.
VDD determines according to desired amplitude output signal, is generally 3V to 5V.
Claims (1)
1. one kind has the gain programmable vision buffer amplifier circuit that SAG compensates, comprise ac-coupled circuit, output resistance R6 and operational amplifier U1, ac-coupled circuit is by R1, R2, R3 and capacitor C 1 constitute the also in-phase input end of concatenation operation amplifier U1, operational amplifier U1 is the input impedance height, the broadband operational amplifier that input bias current is low and support Rail to Rail exports, on the positive pole of operational amplifier U1, also can connect one by inductance L 1 and capacitor C 2, the uncoupling circuit that C3 forms, the output of output resistance R6 connects bnc interface, it is characterized in that: operational amplifier U1 connects one and has the gain programmable circuit that SAG compensates, this programmable circuit is by capacitor C 4, C5, resistance R 4, R5, R8 and gain programmable circuit equivalent resistance R 7 constitute, wherein the output of operational amplifier U1 connects an end of resistance R 4 and capacitor C 4, the inverting input of the other end concatenation operation amplifier U1 of resistance R 4 and an end of capacitor C 5, the other end of capacitor C 4 connects the input of resistance R 5 and output resistance R6, the other end of resistance R 5 connects the other end of capacitor C 5 and an end of resistance R 8, the other end of resistance R 8 connects an end of gain programmable circuit equivalent resistance R 7, the other end ground connection of gain programmable circuit equivalent resistance R 7, gain programmable circuit equivalent resistance R 7 is an adjustable resistance, capacitor C 4 and capacitor C 5 are electrochemical capacitor or ceramic condenser, and its capacity value is 10-47 μ F.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200710057682XA CN101330278B (en) | 2007-06-20 | 2007-06-20 | Gain programmable vision buffer amplifier circuit with SAG compensation |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200710057682XA CN101330278B (en) | 2007-06-20 | 2007-06-20 | Gain programmable vision buffer amplifier circuit with SAG compensation |
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| CN101330278A CN101330278A (en) | 2008-12-24 |
| CN101330278B true CN101330278B (en) | 2011-12-28 |
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| CN200710057682XA Expired - Fee Related CN101330278B (en) | 2007-06-20 | 2007-06-20 | Gain programmable vision buffer amplifier circuit with SAG compensation |
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Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101841675B (en) * | 2010-04-30 | 2011-11-30 | 德讯科技股份有限公司 | Automatic gain compensation system based on analog video wave head detection |
| US10855951B2 (en) * | 2018-07-13 | 2020-12-01 | Analog Devices Global Unlimited Company | Methods and devices for compensating sag effect |
| CN109510953B (en) * | 2018-11-29 | 2021-08-17 | 中国航空工业集团公司沈阳飞机设计研究所 | Conversion circuit for converting S-separation video signal into composite video signal |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5258842A (en) * | 1991-02-14 | 1993-11-02 | Sony Corporation | DC restorer with reduced low frequency noise |
| CN1729504A (en) * | 2002-12-20 | 2006-02-01 | 皇家飞利浦电子股份有限公司 | Video driver with integrated sample-and-hold amplifier and column buffer |
-
2007
- 2007-06-20 CN CN200710057682XA patent/CN101330278B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5258842A (en) * | 1991-02-14 | 1993-11-02 | Sony Corporation | DC restorer with reduced low frequency noise |
| CN1729504A (en) * | 2002-12-20 | 2006-02-01 | 皇家飞利浦电子股份有限公司 | Video driver with integrated sample-and-hold amplifier and column buffer |
Non-Patent Citations (1)
| Title |
|---|
| JP特开2005-184056A 2005.07.07 |
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