LM1201

LM1201 Video Amplifier System January 1995 LM1201 Video Amplifier System General Description The LM1201 is a wideband video amplifier system intended for high resolution monochrome or RGB monitor applications In addition to the wideband video amplifier the LM1201 contains a gated differential input black level clamp comparator for brightness control and an attenuator circuit for contrast control The LM1201 also contains a voltage reference for the video input For medium resolution RGB color monitor applications also see the LM1203 Video Amplifier System data sheet Y Y Y Provisions for external gain set and peaking of video amplifier Video input voltage reference Low impedance output driver Typical Applications Y Y Y Y Y Features Y Y Y Y Y Y b 3 dB) Wideband video amplifier (200 MHz Attenuator circuit for contrast control (l40 dB range) Externally gated comparator for brightness control CRT video amplifiers Video switches High frequency video preamplifiers Wideband gain controls PC monitors Workstations Facsimile machines Printers Block and Connection Diagram TL H 10006 – 1 FIGURE 1 Order Number LM1201M or LM1201N See NS Package Number M16A or N16E C1996 National Semiconductor Corporation TL H 10006 RRD-B30M56 Printed in U S A Absolute Maximum Ratings If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Supply Voltage VCC Pins 10 12 15 to Ground Pins 1 7 Voltage at Any Input Pin (VIN) 13 5V Storage Temperature Range (TSTG) Lead Temperature (Soldering 10 sec ) b 65 C to a 150 C 265 C VCC t VIN t GND Video Output Current (I8) 28 mA 1 56W Package Power Dissipation at TA e 25 C (Above 25 C derate based on (iJA and TJ) 80 C W Package Thermal Resistance (iJA) N16E Package Thermal Resistance (iJA) M16A 100 C W Junction Temperature (TJ) 150 C ESD Susceptibility 2 kV Human body model 100 pF discharged through a 1 5 kX resistor Operating Ratings (Note 4) Temperature Range Supply Voltage (VCC) 0 C to a 70 C 10 8V s VCC s 13 2V Electrical Characteristics See Test Circuit (Figure 2) DC Static Tests S9 Open Symbol IS V3 Parameter Supply Current Video Input Reference Voltage TA e 25 C VCC1 e VCC2 e VCC3 e 12V V4 e 6V V5 e 0V V6 e 2 0V unless otherwise stated Tested Limit (Note 1) 57 24 2 95 Design Limit (Note 2) Units (Limits) mA(max) V(min) V(max) mA(max) V(min) V(max) mA(max) mA(max) mA(min) mA(min) V(max) V(min) mV(max) Conditions VCC Pins 12 15 Only Typical 45 2 65 I16 V5L V5H I5L I5H I2 a I2 b V8L V8H VOS Video Input Bias Current Clamp Gate Low Input Voltage Clamp Gate High Input Voltage Clamp Gate Low Input Current Clamp Gate High Input Current Clamp Cap Charge Current Clamp Cap Discharge Current Video Output Low Voltage Video Output High Voltage Comparator Input Offset Voltage (V3 – V16) 10 kX Clamp Comparator On Clamp Comparator Off V5 e 0V V5 e 12V V2 e 0V V2 e 5V V2 e 0V V2 e 5V V6 – V9 50 12 16 b0 5 20 08 20 b5 0 0 005 1 b1 1 0 55 b 0 55 05 85 g0 5 09 80 g 25 AC Dynamic Tests S9 Closed Symbol Av max DAv 5V DAv 2V THD f (b3dB) tr tf Parameter Video Amplifier Gain Attenuation Attenuation 5V 2V V5 e 0V V6 e 4V Conditions V4 e 12V Ref Av max V4 e 5V Ref Av max V4 e 2V V4 e 5V VO e 1 Vp-p V4 e 12V VO e 100 mVrms VO e 4 Vp-p VO e 4 Vp-p Typ 8 b 10 b 45 Tested Limit (Note 1) 55 Design Limit (Note 2) Units (Limits) V V(min) dB dB % Video Amplifier Distortion Video Amplifier Bandwidth (Note 3) Output Rise Time (Note 3) Output Fall Time (Note 3) 03 200 25 3 170 MHz(min) ns ns Note 1 These parameters are guaranteed and 100% production tested Note 2 Design limits are guaranteed (but not 100% production tested) These limits are not used to calculate outgoing quality levels Note 3 When measuring video amplifier bandwidth or pulse rise and fall times a double sided full ground plane printed circuit board without socket is recommended Note 4 Operating Ratings indicate conditions of which the device is functional but does not guarantee specific performance limits For guaranteed specifications and test conditions see 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 http www national com 2 TL H 10006 – 2 FIGURE 2 LM1201 AC DC Test Circuit Note When V5 s 0 8V and S9 is closed DC feedback around the Video Amplifier is provided by the clamp comparator Under these conditions sine wave or 50% duty cycle square waves can be used for test purposes The low frequency dominant pole is determined by C2 at Pin 2 Capacitor C9 at pin 9 prevents overloading the clamp comparator inverting input See applications section for additional information TL H 10006 – 3 FIGURE 3 Typical Application of the LM1201 30X resistor is added to the input pin for protection against current surges coming from the 10 mF input capacitor By increasing this resistor to well over 100X the rise and fall times of the LM1201 can be increased for EMI considerations 3 http www national com APPLICATIONS INFORMATION Figure 4 shows the block diagram of a typical analog monochrome monitor The monitor is used with CAD CAM work stations PCs arcade games and in a wide range of other applications that benefit from the use of high resolution display terminals Monitor characteristics may differ in such ways as sweep rates screen size or in video amplifier speed but will still be generally configured as shown in Figure 4 Separate horizontal and vertical sync signals may be required or they may be contained as a composite signal in the video input signal The video input signal is usually supplied by coaxial cable which is terminated in 75X at the monitor input and internally AC coupled to the video amplifier The input signal is approximately 1V peak-to-peak in amplitude and at the input of the high voltage video section approximately 6V peak-to-peak At the cathode of the CRT the video signals can be as high as 60V peak to peak The block in Figure 4 labeled ‘‘Video Amplification with DC Controlled Gain Black Level’’ contains the function of the LM1201 video amplifier system TL H 10006 – 4 FIGURE 4 Typical Monochrome Monitor Block Diagram http www national com 4 Circuit Description Figure 5 is a block diagram of the LM1201 along with the contrast and brightness controls The contrast control is a DC operated attenuator which varies the AC gain of the amplifier without introducing any signal distortions or DC output shift The brightness control function requires a ‘‘sample and hold’’ circuit (black level clamp) which holds the DC bias of the video amplifier and CRT cathodes constant during the black level reference portion of the video waveform The clamp comparator when gated on during this reference period will charge or discharge the clamp capacitor until the non-inverting input of the clamp comparator matches that of the inverting input voltage which was set by the brightness control Figure 6 is a simplified schematic of the LM1201 video amplifier along with the recommended external components The IC pin numbers are circled with all external components shown outside of the dashed line The video input is applied to pin 16 via the 10 mF coupling capacitor DC bias to the video input is through the 10 kX resistor which is connected to the 2 6V reference at pin 3 The low frequency roll-off of the amplifier is set by these two components Transistor Q1 buffers the video signal to the base of Q2 The Q2 collector current is then directed to the VCC1 supply through Q3 or to VCC2 through Q4 and the 500X load resistor depending upon the differential DC voltage at the bases of Q3 and Q4 The Q3 and Q4 differential base voltage is determined by the contrast control circuit which is described below The black level DC voltage at the collector of Q4 is maintained by Q5 and Q6 which are part of the black level clamp circuit also described below The video signal appearing at the collector of Q4 is then buffered by Q7 and level shifted down by Z1 and Q8 to the base of Q9 which will then provide additional system gain TL H 10006 – 5 FIGURE 5 Block Diagram of LM201 Video Amplifier with Contrast and Black Level Control 5 http www national com http Circuit Description (Continued) www national com TL H 10006 – 6 6 FIGURE 6 Simplified LM1201 Video Amplifier Section with Recommended External Components Circuit Description (Continued) The ‘‘Drive’’ pin will allow the user to set the maximum gain of the amplifier based on the range of input video signal levels and the CRT stage gain if it is fixed or limited When using three LM1201 devices for high resolution RGB applications the ‘‘Drive’’ pin allows the user to trim the gain of each channel to correct for differences in the three CRT cathodes A small capacitor (12 pF) in shunt with a 51X drive resistor at this pin will extend the high frequency gain of the video amplifier by compensating for some of the internal high frequency roll off The 51X resistor will set the system gain to approximately 8 or 18 dB The video signal at the collector of Q9 is buffered and level shifted down by Q10 and Q11 to the base of the output emitter follower Q12 Between the emitter of Q12 and the video output pin is a 50X resistor which is included to prevent spurious oscillations when driving capacitive loads An external emitter resistor must be added between the video output pin and ground The value of this resistor should not be less than 330X otherwise package power limitations may be exceeded when worst case (high supply max supply current max temp) calculations are made If negative going pulse slewing is a problem because of high capacitive loads ( l10 pF) a more efficient method of emitter pull down would be to connect a suitable resistor to a negative supply voltage This has the effect of a current source pull down when the minus supply voltage is b12V and the emitter current is approximately 10 mA The system gain will also increase slightly because less signal will be lost across the internal 50X resistor Precautions must be taken to prevent the video output pin from going below ground since IC substrate currents may cause erratic operation The collector current from the video output transistor is returned to the power supply at VCC3 pin 10 When making power dissipation calculations note that the datasheet specifies only the VCC1 and VCC2 supply currents at 12V The IC power dissipation contribution of VCC3 is dependent upon the video output emitter pull down load In normal operation the minimum black level voltage that can be set at the video output pin is approximately 2V at maximum contrast setting In applications that require a lower black level voltage a resistor (approximately 16 kX) can be added from pin 3 to ground This has the effect of raising the DC voltage at the collector of Q4 which will extend the range of the black level clamp by allowing Q5 to remain active In applications that require video amplifier shutdown due to fault conditions detected by monitor protection circuits pin 3 and the wiper arms of the contrast and brightness controls can be grounded without harming the IC This assumes some series resistance between the top of the control potentiometers and VCC Figure 7 shows the internal construction of the pin 3 2 6V reference circuit which is used to provide temperature and supply voltage tracking compensation for the video amplifier input The value of the external DC biasing resistors should not be larger than 10 kX when using more than one LM1201 (e g in RGB systems) because minor differences in input bias currents on the individual video amplifiers may cause offsets in gain TL H 10006 – 7 FIGURE 7 LM1201 Video Input Voltage Reference and Contrast Control Circuits 7 http www national com Circuit Description (Continued) Figure 7 also shows how the contrast control circuit is configured Resistors R23 R24 diodes D3 D4 and transistor Q13 are used to establish a low impedance zero TC half supply voltage reference at the base of Q14 The differential amplifier formed by Q15 Q16 and feedback transistor Q17 along with resistors R27 R28 establish a differential base voltage for Q3 and Q4 in Figure 6 When externally adding or subtracting current from the collector of Q16 a new differential voltage is generated that reflects the change in the ratio of currents in Q15 and Q16 To provide voltage control of the Q16 current resistor R29 is added between the Q16 collector and pin 4 A capacitor should be added from pin 4 to ground to prevent noise from the contrast control pot from entering the IC Figure 8 is a simplified schematic of the clamp gate and clamp comparator section of the LM1201 The clamp gate circuit consists of a PNP input buffer transistor (Q18) a PNP emitter coupled pair referenced on one side to 2 1V (Q19 Q20) and an output switch (Q21) When the clamp gate input at pin 5 is high (l1 5V) the Q21 switch is on and shunts the I1 1mA current to ground When pin 5 is low (k1 3V) the Q21 switch is off and the I1 1mA current source is mirrored or ‘‘turned around’’ by reference diode D5 and Q26 to provide a 1mA current source for the clamp comparator The inputs to the comparator are similar to the clamp gate input except that an NPN emitter coupled pair is used to control the current which will charge or discharge the clamp capacitor at pin 2 PNP transistors are used at the inputs because they offer a number of advantages over NPNs PNPs will operate with base voltages at or near ground and will usually have a greater reverse emitter-base breakdown voltage (BVebo) Because the differential input voltage to the clamp comparator during the video scan period could be greater than the BVebo of NPN transistors resistor R34 with a value one half that of R33 or R35 is connected between the bases of Q23 and Q27 This resistor will limit the maximum differential input to Q24 Q25 to approximately 350 mV The clamp comparator common mode range extends from ground to approximately 9V and the maximum differential input voltage is VCC and ground TL H 10006 – 8 FIGURE 8 Simplified Schematic of LM1201 Clamp Gate and Clamp Comparator Circuits http www national com 8 Applications Information Figure 9 shows the configuration of a high frequency amplifier with non-gated DC feedback Pin 5 is tied low to turn on the clamp comparator (feedback amplifier) The inverting input (pin 9) is connected to the amplifier output from a low pass filter Additional low frequency filtering is provided by the clamp capacitor The Drive pin is grounded to allow for the widest range of output signals Maximum output swing is achieved when the DC output is set to approximately 4 5V TL H 10006 – 9 FIGURE 9 High Frequency Amplifier Attenuator Circuit with Non-Gated DC Feedback (Non-Video Applications) 9 http www national com Applications Information (Continued) Figure 10 shows the LM1201 set up as a video amplifier with biphase outputs Because the collector of output transistor Q12 is the only internal connection to VCC3 a 75X termination to the power supply voltage allows one to obtain inverted video at pin 10 Black level on the non-inverted video output (pin 8) is set to 1 5V by the voltage divider on pin 6 Figure 11 shows how a high frequency video switch may be designed using multiple LM1201 devices All outputs can be OR’ed together assuming no more than one channel is selected at any given time Channel selection is accomplished by keeping the appropriate SELECT SWITCH open Closing the SELECT SWITCH on a given channel disables that channel’s output (pin 8) leaving it in a high impedance state A single pair of contrast and brightness potentiometers control the selected channel’s gain and output DC level TL H 10006 – 10 FIGURE 10 Preclamped Video Amplifier with Biphase Outputs http www national com 10 Applications Information (Continued) TL H 10006 – 11 FIGURE 11 High Frequency Video Switch with Common Contrast and Brightness Controls 11 http www national com Rise Time No Socket Rise Time In Socket TL H 10006–12 TL H 10006 – 13 Fall Time No Socket Fall Time In Socket TL H 10006–14 TL H 10006 – 15 HP8082 pulse generator HP10241A 10 1 voltage divider HP1120A 500 MHz FET probe Tektronix 2465A 350 MHz scope  Actual output signal swings 4 Vp-p (10 1 divider is used) Contrast is set to maximum VIN e 500 mVp-p RDRIVE e 50X Vertical scale is actually 1V div and not 100 mV div due to 10 1 attenuator used  Outputs are centered at 4V DC     Scale for All Photos Vert 1V Div Horiz 5 ns Div http www national com 12 TL H 10006 – 16 Note The p c b layout shown above is suitable for evaluating the performance of the LM1201 Although it is similar to the typical application circuit of Figure 3 there is no c r t driver stage Instead a feedback resistor is connected between Pins 8 and 9 and the brightness control is connected to Pin 6 Again for best results a socket should not be used for the LM1201 COMPONENT VALUES R1 75X 5% 1 4 watt carbon composition C1 0 1 mF ceramic R3 10 kX 5% 1 4 watt carbon composition C2 0 1 mF ceramic R4 50X 5% 1 4 watt carbon composition C4 0 1 mF ceramic R5 200X 5% 1 4 watt carbon composition C5 0 1 mF ceramic R6 75X 5% 1 4 watt carbon composition C6 10 mF 6V electrolytic R7 330X 5% 1 4 watt carbon composition C7 0 1 mF ceramic R8 680 kX 5% 1 4 watt carbon composition C8 0 1 mF ceramic R9 10 kX trim pot helitrim model 91 C9 0 1 mF ceramic R10 5 1 kX 5% 1 4 watt carbon composition C10 0 1 mF ceramic R11 43 kX 5% 1 4 watt carbon composition C11 0 1 mF ceramic R12 12 kX 5% 1 4 watt carbon composition C12 0 1 mF ceramic R13 10 kX trim pot helitrim model 91 C13 100 mF 15V electrolytic R14 2 kX 5% 1 4 watt carbon composition C14 0 001 mF mica R15 200X 5% 1 4 watt carbon composition C15 0 1 mF ceramic IC1 IC2 LM1201 LM1881 13 http www national com http www national com 14 Physical Dimensions inches (millimeters) unless otherwise noted 16-Lead (0 1500 Wide) Small Outline Molded Package (M) Order Number LM1201M NS Package Number M16A 15 http www national com LM1201 Video Amplifier System Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Lit 107313 16-Lead Molded Dual-In-Line Package (N) Order Number LM1201N NS Package Number N16E 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 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 National Semiconductor Corporation 1111 West Bardin Road Arlington TX 76017 Tel 1(800) 272-9959 Fax 1(800) 737-7018 2 A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness http www national com National Semiconductor Europe Fax a49 (0) 180-530 85 86 Email europe support nsc com Deutsch Tel a49 (0) 180-530 85 85 English Tel a49 (0) 180-532 78 32 Fran ais Tel a49 (0) 180-532 93 58 Italiano Tel a49 (0) 180-534 16 80 National Semiconductor Hong Kong Ltd 13th Floor Straight Block Ocean Centre 5 Canton Rd Tsimshatsui Kowloon Hong Kong Tel (852) 2737-1600 Fax (852) 2736-9960 National Semiconductor Japan Ltd Tel 81-043-299-2308 Fax 81-043-299-2408 National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications