LM1279A 110 MHz RGB Video Amplifier System with OSD General Description The LM1279A is a full featured and low cost video amplifier with OSD (On Screen Display). 8V operation for low power and increased reliability. Supplied in a 20-pin DIP package, accommodating very compact designs of the video channel requiring OSD. All video functions controlled by 0V to 4V high impedance DC inputs. This provides easy interfacing to 5V DACs used in computer controlled systems and digital alignment systems. Unique OSD switching, no OSD switching signal required. An OSD signal at any OSD input typically switches the LM1279A to the OSD mode within 5 ns. Ideal video amplifier for the low cost OSD monitor with resolutions up to 1024 x 768. The LM1279A provides superior protection against ESD. Excellent alternative for the MC13282 in new designs. Features n Three wideband video amplifiers 110 MHz @ −3dB (4 VPP output) n OSD signal to any OSD input pin automatically switches all 3 outputs to the OSD mode Fast OSD switching time, typically 5 ns 3.5 kV ESD protection Fixed cutoff level typically set to 1.2V 0V to 4V, high impedance DC contrast control with over 40 dB range n 0V to 4V, high impedance DC drive control (0 dB to −12 dB range) n Matched ( ± 0.1 dB or 1.2%) attenuators for contrast control n Output stage directly drives most hybrid or discrete CRT drivers n n n n Applications n n n n High resolution RGB CRT monitors Video AGC amplifiers Wideband amplifiers with contrast and drive controls Interface amplifiers for LCD or CCD systems Block and Connection Diagram DS101250-1 FIGURE 1. Order Number LM1279AN See NS Package Number N20A © 1999 National Semiconductor Corporation DS101250 www.national.com LM1279A 110 MHz RGB Video Amplifier System with OSD October 1999 LM1279A Absolute Maximum Ratings (Note 1) Thermal Resistance to Case (θJA) Junction Temperature (TJ) ESD Susceptibility (Note 4) ESD Machine Model (Note 16) Storage Temperature Lead Temperature (Soldering, 10 sec.) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Pins 2 and 16 (Note 3) Peak Video Output Source Current (Any One Amp) Pins 13, 15, or 18 Voltage at Any Input Pin (VIN) Power Dissipation (PD) (Above 25˚C Derate Based on θJA and TJ) Thermal Resistance to Ambient (θJA) 10V VCC ≥ VIN 28 mA ≥ GND 37˚C/W 150˚C 3.5 kV 300V −65˚C to 150˚C 265˚C Operating Ratings (Note 2) Temperature Range Supply Voltage (VCC) 0˚C to 70˚C 7.5V ≤ VCC ≤ 8.5V 2.1W 60˚C/W DC Electrical Characteristics TA = 25˚C; VCC1 = VCC2 = 8V; V10 = 4V; VDrive = 4V; V11 = 7V; VOSD = 0V unless otherwise stated. Symbol Parameter Condition IS Supply Current V3, 5, 8 Video Amplifier Input Bias Voltage RIN Video Input Resistance V11clamp Clamp Voltage I11 clamp off Clamp Off Current V11 = 0V I11 clamp on Clamp On Current V11 = 6.5V I clamp Clamp Cap Charge Current Clamp Comparators On I bias Clamp Cap Bias Discharge Current Clamp Comparators Off ICC1 + ICC2 − ILoad (Note 7) Any One Amplifier Typical (Note 5) Limit (Note 6) Units 80 90 mA(max) 2.5 V 20 kΩ 3.2 3.6 V (min) −5.0 −8.0 µA(max) −100 −500 nA (max) ± 750 ± 500 µA(min) 50 200 nA (max) 1.35 1.55 V (max) ± 50 ± 200 mV (max) 5.0 4.6 V (min) −0.25 −1.5 µA (max) VOL Video Black Level VVideo ∆VOL Video ∆Black Level Output Voltage Between Any Two Amplifiers VOH Video Output High Voltage V11 < 1.2V I10, 12, 14, 17 Contrast/Drive Control Input Current VContrast = VDrive = 0V to 4V I1I, 19I, 20I OSD Low Input Current (each) VOSD in = 0V −2.5 −10 µA(max) I1h, 19h, 20h OSD High Input Current (each) VOSD in = 5V 100 130 µA (max) in = 0V, V11 = 6.5V AC Electical Characteristics TA = 25˚C; VCC1 = VCC2 = 8V. Manually adjust Video Output pins 13, 15, and 18 to 4V DC for the AC test unless otherwise stated. (Note 15) Symbol AVmax Parameter Video Amplifier Gain Conditions Typical (Note 5) Limit (Note 6) Units V10 = 4V, VIN = 635 mVPP 6.8 5.9 V/V (min) Vdrive = 4V 16.7 15.4 dB (min) ∆AV 2V Contrast Attenuation @ 2V Ref: AV max, V10 = 2V −6 dB ∆AV 0.25V Contrast Attenuation @ 0V Ref: AV max, V10 = 0V −35 dB ∆Drive Drive Control Range Vdrive = 0V to 4V, V10 = 4V AV match Absolute Gain Match @ AV max V10 = 4V, Vdrive = 4V (Note 9) AV track Gain Change Between Amplifiers V10 = 4V to 2V (Notes 9, 10) f(−3 dB) Video Amplifier Bandwidth V10 = 4V, Vdrive = 4V, (Notes 11, 12)) VO = 3.5 VP-P 12 dB ± 0.3 ± 0.3 dB 110 MHz ns dB tr(Video) Video Output Rise Time VO = 3.5 VP-P (Note 11) 3.6 tf(Video) Video Output Fall Time VO = 3.5 VP-P (Note 11) 3.2 ns Vsep 10 kHz Video Amplifier 10 kHz Isolation V10 = 4V (Note 13) −70 dB www.national.com 2 (Continued) Symbol Parameter Conditions Typical (Note 5) Limit (Note 6) Vsep 10 MHz Video Amplifier 10 MHz Isolation V10 = 4V (Notes 11, 13) ∆VOL(OSD) OSD Black Level, Difference from Video Black Level VOSD VOH(OSD) OSD Output High Voltage (above measured video black level) VOSD tr(OSD) Going into OSD Mode OSD Mode (Figure 2) 5.0 ns tf(OSD) Going out of OSD Mode OSD Mode (Figure 2) 10.0 ns in = 0.8V, OSD Mode in = 2.5V, OSD Mode −50 Units dB −0.4 −0.7 V (max) 2.1 2.4 V (max) tr-prop(OSD) Starting OSD Propagation Delay Switching to OSD Mode (Figure 3) 13.0 ns tf-prop(OSD) Ending OSD Propagation Delay Switching to Vid. Mode (Figure 3) 14.0 ns Tpw(Clamp) Input Clamp Pulse Width (Note 14) 200 ns (min) Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Note 2: Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 3: VCC supply pins 2 and 16 must be externally wired together to prevent internal damage during VCC power on/off cycles. Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 5: Typical specifications are specified at +25˚C and represent the most likely parametric norm. Note 6: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 7: The supply current specified is the current for VCC1 and VCC2 minus the current through RL (Isupply = ICC1 + ICC2 − IL). The supply current for VCC2 (pin 16) does depend on the output load. With video output at 1V DC, the additional current through VCC2 is 7.7 mA with RL = 390Ω. Note 8: Output voltage is dependent on load resistor. Test circuit uses RL = 390Ω. Note 9: Measure gain difference between any two amplifiers. VIN = 635 mVPP. Note 10: ∆AV track is a measure of the ability of any two amplifiers to track each other and quantifies the matching of the three attenuators. It is the difference in gain change between any two amplifiers with the contrast voltage (V10) at either 4V or 2V measured relative to an AV max condition, V10 = 4V. For example, at AV max the three amplifiers’ gains might be 17.1 dB, 16.9 dB, and 16.8 dB and change to 11.2 dB, 10.9 dB and 10.7 dB respectively for V10 = 2V. This yields the measured typical ± 0.1 dB channel tracking. Note 11: When measuring video amplifier bandwidth or pulse rise and fall times, a double sided full ground plane printed circuit board without socked is recommended. Video amplifier 10 MHz isolation test also requires this printed circuit board. The reason for a double sided full ground plane PCB is that large measurement variations occur in single sided PCBs. Note 12: Adjust input frequency from 10 MHz (AV max reference level) to the −3 dB corner frequency (f−3 dB). Note 13: Measure output levels of the other two undriven amplifiers relative to the driven amplifier to determine channel separation. Terminate the undriven amplifier inputs to simulate generator loading. Repeat test at fIN = 10 MHz for Vsep 10 MHz. Note 14: A minimum pulse width of 200 ns is guaranteed for a horizontal line of 15 kHz. This limit is guaranteed by design. If a lower line rate is used then a longer clamp pulse may be required. Note 15: During the AC test the 4V DC level is the center voltage of the AC output signal. For example, if the output is 4 VPP the signal will swing between 2V DC and 6V DC. Note 16: Machine Model ESD test is covered by specification EIAJ IC-121-1981. A 200 pF cap is charged to the specified voltage, then discharged directly into the IC with no external series resistor (resistance of discharge path must be under 50Ω). 3 www.national.com LM1279A AC Electical Characteristics TA = 25˚C; VCC1 = VCC2 = 8V. Manually adjust Video Output pins 13, 15, and 18 to 4V DC for the AC test unless otherwise stated. (Note 15) LM1279A Timing Diagrams DS101250-2 FIGURE 2. OSD Rise and Fall Times DS101250-3 FIGURE 3. OSD Propagation Delays www.national.com 4 LM1279A Test Circuits DS101250-5 **Note: All video inputs must have a series 30Ω resistor for protection against EOS (Electrical Over Stress). If the OSD signals are external to the monitor, or these signals are present any time when +8V is not fully powered up, then the OSD inputs also require a series 30Ω resistor. FIGURE 4. LM1279A OSD Video Pre-amp Demonstration Board Schematic 5 www.national.com LM1279A Pin Descriptions Pin No. Pin Name Schematic Description These are standard TTL inputs. An OSD signal at any of the three pins will automatically switch the pre-amp into the OSD mode. 7 colors, including white, are available. 1 Red OSD Input 19 Blue OSD Input 20 Green OSD Input 2 VCC1 Power supply pin (excluding output stage) 3 Red Video In 5 Green Video In Video inputs. These inputs must be AC Coupled with a minimum of a 1 µF cap, 10 µF is preferred. A series resistor of about 33Ω must be used for ESD protection. 8 Blue Video In 4 Red Clamp Cap 7 Green Clamp Cap 9 Blue Clamp Cap The external clamp cap is charged and discharged to the correction voltage needed for DC restoration. 0.1 µF is the recommended value. 6 Ground Ground pin. 10 Contrast 12 Blue Drive 14 Green Drive Contrast control pin: 4V - no attenuation 0V - over 40 dB attenuation Drive control pins: 4V - no attenuation 0V - 20 dB attenuation 17 Red Drive 11 Clamp Pulse The clamp pulse activates the DC restoration circuitry. A 3.6V input is required to activate the clamp pulse. 13 Blue Video Out Video output. For proper black level the output must drive 390Ω impedance. 15 Green Video Out 18 Red Video Out www.national.com 6 Pin No. 16 LM1279A Pin Descriptions (Continued) Pin Name Schematic Description Power supply pin for the output stage. There are no internal connections to VCC1. VCC2 ESD and Arc-Over Protection against arc-over. The pre-amp vulnerability is mainly through the ground traces on the PCB. For proper operation all ground connections associated with the video pre-amp, including the grounds to the bypass capacitors, must have short returns to the ground pins. A significant ground plane should be used to connect all the pre-amp grounds. Figure 16, the demo board layout, is an excellent example on an effective ground plane, yet using only a single sided PCB layout. Here is a check list to make sure a PC board layout has good grounding: The ESD cells of the LM1279A are improved over the ESD cells used in typical video pre-amps. The monitor designer must still use good PC board layout techniques when designing with the LM1279A. The human body model ESD susceptibility of these parts is rated at 3 kV (Note 4). However, many monitor manufacturers are now testing their monitors to the level 4 of the IEC 801-2 specification. This requires the inputs to the monitor to survive an 8 kV discharge. If the monitor designer expects to survive such levels he MUST provide external ESD protection to the video pre-amp inputs! PC board layout is very important with LM1279A as with other video pre-amps. The LM1279A provides excellent protection against ESD and arc-over, but the LM1279A is not a substitute for good PCB layout. Figure 5 shows the recommended input protection for a video pre-amp. The two diodes at the video pre-amp input and after the 30Ω series resistor offers the best protection against ESD. When this protection is combined with a good PCB layout, the video pre-amp will easily survive the IEC 801-2 level 4 (8 kV ESD) testing commonly done by monitor manufacturers. If the protection diodes are moved to the video input side of the 30Ω resistor, then the ESD protection will be less effective. There is also the risk of damaging the diodes since there is no resistor for current limiting. In such a design a heavier duty diode, such as the FDH400, should be used. It is strongly recommended that the protection diodes be added as shown in Figure 5. The 1N4148 diode has a maximum capacitance of 4 pF. This would have little affect on the response of the video system due to the low impedance of the input video. Many monitor designers prefer to use a single zener diode instead of the recommended two diodes at the video preamp input. The required location of the zener diode is shown in Figure 5. It is shown as a dashed line, indicating an alternative to the two diode solution. The zener diode does give the savings of one component, but now the protection is less effective. To minimize capacitance, the zener diode needs to have a zener voltage of 24V or higher. This is well above the VCC voltage of the LM1279A. The zener diode must be located at the video input for protection against a low voltage surge. The 30Ω resistor is needed to limit the current of such a voltage surge, protecting the video pre-amp. Protection against ESD by using a zener diode is about as effective as having the two diodes at the video input (same location as the zener diode). A higher series resistor may be necessary for protection against the zener voltage, but the higher resistor value will impair the performance of the LM1279A; resulting in a lower bandwidth and a less stable black level. For maximum reliability the monitor designer should not consider the zener diode solution for ESD protection of the LM1279A. The ESD cells of the LM1279A also gives good tolerance against arc-over. Once again the monitor designer must be careful in his PCB layout for good arc-over protection. In the video chain only the outputs of the CRT driver are directly exposed to the voltages that may occur during arc-over. A good PCB layout is the best protection for the video pre-amp • All associated grounds with the video pre-amp are connected together through a large ground plane. • CRT driver ground is connected to the video pre-amp ground at one point. • CRT and arc protection grounds are connected directly to chassis, or the main ground. There is no arc-over current flow from these grounds through the pre-amp or CRT driver grounds. If any one of the above suggestions are not followed, then the LM1279A may become vulnerable to arc-over. Improper grounding is by far the most common cause of a video preamp failure during arc-over. DS101250-12 FIGURE 5. Recommended Video Input ESD Protection Functional Description Figure 1 on the front page shows the block diagram of the LM1279A along with the pinout of the IC. Each channel receives a video input signal at its input amplifier (-A1). The output of the input amplifier goes to the contrast attenuator stage. For easy interfacing to 5V DACs all controls inputs, including the contrast control, use a 0V to 4V range. The contrast control has no attenuation with an input of 4V, and has full attenuation (over −40 dB) with a 0V input. All three channels will accurately track the contrast control setting at pin 10. Each channel will have the same amount of attenuation for a given input voltage typically to within ± 0.3 dB. All channels will track because the contrast control is the first stage of attenuation and the internal control voltage generated from the input voltage is common to all three channels. The output of the contrast attenuator goes to the drive attenuator. This stage has a 12 dB control range. This stage is used for color balance, so the adjustment range has been limited to 12 dB for a more accurate color balance. Each 7 www.national.com LM1279A Functional Description drivers can be used in this board, but the LM2407 is considered the best match to the LM1279A based on cost and performance. Some important notes on Figure 4. All three video inputs have a 75Ω terminating resistor for a 75Ω video system. This is the normal video impedance of the video from a computer system. It is possible to also have a 50Ω system, then R1, R3, and R5 would be changed to 50Ω. R2, R4, and R6 are in series with the video inputs of the LM1279A. These three 30Ω resistors are required to protect the IC from any sudden voltage surges that may result during the power up and power down modes, or when connecting the monitor to other equipment. The monitor designer must include these resistors in his design for good monitor reliability. If additional protection against ESD at the video inputs is necessary, then adding clamp diodes on the IC side of the 30Ω resistors is recommended, one to VCC1 and one to ground (see Figure 5). Sometimes a designer may want to increase the value of the 30Ω resistors at the video inputs, for additional ESD protection. This is not recommended with the LM1279A. C5, C7, and C9 are part of the DC restoration circuit. This circuit is depending on a total maximum circuit resistance of about 110Ω; 30Ω input series resistor plus 75Ω for the video termination resistor. Increasing the value of the 30Ω resistors will exceed the 110Ω limit. The excellent internal ESD protection and the external clamp diodes (if needed) will provide excellent ESD protection. The 30Ω resistors in series with the OSD inputs are also necessary if the OSD signals are external to the monitor, or if these signals are present any time when the +8V is not fully powered up. Interfacing to the OSD inputs is quite easy since the signal processing necessary to match the OSD signals to the video levels is done internal by the LM1279A. There is also no need for an OSD window signal. Any time there is a high TTL signal at any of the three OSD inputs, the LM1279A will automatically switch to the OSD mode. A high TTL OSD signal will give a high video output for that color. The OSD level is fixed, typically 2.3V above the video black level. This will give a fixed brightness to the OSD window, but not at maximum video brightness which could be unpleasant to the user. Figure 2 and Figure 3 show the timing diagrams of the OSD signals for the LM1279A. The recommended load impedance for the LM1279A is 390Ω. However, some changes in the load impedance can be made. If the load impedance is reduced, the monitor designer must confirm that the part is still operating in its proper die temperature range, never exceeding a die temperature of 150˚C. When changing the load impedance, the black level shift is shown in the chart below. The measured VP-P output with under 1% distortion is also listed. (Continued) channel has its own independent control pin with the 0V to 4V control range. An input of 4V give no attenuation, and an input of 0V gives the full 12 dB attenuation. The output of the drive attenuator stage goes to the inverting input of A2. Since this is the second inversion stage, the output of A2 will be the non-inverted video signal. Note that the output of gm1 goes to the non-inverting input of A2. Also note that the output of A2 goes to the inverting input of gm1. This is the feedback for the clamp circuitry. The output stage of A2 is an exact duplicate of the video output through A3. If a 390Ω load impedance is used at the video output, then the black level at the output stage will accurately track the output of A2. The other input to gm1 is the desired black level output of the LM1279A. Since the LM1279A has a fixed black level output, the non-inverting inputs to gm1 in all three channels go to a fixed 1.35V internal reference. This sets the black level output to a nominal 1.35V. gm1 acts like a sample and hold amplifier. Once the clamp pulse exceeds 3.6V gm1 is activated, driving the input of A2 to a level where the video output will be 1.35V. For proper DC restoration it is important that gm1 be activated only during the horizontal flyback time when the video is at the black level. gm1 also charges the clamp cap to the correct voltage to maintain a 1.35V black level at the video output. When gm1 is turned off the voltage stored on the clamp cap will maintain the correct black level during the active video, thus restoring the DC level for a 1.35V black level. The input of A3 receives the output from A2. The video channel of A3 is a duplication of the output stage to A2. As mentioned in the previous paragraph this is done so that the DC restoration can be done at the A2 stage. A3 also receives the OSD input for blanking the channels with no OSD input. By doing DC restoration at the A2 stage, OSD can be activated at the output stage during the time DC restoration is being done at A2. The OSD signal goes into a special interface circuit. The output of this circuit will drive the output of A3 to either an OSD black level or to about 2.4V above the video black level (OSD white level). The OSD black level is about 300 mV below the video black level. This guarantees that if the OSD signal is not activated for a particular channel, then its output will be slightly below the cutoff level. If an OSD input is received in a particular channel, then the video output will be at the OSD white level. The OSD mode is automatically activated if there is only one OSD signal to any of the video channels. This OSD control circuit will allow any color, except black, during the OSD mode. This also saves the need for a special signal to switch into the OSD mode. Remember that at least one OSD input must be high to enable the OSD mode, therefore black can’t be used in the OSD window. Load VP-P Blk. Level Shift 430Ω 3.62V +15 mV Applications of the LM1279A 390Ω 3.62V 0 mV Two demonstration boards are available to evaluate the LM1279A. One board is the pre-amp demonstration board. This board was used for testing and characterizing the LM1279A. The schematic for this board is shown in Figure 4 and the printed circuit layout for this board is shown in Figure 6. The other board is a complete video channel neck board that can be directly plugged into the CRT socket. The schematic for this board is shown in Figure 9 and the printed circuit layout is shown in Figure 10. The CRT driver used on this board is the LM2407. Any of National’s monolithic CRT 330Ω 3.58V −25 mV www.national.com 270Ω 3.51V −45 mV When using a lower load impedance, the LM1279A does go into hard clipping more quickly. This does reduce the headroom of the video output. Board layout is always critical in a high frequency application such as using the LM1279A. A poor layout can result in ringing of the video waveform after sudden transitions, or the part could actually oscillate. A good ground plane and proper routing of the +8V are important steps to a good PCB layout. The LM1279A does require very good coupling between 8 LM1279A Applications of the LM1279A (Continued) VCC1 and VCC2 (pins 2 and 16). This is clearly shown in Figure 6 and Figure 10 with the short and large trace between pins 2 and 16. Both demonstration boards offer the monitor designer an excellent example of good ground plane being used with the LM1279A. These boards are single sided, yet allow the LM1279A to operate at its peak performance. The neck board also shows a good example of interfacing to a CRT driver and to the CRT. The video signal path is kept as short as possible between the LM1279A and the CRT driver, and also between the CRT driver and the CRT socket. Actual performance of the LM1279A in the video pre-amp demonstration board is shown in Figure 7 and Figure 8. References Ott, Henry W. Noise Reduction Techniques in Electronic Systems, John Wiley & Sons, New York, 1976 Zahid Rahim, “Guide to CRT Video Design,” Application Note 861, National Semiconductor Corp., Jan. 1993 9 www.national.com LM1279A Applications of the LM1279A DS101250-13 FIGURE 6. LM1279A OSD Video Pre-Åmp Demontration Board Layout DS101250-16 DS101250-17 FIGURE 7. LM1279A Rise Time www.national.com FIGURE 8. LM1279A Fall Time 10 DS101250-14 (Continued) 11 LM1279A FIGURE 9. LM1279A/LM2407 Demonstration Neck Board Schematic Applications of the LM1279A www.national.com LM1279A Applications of the LM1279A (Continued) DS101250-15 FIGURE 10. LM1279A/LM2407 Demonstration Neck Board Layout www.national.com 12 LM1279A 110 MHz RGB Video Amplifier System with OSD Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM1279AN NS Package Number N20A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 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