CN1286866A - Display driver apparatus - Google Patents
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- CN1286866A CN1286866A CN 97182519 CN97182519A CN1286866A CN 1286866 A CN1286866 A CN 1286866A CN 97182519 CN97182519 CN 97182519 CN 97182519 A CN97182519 A CN 97182519A CN 1286866 A CN1286866 A CN 1286866A
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Abstract
An emitter follower amplifier is coupled between the output of a high voltage video amplifier and the cathode of a kinescope for reducing the effective capacitance presented to the video amplifier that is attributable to the kinescope cathode, socket, spark gaps, and related stray capacitances. A secondary undesired capacitance loading of the video amplifier is effectively reduced by regulating the collector-emitter voltages of the emitter follower output transistors at substantially constant values thereby improving parameters such as slew rate and bandwidth of the overall video display system. Nonlinear circuitry in the follower circuit facilitates accurate AKB current sensing and provides simplification of the voltage regulation circuitry. White limiting circuitry is included within the video amplifier for reducing excess peak white drive that results in objectionable smears. Black limiting circuitry within the video amplifier is also provided to prevent the collapse of the collector-emitter voltage of the push-pull follower output transmistor. The heat sink capacitance of the video amplifier output transistor is screened out via bootstrapping.
Description
The present invention relates generally to amplifier, and be particularly related to a kind of device that the vision signal that drives the picture tube negative electrode is amplified.
In adopting directly perceived or the television equipment of projection kinescope as display device, the amplifier that drives the picture tube negative electrode preferably can provide the drive signal of the high voltage with broadband and high conversion rate.Usually, driving voltage is 200 volts of magnitudes or higher, and in some applications, and for example when not only needing traditional TV to watch but also needing data to show, in fact bandwidth is higher than traditional television standard.In requiring the Video Applications that scans with standard TV line frequency, may need wideer frequency band greater than twice.
For the ease of operation with high pressure, adopt a kind of cascode input stage to drive the cascode amplifier configuration of cobasis output stage usually.This configuration only needs a high voltage transistor (output stage), and because its form connection with common-base configuration, so Miller effect is suppressed and therefore the frequency band operation of non-constant width becomes possibility.In fact, actual bandwidth in cascode amplifier and switching rate are determined according to pay(useful) load electric capacity of presenting to output stage and obtainable output current to a great extent.
Usually, we can make the bandwidth of amplifier and switching rate reach maximum by operating current or the reduction pay(useful) load electric capacity that increases amplifier.But, owing to increase the power dissipation that electric current will inevitably increase amplifier, so preferably adopt the mode that reduces pay(useful) load electric capacity but not improve operating power to improve performance.
In the application of picture tube driver, " effectively " load capacitance of presenting to amplifier mainly be the picture tube negative electrode pay(useful) load electric capacity and with relevant stray capacitances such as base, discharger, electric wire connecting junction.A kind of effective ways that reduce the effective capacitance load are to penetrate with amplifier amplifier and negative electrode coupling by recommending complementation.This amplifier effectively " isolation " approximately with the proportional load capacitance of inverse (" β ") of transistor current gain.The quick charge and the discharge of the extra current proof load electric capacity that provides by this follow-up amplifier, and therefore increase switching rate and bandwidth.For fear of in fact increasing static power dissipation,, wherein apply bias voltage and conduct electricity simultaneously avoiding to push pull transistor normally with " Class B " pattern operation follow-up amplifier.
Penetrate with amplifier the coupling of the load of cascode amplifier and picture tube negative electrode with the example of the picture tube driving amplifier that is used to reduce load capacitance the US patent 4 that is entitled as " video display drive apparatus " through recommending complementation at the John H.Furrey of issue on August 22nd, 1989, be described in 860,107.Be valuably, in the Furrey device, use the complementary pay(useful) load electric capacity (load of picture tube and stray capacitance) that reduces demonstration with driver significantly of penetrating, thereby improve the transient response of positive polarity and negative video signal.
In the United States Patent (USP) that is entitled as " kinescope driver apparatus " 5,680,173 of on October 21st, 19977 issue, people such as white have realized that having complementation and penetrate in the picture tube driving amplifier with output coupling level and can carry out effectively further improving.Specifically, in people's such as white device, recommend complementation and penetrate that coupling is to be used to reduce the effective capacitance of presenting to driving amplifier between the output of high drive amplifier and picture tube negative electrode with amplifier, this effective capacitance is attributable to picture tube negative electrode, base, discharger and relevant stray capacitance.Therefore by the collector electrode-emitter voltage of respectively recommending the follower output transistor being adjusted into constant separately value and improving such as the total switching rate of video display system and the parameter of bandwidth, can reduce effectively the secondary capacitance load of not wishing the amplifier that obtains of the collector-base capacitor that is attributable to follow-up amplifier.
In the above in the prior art of being discussed, by using emitter follower load isolation (Furrey) can realize the reduction of desirable load capacitance, and can further reduce load capacitance by collector electrode-emitter voltage that transistor people such as () White is followed in adjustment.
Can recognize thus and need be further improved to be used for using the picture tube driving amplifier that reduces emitter follower electric capacity adopting positive feedback in the accurate detection that also is desirable to provide the picture tube cathode current of controlling such as automatic developing pipe bias voltage (following is " AKB ").First scheme of the present invention has satisfied this needs.
The kinescope driver apparatus that the present invention relates to comprises that a complementation penetrates with amplifier, this amplifier have one with video amplifier coupling with the input that is used for receiving video signals and have one with the cathode coupled output of picture tube.Feedback circuit is used for each positive feedback voltage is applied to each collector electrode of first and second output transistors of this complementation emitter follower, being used to the making collector electrode-emitter voltage of output transistor keep constant basically, and the AKB current detector is connected in the collector circuit of second output transistor to be used to detect the cathode current of picture tube.
According to the present invention, the output of complementary emitter follower is coupled through the emitter-base bandgap grading of the threshold value actuating switch device and first output transistor, and is coupled through the emitter-base bandgap grading of the resistance device and second output transistor.
According to another feature of the present invention, this feedback circuit has an input that is connected with the node of the threshold value actuating switch device and the first output transistor emitter-base bandgap grading.
According to another feature of the present invention, capacitor and threshold value actuating switch device are connected in parallel between the output of the emitter-base bandgap grading of first output transistor and complementary emitter follower.
Accompanying drawing is represented aforementioned and other feature of the present invention, and wherein components identical is represented with identical reference number, and wherein:
Part shown in Figure 1 is the kinescope driver apparatus that the schematic diagram of block diagram form is represented complementary emitter follower cathode isolation of having of prior art and AKB current detecting;
Part shown in Figure 2 is another embodiment of the schematic diagram of the block diagram form kinescope driver apparatus of representing prior art;
Part shown in Figure 3 is that the schematic diagram of block diagram form represents to embody kinescope driver apparatus of the present invention; And
Part shown in the Figure 4 and 5 is that the schematic diagram of block diagram form is represented another feature of the present invention that load capacitance is reduced in conjunction with device shown in Figure 3.
At first be considered as people's such as White above-mentioned United States Patent (USP) 5,680, Fig. 1 of the embodiment of the kinescope driver apparatus in 173, and consider to use traditional recommending to penetrate with buffer amplifier will to help to understand the present invention to the problem that the output of picture tube cathode capacitance and picture tube driving amplifier isolation is brought.Just as explained above, penetrate with amplifier reduced effectively present to high pressure video drive amplifier be attributable to the negative electrode electric capacity of (with relevant stray capacitance).But follow-up amplifier itself may produce the capacitive load effect to driving amplifier, and tends to limit the performance of total system.
People such as White point out, recommend in the picture tube drive system of emitter follower in use, do not wish that the main root of the capacitive load effect that obtains is attributable to the collector-base capacitor of follower output transistor.Usually, compare with coupled system directly perceived, these electric capacity are less than the picture tube cathode capacitance, and isolate negative electrode with amplifier and can reduce whole electric capacity and improve switching rate and bandwidth by penetrating.But,, preferably can reduce the effective capacitance of penetrating with amplifier itself in order to maximally utilise the buffer action of emitter follower.
For the follower electric capacity in people's such as effective reduction White the device, the occupation mode of feedback is to carry out with the electric current of following in the transistorized collector-base capacitor that reduces under the Dynamic Signal condition.This can realize to keep following between transistorized collector-base the voltage substantially constant by using feedback.So just kept constant collector to-boase voltage.Therefore, under the situation of Dynamic Signal, collector-base capacitor seldom carries out or does not carry out charge or discharge when signal voltage changes.
The effective reduction that is attributable to the follower input capacitance of transistor collector-base capacity is the function that is used to adjust the feedback rates of voltage between collector electrode-emitter-base bandgap grading.For example, if selected feedback rates makes that change in voltage reduces by 50 percent between collector electrode-emitter-base bandgap grading, the reactive current of then collector-base capacitor of follow-up amplifier being charged and discharging also reduces by 50 percent, and " effectively " capacitive load will reduce by half.Along with feedback rates is increased near one, the electric capacity of follower can be reduced more.The measure of taking for the stability of circuit is to guarantee that feedback oscillator is not equal to or surpass one.This is to realize by all " active " semiconductor device in the feedback path that connects voltage or " emitter-base bandgap grading " follower configuration.
Here, Fig. 1 shows an embodiment of people's such as White device, and it comprises that the cathode current of AKB control detects, and describes to carry out improved basis as the present invention at this.Figure 1 shows that a kind of television display system, comprise vision signal is provided to picture tube negative electrode 16 to be used for video signal displayed source 10.In order to simplify the details that this figure does not illustrate picture tube and signal source.Be understandable that for a color system, should have three driving amplifiers.
In short, system comprises the high-voltage amplifier 20 (being shown in dotted line) of a common-emitter common-base class, in order that vision signal is amplified to negative electrode 16 desired high voltage levels.For the electric capacity of the output of high-voltage amplifier 20 and picture tube negative electrode 16 is isolated, the output of amplifier 20 (collector electrode of transistor Q3) is penetrated with amplifier 30 (being shown in dotted line) and negative electrode 16 couplings through recommending complementation.In order to protect driving amplifier to avoid picture tube electric arc, the output 15 of follower is connected with negative electrode 16 with inductance coil l1 by picture tube arc protection resistor R 15.Cathode current testing circuit 40 (" I have been equipped with in order to carry out automatic developing pipe bias voltage (AKB) operation
kDetect ", shown in broken lines), its detects to recommend and penetrates with the collector current of the PNP transistor (Q7) in the amplifier 30 to produce the cathode current I with picture tube negative electrode 16 at output 18
kProportional AKB output signal.This feature be can choose wantonly and can ignore.
At last, in order to reduce the effective capacitance of the collector-base capacitor that is attributable to complementary emitter follower 30 of presenting to high-voltage amplifier, system comprises a feedback control circuit 50 (shown in broken lines), it makes, and voltage keeps substantially constant between the collector electrode-emitter-base bandgap grading of NPN transistor Q4 of follower 30, and this system also comprises another one feedback control circuit 60 (shown in broken lines), and it makes, and voltage keeps substantially constant between the collector electrode-emitter-base bandgap grading of PNP transistor Q7 of follower 30.The transistorized operation of carrying out with voltage between constant set electrode-emitter-base bandgap grading of following makes voltage between collector-base near constant, thereby has reduced the charging and the discharging current amount of following transistorized collector-base capacitor.This result's usefulness is, because driving amplifier 20 needn't provide charging and discharging current to these " parasitism " electric capacity, so improved whole switching rate, bandwidth and transient response characteristic.
The high voltage source (for example 200 volts etc.) that is used for amplifier 20 and feedback or adjusts the operation of circuit 50 and 60 is provided by high pressure (H.V.) power terminal 20.The decoupling of high voltage source terminal 20 is by decoupling network or comprise resistor R 20 and the low pass filter of capacitor C20 provides.Low pressure (L.V.) power terminal 21 provides lower voltage (for example 12 volts etc.), is used for the input of high pressure video drive amplifier 20 and common-emitter common-base level bias voltage.This power supply input is also by comprising the RC network decoupling of resistor R 21 and capacitor C20.
The video input signals that will be exaggerated that source 10 provides is applied to the base stage of common-emitter common-base input transistors through the emitter follower input stage, and wherein this emitter follower input stage comprises grounded collector and the base stage PNP transistor Q1 through input resistor R3 and video inputs 12 couplings.The base stage of the emitter-base bandgap grading of transistor Q1 and transistor Q2 is coupled and is coupled through emitter resistance device R4 and low-tension supply 21.Other high-frequency peaking is by comprising that the series resistor device R1 in parallel with input resistor R3 and other peaking network of capacitor C1 provide.
The collector load of cascode amplifier 20 is provided by the resistor R B that high voltage source 10 is coupled to the collector electrode of common-emitter common-base output transistor Q3.Diode CR2 is built between the collector electrode of loading resistor R8 and transistor Q3 to be provided for reducing complementation and penetrates little bias voltage with the cross (talk) distortion of amplifier 30.
At cascode amplifier 20 duration of works, open-loop gain is directly proportional with the value of loading resistor R8 and the emitter-base bandgap grading network R6, the C2 that discuss with the front and the impedance of R7 are inversely proportional to.Open-loop gain, bandwidth and switching rate also are the functions of the capacitive load (promptly presenting to the electric capacity of the collector electrode of transistor Q3) of the output of amplifier 20.Can reduce this electric capacity by the push-pull transistor of penetrating with amplifier 30 with voltage-operated complementation between constant collector electrode-emitter-base bandgap grading.Suppose that open-loop gain is fully, then closed loop gain is directly proportional with the value of feedback resistor R2 and is inversely proportional to the impedance of fan-in network R1, R3 and C1.
Recommending complementation penetrates with amplifier 30 and comprises a pair of complementary transistor Q4 and the Q7 that output (collector electrode of the Q3) coupling of base stage and amplifier 20 and emitter-base bandgap grading are coupled through separately emitter resistance device R9 and R12 and output 15.Just as noted earlier, penetrating output 15 with the amplifier 30 induction coil L1 and the picture tube electric arc of resistor R 15 through comprising series connection suppresses network and is coupled with negative electrode 16.The supply voltage (collector electrode electromotive force) of following transistor Q4 and Q7 is provided by feedback circuit 50 and 60 separately.
I
kDetecting amplifier 40 is in the feature that embodies automatic developing pipe bias voltage (AKB) circuit and therefore need detect picture tube cathode current " I
k" video display system in use.Detecting amplifier 40 comprises that the cathode current of the collector coupled of an emitter-base bandgap grading and voltage regulating transistor Q9 detects transistor Q10.The reference potential of transistor Q10 base stage is provided by Zener diode CR1.The capacitor C5 in parallel with diode CR1 filters the Zener voltage of being adjusted.With cathode current I
kCollector electrode and loading resistor R16 ground between and at output 18 produce of proportional output voltage by being coupled in transistor Q10.In the application that does not need the AKB operation, can save this detecting amplifier.If saved this detecting amplifier, then the grounded collector of voltage regulating transistor Q9 or with the coupling of another suitable low pressure reference potential.
In order to summarize above-mentioned operation, cascode amplifier 20 amplifies the vision signal that source 10 provides as mentioned above.In order to minimize the capacitive load on the loading resistor R8 that is attributable to the electric capacity relevant with the discharger (not shown) with its base with picture tube 16 and other stray capacitance, the output of cascode-copolar amplifier 20 (collector electrode of transistor Q3) is penetrated with amplifier 30 and the coupling of picture tube negative electrode through recommending complementation.This specific follow-up amplifier is " walking abreast " formula, wherein each base stage parallel connection with the vision signal that is used to receive amplification and each emitter-base bandgap grading parallel connection to be used to drive negative electrode.
Penetrate the device that is comprised with amplifier 30 cathode capacitance of presenting to amplifier 20 is reduced, but also can produce the secondary capacitance effect.In other words be exactly the collector-base capacitor of following transistor Q4 and Q7.Do not wish the capacitance that obtains can reduce the idle charging and the discharging current that offer these electric capacity in order to reduce these effectively.This feature is provided by two positive feedback adjusters 50 and 60, and voltage remains constant between transistorized collector electrode-emitter-base bandgap grading following for they.
For example, if the output voltage of amplifier 20 raises, the emitter voltage of then following transistor Q4 also will raise, but Zener diode CR3 and voltage regulating transistor Q6 follow increase the collector voltage of transistor Q4.Similarly, if the output voltage of step-down amplifier 20, the emitter voltage of then following transistor Q4 also will reduce, and Zener diode CR3 and the voltage regulating transistor Q6 collector voltage of reduction being followed transistor Q4.As shown in the figure, if Zener voltage is 10 volts, then voltage equals Zener voltage between collector electrode-emitter-base bandgap grading of transistor Q4.If the supposition Zener voltage is 10 volts, voltage will be about 10 volts between collector electrode-emitter-base bandgap grading of the transistor Q4 that is then produced.
Therefore, no matter the follower input voltage increases is still reduced, and it is constant that the voltage at the collector electrode of this follower-emitter-base bandgap grading two ends keeps.Because input signal is through flex point, so the emitter of base voltage when following transistor biasing conducting or bias-off (recommending operation) will change the hundreds of millivolt.But the variation of voltage is compared small with collector electrode-emitter voltage of being adjusted (for example Zener voltage of 10 volts etc.) between base stage-emitter-base bandgap grading as can be seen.Therefore, we can think that the variation " substantially " of voltage is constant between collector-base, and the charging and the discharge of collector-base capacitor are seldom arranged under the Dynamic Signal condition basically.Because this reactive current is suppressed, so the effective collector-base capacity of follow-up amplifier is lowered.
As mentioned above, be used to adjust the feedback of following voltage between transistorized collector electrode-emitter-base bandgap grading near absolutely but can not equal one, this is because if then need unlimited transistor Q5 and the current gain of Q6 at that rate.In other words, transistor Q5 all is connected as emitter follower with Q6, and the gain near but less than one.Correspondingly, even just be fed back to, this circuit also is stable.In a given application, can use still less feedback quantity if necessary such as 50%.It should be noted that actual Zener voltage is not the key parameter of this circuit.The Zener by-pass capacitor (C3 or C4) provide desirable voltage regulator AC the reduction of impedance, and then be convenient to broadband operation.
Fig. 2 shows second embodiment by the disclosed picture tube driver of people such as White.In this embodiment, as shown in the figure, be connected with follow-up amplifier 30A with 60B with R13 and feedback control circuit 50B and can reduce total component count by removing transistor Q5 and Q6 and resistor R 10.But, this embodiment also not exclusively is fit to detect use with above-mentioned AKB, this is because the AKB testing circuit added to can make undesirable electric current at AKB interim this AKB testing circuit of flowing through among second embodiment, thereby influences the accuracy that AKB controls unfriendly.This influence in other situation will be described in following the present invention.
Figure 3 shows that according to the present invention people's such as above-mentioned White the improvement that device carried out.Picture tube driver of the present invention uses emitter follower the positive feedback and the AKB current detecting of the video amplifier and picture tube coupling and this emitter follower electric capacity of use reduction.Need six active elements (Q4-Q9) although the output stage of White device is penetrated with amplifier, the present invention only needs four active elements (Q4, Q6, Q7 and Q9).Other improvement according to the present invention comprises improved AKB detecting operation, the AC of improved output stage operation, and difference is with reference to the interpolation of input stage, the interpolation of the white and black restricting circuits in the video amplifier level, and fin electric capacity is booted.
As shown in Figure 3, AKB testing circuit of the present invention comprises that one is penetrated with transistor, and its base input end is connected with low-tension supply end 21, and its collector electrode is connected with potential-divider network (R16A and R16B) and its emitter-base bandgap grading is connected with the collector electrode of transistor Q9.Capacitor C5 is parallel to the node two ends of base stage/emitter-base bandgap grading of Q10, to be used to provide cushioning effect.
For carrying out improved AKB detecting operation greater than the DC output voltage about VCC2 (R14/ (R14+R11)).The net current that arrives threshold value conducting device (Zener diode) CR3 and CR4 is for just and by transistor Q4 and Q6 providing.Equal the situation of resistor R 11 for resistor R 14, the positive net current that arrives diode CR3 and CR4 takes place greater than a half of the voltage (for example VCC2) of the high voltage source of terminal 20 approximately at the DC output voltage.So then provide AKB more than sufficient to detect by the scope of measuring.For the situation of DC, the output bias diode network of CR2A and CR2B makes the voltage at diode CR2C two ends be about zero, so not conducting of CR2C.In these cases, because diode CR2C bias-off, the emitter of transistor Q7 so the DC cathode current must be flowed through, thereby, the collector current of transistor Q9 represents that the error that is had equals the sum reciprocal of the β of transistor Q7 and Q9 through the CRT cathode current of sensor coil L1 and resistor R 16.
The cushioning effect that AKB detects transistor Q10 and capacitor C5 provides DC and AC Low ESR at the collector electrode of transistor Q9, and provides and the proportional " I of CRT cathode current
kDetect " necessity restriction of voltage.The DC of transistor Q9 collector electrode and AC Low ESR are to keep the frequency response of CRT driver-level needed.Because peak cathode current can reach dozens of mA, simultaneously the AKB cut-off current is dozens of uA, so we are needed just for this restriction.For the high cathode electric current, saturated and its collector voltage of transistor Q10 is restricted to VCC1+Vbe (base stage/emitter voltage of transistor Q10).The further damping peak I of resistance pressure-dividing network R16A and R16B
kDetect voltage.When ending, transistor Q10 operates and I in its range of linearity as common base stage
kVoltage be substantially equal to the CRT cathode current and multiply by resistor R 16B (be assumed to high impedance detect).
The AC operation of bootstrapping output stage is identical with the operation in people's such as White the device basically.That is to say, by arriving the F that frequency is far smaller than Q4 and Q7
TDescribed device collector electrode can eliminate the collector-base input capacitance C of transistor Q4 and Q7 near one positive voltage feedback
CbUseful is, can realize feedback near one by using in each feedback circuit than the desired active element (transistor) that lacks of people such as White.And capacitor C200 provides at the two ends of threshold value conducting device (diode) CR2C, with the coring (coring) of the small-signal AC that is used to reduce the signal that drives the CRT negative electrode.
With reference to input circuit (206) with penetrate increase with transistor (Q1B) level and make the collector current of transistor Q2 and Q3 of flowing through be directly proportional with voltage difference between " video IN " and " Ref IN " input (being respectively terminal 12A and 12B), thereby at the small-signal of TV or demonstration partly and good ground connection difference inhibition is provided between the large-signal CRT driver-level.(just because of this, video signal source 10 provides vision signal S1 to input 12A, and vision signal reference voltage S2 is provided the input 12B to cascode amplifier 20.) lack sufficient ground signalling and suppress to cause " playback ", beat and extra noise and artificial disturbance (artifact pickup).Be lowered by making " video IN " (12A) be high impedance, penetrating from the signal width of cloth of signal or earth current with " Ref IN " input (12B).
White restricting circuits 200 (shown in broken lines) comprises transistor Q1, diode D1 and resistor R 20 and R21.This meets the requirements, and may make instantaneous overdriving become harmful stain because drive transistor Q3, the Q4 or the saturated of Q7 that cause by the mistake peak white.The effect of transistor Q1 and resistor R 20 and R21 is enough to provide restriction, can steadily and produce the restriction of pleasant more but add diode D1.In addition, diode D1 produces the temperature-compensating of difference input (Ref IN) 12B that is about net value zero Vbe.
Be understandable that, shown in one side of resistor R 12 ground connection can be connected with the emitter-base bandgap grading of reference input transistors Q2 and ground connection no longer.This must will provide identical restriction, but institute's reference is " Ref IN " signal but not ground.
Voltage Vce weakens between collector electrode-emitter-base bandgap grading that " infrablack " peak value can make transistor Q3 although the seriousness of consequence less than crossing white peak, is crossed, and makes these excessive black transient states become bigger, and is more visible.Can eliminate this situation by between the emitter-base bandgap grading of transistor Q3 and ground, adding resistor R 202.Be selected to prevent that from the flow through DC electric current of resistor R 202 of grounded-base transistor Q3 the voltage of transistor Q4 from weakening, even when not having electric current to flow through the emitter of transistor Q4.
The restriction switching rate of the frequency response of CRT driver and it is at first definite by the value of the clean electric capacity (Cc) of the collector electrode of transistor Q3 (output of the video amplifier) and resistor R 8.Selected capacitor C 2 so that (R8) product of (Cc) equal (R7) product (C2).This is used to compensate roll-off (the roll off) of the small-signal that clean capacitor C c and resistor R 8 by transistor Q3 cause.But between big blackening transient period, this compensation is inoperative, and this is because the collector current of transistor Q3 and Q2 can not become negative.
Preferably can reduce the effective value of Cc as much as possible, the peak signal response of resistor R 8 of set-point of the power dissipation of transistor Q3 is set with generation.The source of the clean capacitor C c of transistor Q3 comprises the input capacitance of transistor Q4 and Q7, the collector-base capacitor Ccb of transistor Q3, the fin electric capacity of wiring capacitance and transistor Q3.
Operate as emitter follower by the collector electrode of bootstrap transistor Q4 and Q7 and with them, in fact the input capacitance of transistor Q4 and Q7 is eliminated.
The fin electric capacity of transistor Q3 is presented as from the collector electrode of transistor Q3 to the capacitor as the actual fin of typical metal assembly.By being electrically connected the fin of transistor Q3 or with output 15 or with the signal of the emitter of transistor Q4 or Q7, the electric capacity that is increased by the fin of transistor Q3 can be sized or boot.The emitter voltage of transistor Q4 and Q7 is followed the collector voltage of transistor Q3 and is had one and is slightly less than one postiive gain.
Fig. 4 shows the device that reduces the fin effective capacitance by positive feedback.Herein, the output of the output of transistor Q4 or Q7 emitter or output 15 is provided to the fin 500 of transistor Q3 by DC or AC coupling.Transistor Q3 and fin 500 thermal couplings.For the DC shielding, the output of transistor Q4 or Q7 or output 15 is applied directly to fin 500 through terminal 502, perhaps carries out the AC coupling through capacitor 506 and AC coupled end 508.Under any one situation therein, advantageously the pay(useful) load electric capacity of driving amplifier 30 reduces only, and therefore bandwidth and switching rate increase.
As shown in Figure 5, fin also can ground connection (advantage is a safety), wherein connect (DC coupled end 602) or arrive the emitter of transistor Q4, emitter or the outlet terminal 15 of transistor Q7 by AC coupling (capacitor 610 and AC coupled end 608) by direct current, positive feedback is applied to screening conductor 606.The method seldom can obtain the high efficiency of heat and electricity, but has some benefit of safety, for example avoids the dangerous electromotive force on the fin.
Feedback voltage and fin or be of value to the potential safety hazard that reduces fin with the example of the AC of screen coupling are coupled the same effective with DC through terminal 502 or 602 simultaneously.
Claims (10)
1. display driver comprises:
Be configured in the first transistor in first drive circuit, be used for first first drive signal that detects being offered first output by the response video input signals;
Be configured in the transistor seconds in second drive circuit, be used for second second drive signal that detects is offered second output;
A feedback circuit, the described input of described display unit and at least the response video input signals described first drive circuit between be coupled;
Testing circuit with the coupling of described second circuit is used for detecting in second interim parameter of described display unit; And
A circuit, be used for first and second outputs separately of described first and second drive circuits and the input coupling of described display unit in first interim, and be used for described feedback circuit and the described second drive circuit decoupling in described second interim.
2. display driver according to claim 1, wherein said first and second drivers dispose with the form of recommending configuration according to the described input of described display unit.
3. display driver according to claim 1, wherein said the first transistor are first kind of conduction types,
Described transistor seconds is the described transistor seconds of the second kind conduction type opposite with described the first transistor, and
Described first and second transistors are with the form configuration of complementary push-pull configuration, and wherein the described input of each output electrode and described display unit is coupled.
4. display driver according to claim 3, wherein said coupling and uncoupling circuit are connected between the described first and second transistorized described output electrodes.
5. display driver according to claim 4, wherein said first and second transistors are bipolar transistors, and described output electrode is an emitter.
6. display driver according to claim 5, wherein said decoupling circuit comprise a threshold value conducting device.
7. display driver according to claim 6, wherein said threshold value conducting device are diodes.
8. display driver according to claim 3, wherein said decoupling circuit comprise a threshold value conducting device.
9. display driver according to claim 8, wherein said threshold value conducting device are diodes.
10. display driver according to claim 1, wherein said first is the sweep spacing corresponding to the active part of described video input signals at interval,
Described second is the blanking interval corresponding to the invalid part of described video input signals at interval, and
Testing circuit and the coupling of described second drive circuit are to be used for detecting the described parameter of described demonstration during described blanking interval.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB97182519XA CN1182701C (en) | 1997-12-12 | 1997-12-12 | Display driver apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB97182519XA CN1182701C (en) | 1997-12-12 | 1997-12-12 | Display driver apparatus |
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| Publication Number | Publication Date |
|---|---|
| CN1286866A true CN1286866A (en) | 2001-03-07 |
| CN1182701C CN1182701C (en) | 2004-12-29 |
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|---|---|---|---|
| CNB97182519XA Expired - Fee Related CN1182701C (en) | 1997-12-12 | 1997-12-12 | Display driver apparatus |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100433113C (en) * | 2001-03-12 | 2008-11-12 | 汤姆森特许公司 | Reducing sparkle artifacts with post gamma correction slew rate limiting |
| CN102045516A (en) * | 2009-10-16 | 2011-05-04 | 深圳Tcl新技术有限公司 | Television video output circuit |
| CN104599629A (en) * | 2014-12-16 | 2015-05-06 | 上海天马有机发光显示技术有限公司 | Driving circuit, lighting control circuit, display panel and display device |
-
1997
- 1997-12-12 CN CNB97182519XA patent/CN1182701C/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100433113C (en) * | 2001-03-12 | 2008-11-12 | 汤姆森特许公司 | Reducing sparkle artifacts with post gamma correction slew rate limiting |
| CN102045516A (en) * | 2009-10-16 | 2011-05-04 | 深圳Tcl新技术有限公司 | Television video output circuit |
| CN102045516B (en) * | 2009-10-16 | 2013-06-26 | 深圳Tcl新技术有限公司 | Television video output circuit |
| CN104599629A (en) * | 2014-12-16 | 2015-05-06 | 上海天马有机发光显示技术有限公司 | Driving circuit, lighting control circuit, display panel and display device |
Also Published As
| Publication number | Publication date |
|---|---|
| CN1182701C (en) | 2004-12-29 |
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Granted publication date: 20041229 Termination date: 20100112 |