4707 dey road liverpool, n.y. 13088 m.s.kennedy corp. (315) 701-6751 features: negative output voltage for grid drive 2ns transition times drives 8.5pf capacitive load with ease dc coupled for output level adjust 175mhz bandwidth 55vpp output swing replacement for cr2424r wide bandwidth, high voltage crt video amplifier equivalent schematic iso 9001 certified by dscc 642 description: the msk 642(b) is a wide bandwidth, high voltage color or monochrome crt video amplifier designed specifically to drive the grid of today's most demanding high resolution crt monitors. the msk 642(b) is a transimpedance amplifier capable of achieving a 25v output voltage swing with an input current of 9.3ma. the output of the amplifier is dc biased at half the power supply voltage. transition times in the range of 2ns enable the msk 642 to drive 10ns pixels with ease and make it ideally suited for monitors with 1280 x 1024 or higher display resolutions. the msk 642 is mounted in a space efficient 9 pin single in-line bathtub package with heat sink fins. crt driver for color and monochrome monitors high voltage transimpedance amplifier ultra high speed amplifier for test equipment typical applications -vee ground ground output 1 2 3 4 5 inverting input ground ground -vee -vee 6 7 8 9 pin-out information mil-prf-38534 certified rev. b 8/00 1
-75v 10.5c/w 250ma 1 2 3 4 5 6 group a subgroup 1 2 3 1 2,3 1 2,3 - - 4 4 4 4 4 - - - 4 v in =n/c v in =n/c v in =n/c v in =0.7v derated performance f=10khz f=10khz v in =2v pp ; f=10khz v out =40v pp v out =40v pp v out =20v pp v out =20v pp f=1khz f=10khz; 5v pp v out 50v pp -65c to +150c 300c -40c to +85c -55c to +125c 175c absolute maximum ratings t st t ld t c t j storage temperature range lead temperature range (10 seconds) case operating temperature MSK642 MSK642b junction temperature supply voltage thermal resistance (junction to case) peak output current -v ee q jc i out r in =215 w , c in =100pf, c load =8.5pf, r l = , unless otherwise specified (see figure 1). guaranteed by design but not tested. typical parameters are representative of actual device performance but are for reference only. industrial grade devices shall be tested to subgroups 1 and 4 unless otherwise specified. military grade devices ('b' suffix) shall be 100% tested to subgroups 1,2,3 and 4. subgroup 5 and 6 testing available upon request. subgroup 1,4 t a =t c =+25c subgroup 2,5 t a =t c =+125c subgroup 3,6 t a =t c =-55c typ. -40 -55 -35 -1.55 - -30 - 10 -60 -58 -2 12.5 2.1 2 25 175 - 0.5 typ. -40 -55 -35 -1.55 - -30 -30 10 -60 -58 -2 12.5 2.1 2 25 175 - 0.5 static power supply current input bias voltage output offset voltage input capacitance power supply range dynamic characteristics output voltage high output voltage low voltage gain rise time fall time overshoot (adjustable) -3db bandwidth low frequency tilt voltage linearity error min. - - - -1.4 -1.35 -28 -26 - -40 -55 - 10.5 - - - 130 - - max. -45 -65 -45 -1.7 -1.8 -32 -34 - -75 - -5 14.5 2.9 2.9 - - 1.5 5 min. - - - -1.3 - -27 - - -40 -55 - 10 - - - 125 - - max. -50 - - -1.8 - -33 - - -70 - -5 15 3 3 - - 1.5 5 msk 642b msk 642 parameter test conditions electrical specifications -vee=-60v unless otherwise specified 2 2 2 2 1 ma ma ma v v v v pf v v v v/v ns ns % mhz v % units notes: rev. b 8/00 2
typical test circuit the signal source in figure 1 can be either a fast pulse gen- erator or a network analyzer as long as the output impedance is 50 ohms. the dc level of the input should be -1.55v and all cables should be kept as short as possible. since total load capacitance should be kept below 8.5pf, a fet probe should be used on the ouput. using the msk 642 the output of the amplifier is biased at one half of the power supply voltage. an output voltage swing of 25 volts is typi- cal with a power supply voltage of -60 volts. with an 8.5pf capacitive load, transistion times are in the 2.1ns range. if a spark gap current limiting resistor is used on the output of the amplifier and the transistion times are degraded, a peaking coil may be used to preserve system performance. the optimum value for this coil will be in the range of 100 to 200nh and can best be determined by trial and error. the output of the msk 642 is not short circuit protected, therefore, purely resistive loads should be no less than 600 ohms at any time to avoid damaging the output. operation considerations the input of the msk 642 rests at a -1.55vdc level with the input terminal open. in this state, the output rests at one half of the power supply voltage. when connecting a pulse genera- tor to the input of the amplifier, the dc level should be offset so that the signal is centered around -1.55v. during character- ization, the input should be coupled to the msk 642 through a parallel combination of a variable resistor and variable capacitor peaking circuit. optimum values for the peaking circuit can be determined experimentally. the optimum value of load capaci- tance is 8.5pf. viewing the output with a normal oscilloscope probe would seriously degrade performance. a fet probe fit- ted with a 100:1 voltage divider will add only approximately 1.5pf of capacitance to the load and is highly recommended. an experimental circuit along with recommended values can be found in figure 2. application notes output issues the output of the msk 642 is a pair of bipolar emitter follow- ers configured in a complimentary push pull configuration. this configuration eliminates the need for a pull up load resistor and makes the amplifier less susceptible to load capacitance varia- tions. connecting a wire or cable from the output of the ampli- fier to the crt grid can create a resonant circuit which can cause unwanted oscillations or overshoot at its resonant fre- quency. a damping resistor in series with the lead inductance will alleviate this condition. the optimum value of this resistor can be determined using the following formula: r = 2* ? l/c this resistor also doubles as an arcing protector. in the bread- boarding stage, the value of this resistor should be determined experimentally. resistance in the range of 50 to 100 ohms is usually sufficient. if a quick, simple peaking network is de- sired, a 300 ohm cable terminated by a capacitor will act like an inductor in the frequency range involved. heat sinking the msk 642 requires heat sinking in most applications. the following formula may be applied to determine if a heat sink is necessary and what size and type to use. r q sa = ((tj-ta)/pd ) - (r q jc) - (r q cs) where tj = junction temperature pd = total power dissipation r q jc = junction to case thermal resistance r q cs = case to heat sink thermal resistance r q sa = heat sink to ambient thermal resistance tc = case temperature ta = ambient temperature ts = sink temperature example tj = 150c ta = 100c pd = 3w r q jc = 10.3c/w r q cs = 0.15c/w solving the above equation for r q sa (heat sink thermal conduc- tivity) shows that the heat sink for this application must have a thermal resistance of no more than 6.2c/w to maintain a junc- tion temperature of no more than 150c. transimpedance amplification transimpedance amplifiers relate input current to output volt- age. the msk 642 contains an internal 3k w feedback resistor. this resistor converts input current to output voltage in the following manner (see figure 1): 1.43v (referenced to -1.55vdc) across the 215 w input resistor results in an input current of 6.65ma. this current flows through the 3k w feedback resistor and results approxi- mately in a 20v swing at the output. the actual voltage gain of the typical msk 642 circuit may be slightly less due to tran- sistor losses. the following formula approximates voltage gain including potential losses: voltage gain (v/v) = 3k w /(rin + l) l ? 25 w rev. b 8/00 3
typical performance curves rev. b 8/00 4
complete video system figure 3 above illustrates how an msk 620 and msk 642 can be used to build a compete video system for high voltage grid drive. ra and rb act as a level shift stage to match the +3.9vdc level at the output of the msk 620 with the -1.55vdc level at the input of the msk 642. the output of the msk 642 is sampled and fed back to the msk 620. this scheme provides black level control superior to sampling the signal at pin 14 of the msk 620. the general rule of thumb for transition times for a video d river is that rising and falling edges should be no more than one third the pixel time of the monitor. to improve rise and fall time in the system, the peaking capacitor cp was added across the input resistor of the msk 642. at high frequencies cp increases the gain of the amplifier there by causing peaking. cp should be a variable capacitor so that the response of the amplifier can be fine tuned for minimum transition time with minimum ringing. rev. b 8/00 5
ordering information screening level MSK642 industrial the information contained herein is believed to be accurate at the time of printing. msk reserves the right to make changes to its products or specifications without notice, however, and assumes no liability for the use of its products. mechanical specifications m.s. kennedy corp. 4707 dey road, liverpool, new york 13088 phone (315) 701-6751 fax (315) 701-6752 www.mskennedy.com MSK642b military-mil-prf-38534 all dimensions are 0.010 inches unless otherwise labeled note: esd triangle indicates pin 1. part number rev. b 8/00 6
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