* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Dee. 26, 195o E. FRANK Er`AL 2,535,912
Survey
Document related concepts
Electromagnetic compatibility wikipedia , lookup
Current source wikipedia , lookup
Time-to-digital converter wikipedia , lookup
Alternating current wikipedia , lookup
Mains electricity wikipedia , lookup
Chirp compression wikipedia , lookup
Buck converter wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Video camera tube wikipedia , lookup
Electrical grid wikipedia , lookup
Tube socket wikipedia , lookup
Opto-isolator wikipedia , lookup
Vacuum tube wikipedia , lookup
Cavity magnetron wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Transcript
Dee. 26, 195o E. FRANK Er'AL VIDEO GATING CIRCUIT Filed Dec. 8, 1948 ÜNE 2,535,912 2,535,912 Patented Dec. 26, 1950 UNITED STATES “ ÜFFICE 2,535,912 VIDEO GATING CIRCUIT Ernest Frank, Yeadon, Pa., and Robert Fred Mozley, Berkeley, Calif., assignors to the United States of America. as represented by the Secre tary of the United States Air Force Application December 8, 1948, Serial No. 64,138 4 Claims. (Cl. Z50-27) 1 2 This invention relates to gated viedo frequency amplifiers particularly as used in radar systems. In radar systems of the type in which short pulses of high frequencyV energy are radiated and the time intervals between the radiated pulses and reflected pulses from outlying targets are meas ured to determine the target ranges it is fre gate as a pedestal in the output signal of the am plifier or for allowing a pedestal of adjustable height to appear, as desired. The details of a specific embodiment of the in vention are shown inthe accompanying drawing in which Fig. 1 is a schematic diagram of the gated video quently desirable to limit the target presentation ampliñer and on >the screen, of the cathode ray indicator tube Fig. 2 shows several waveforms appearing in the circuit of Fig. l. Referring to Fig. 1 the video ampliñer com prises tWo ampliñer tubes, V2 and Va, connected in cascade. The negative video signal from the radar receiving equipment is applied to the con trol grid of tube V2 through condenser C3. This to those targets lying within `a given range. By so doing the resulting presentation contains only the targets of interest andv is,V considerably im proved by the elimination of other target reflec tions and a great amount of noise and background clutter. Automatic gun laying systems for use in - military aircraft usually employl such limitation thus restricting the display to only those targets signal may be of the form shown in Fig. 2(a) in within the usable range of the guns, say 5000 l2 and i3 represent reflections from targets. The time interval between radiated pulses is shown in which I0 represents the radiated pulse and Il, `yards'. 20 this figure to be 500 microseconds which corre 'The above described limitation is usually ac spends> to a pulse repetition rate of 2000 per second. rThis signal is ampliñed and reversed in phase by tube V2 and applied as a positive signal to the grid of tube Va. Since V3 is connected as a cathode follower the output signal taken from across load .resistor Re is likewise a positive signal. In order to gate the above described video am complished by rendering the video ampliñer which applies the received signals to the cathode-ray in-v dicator tube operative for a period of time after each radiated pulse just sufficient to allow reflec tions frorn targets up to 5000 yards, or other se lected distance, to be received. After this time interval the video amplifier becomes inoperative to apply signals'to the indicator tube until the occurrence of another radiated pulso. For tar pliñer the gating pulse` if’. in Fig. 1 is applied t0 gets up to 5000 yards this time interval is approxi- i mately 31 microseconds which is a small fraction the grid of tube V1 which is connected as a cathode follower and has a load impedance R1. This cathode follower stage acts as an impedance changing device so that the resulting positive of the time interval between radiated pulses which, for a 2000 pulse per second repetition rate, is 500 microseconds. In order to render the video ampliñer operative for the desired interval a rec- - tangular gating pulse is generated, the leading gate developed across resistor R1 appears to come from a source of very low internal impedance. A low output impedance is one of the Well known characteristics of a cathode follower stage and is due to negative feedback of the entire output voltage. The gating pulse may be generated in edge of which is coincident with the trailing edge of the radiated pulse ard the duration of which any desired` way and applied at any time as re is made equal to the time required for an elec tromagnetic Wave to travel to and return from a 40 quired by the use to which the amplifier is to be put. In the above described radar application target at the maximum range desired. In Ythe the gating pulse, as already mentioned, begins at case of a 5000 yard maximum range the gating the end of the radiated pulse and, in the case of pulse would have a duration of approximately a 5000 yard maximum range, has a length of 31 31 microseconds as stated above, microseconds. However, apparatus for generating It is the object of this invention to provide an and timing the gating pulse is not a part of this improved gated amplifier such as could be used invention. The. tube V2 is provided with a load in the above described application or in any ap impedance consisting of resistance Rv and induc plication requiring a high frequency amplifier tance Li. The> low signal potential end of in which may be rendered operative for short and precise intervals of time. The ampliñer has mini- ‘ ductance L1’ is connected through condenser C1 to the cathode of Vi and through diode V4 to a mum requirements as to the amplitude of the source of direct potential of +150 volts. The gating pulse due to the fact that a direct voltage in addition to the gating voltage is applied to the anode of the gated tube. Provisions are also made‘fo‘r either preventing the appearance ofthe l 5.5 output signal from amplifier V2 is applied through inductance L2 and blccking'condenser C4 to the grid of -cathode follower-stage Vs. The grid of 3 2,535,912 V3 is connected to an adjustable contact on poten tiometer R5 through high resistance R1 whereby an adjustable negative bias potential is applied thereto. The diode V5 shunts resistor R4 and to the sum of the anode voltage V2 and the volt age of the tap on Rs, with the polarity of the condenser voltage as indicated in the ligure. In the presence of a gating pulse the anode voltage prevents the grid from ever becoming more nega of V5 is elevated to a higher level during which tive than the adjustable tap on Rs. A diode used time condenser C4 charges to a higher level; in this manner is sometimes referred to as a however the increase in charge will be very slight clamping device since its clamps the applied wave due to the large time constant of C4 and R1 to the potential of the tap on R5. which, with C1 of the order of 0.02 microfarad In the absence of a gating pulse on the grid 10 and R4 of the order of 1 megohm, will be of the of V1 current flows from the +150 volt source order of .02 second or 20,000 microseconds, and through L1, R7 and the anode-cathode path of to the fact that the gating pulse lasts at the V2 to ground thus placing 2, positive potential on most for only 122 microseconds, and for 5000 the plate of V2 somewhat less than +150 volts de yards range for only 31 microseconds.' The gate pending upon the drop across R1. Also current 15 pedestal appearing on the anode of tube V2 is ñows around nthe circuit consisting of the +150 therefore for all practical purposes transferred volt source, diode V4, condenser C1 and resistor directly to the grid of tube Va. At the end of R1 until condenser C1 is charged to a voltage the gating pulse the anode potential drops to its equal to 150 volts minus the drop across V4 and original value and condenser C4 discharges to the normal steady state voltage across R1 due 20 its original voltage. However the discharge cur to the space current of V1. Since V1 has low rent passes through the low resistance afforded internal resistance and R1 has a low Value of by diode V5 rather than through high resistance 5000 to 10,000 ohms, which appears still lower R4, thus preventing any lowering of the grid po due to the feedback action in the associated cath tential of Vs below the value set by the position ode’ follower stage, the time constant of the 25 of the tap on R5. Tube V5 therefore in effect charging circuit for C1 is short and this con restores the direct component of the rectangular denser charges very rapidly. wave on the anode of V2 which could not be Due to the fact that a positive potential exists transmitted through condenser C4. on the anode of tube V2 in the absence of a gat Since video signal is continuously applied to ing pulse, as explained above, the tube acts dur 30 the control grid of V2 a resulting video signal ing this time to amplify and reverse the phase will appear in the output circuit of this tube oi the video signal applied to its grid. The re along the crest of the pedestal formed by the sulting positive video signal on the anode of gating pulse. This combined pedestal and video V2 is applied to the grid of V3; however no sig signal and its relation to the bias and cut-off nal appears at the output of V3 due to the fact voltages of V2 are shown in Fig. 2 (b). By pro that this tube is biased beyond its cut-off point, viding a bias potential from R5 of such value by the voltage from R5, by an amount greater that the pedestal just exceeds the cut-off point than the voltage of the maximum video signal of V3 a slight pedestal carrying the video signal applied to its grid so that the video signal, in occurring during the gate appears in the output the absence of a gate, is unable to cause con of V3 as shown in Fig. 2 (c). If desired, the duction in V3. This condition is shown graphi negative bias may be increased to the point where cally in Fig. 2(b) . the pedestal just reaches the cut-01T point in The application of a positive gating pulse to which case the video signal without the pedestal the grid of V1 causes a pulse of substantially appears in the output circuit. the same amplitude to appear across resistor 45 The inductances L1 and L2 in Fig. 1 may be R1. This voltage, acting through condenser C1 of the order of 100 and 400 microhenries respec and impedance L11-R7, raises the potential of tively and help to preserve the square wave form the anode of V2 by an amount equal to the pulse of the gate and resulting pedestal. ‘ voltage. Since the action of the gating pulse We claim as our invention: also raises the potential of the cathode of V1 50 1. A gated amplifier comprising a ñrst amplifier above that of the anode this diode becomes non tube and a second amplifier tube each having conductive thus isolating tube V2 from the +150 an anode, a cathode and a control grid, means volt supply during the gating pulse. Therefore, for applying a signal to be amplified between operating potential for the anode of tube V2 the control grid and cathode of said ñrst tube, in the presence of the gate comes from the volt 55 means for applying a positive direct potential ages across- R1 and C1 connected in series. Con between the anode and cathode of said ñrst tube, denser C1 should be large enough to hold its means for applying a positive rectangular gating charge and voltage substantially at full value pulse to the anode of said ñrst tube, means for during the gating pulse. The size of C1 there applying the gating pulse and amplified signal fore depends on the resistance in its discharge 60 on the anode of said ñrst tube to the grid of said circuit which includes R1, R'z and the plate re second tube, a source of operating potential and sistance of V2. In a circuit of the type shown a load impedance connected between the anode a capacity of 0.25 microfarad for C1 is ample for and cathode of said second tube, means for con gating pulses up to 122 microseconds, which cor necting anY output circuit across said load imped responds to a range of 20,000 yards. In order 65 ance, and means independent of the signal on to have the anode potential of V2 follow the gat the grid of said second tube for biasing the grid ing pulse closely the time constants of the anode of said second tube neagtive with respect to the circuit should be small. This will be realized in cathode of said second tube by a ñxed amount the circuit shown because of the comparatively equal to the cut-oli voltage of said tube plus a low value of Rv, which may be of the order of 70 voltage greater than the maximum signal applied 10,000 ohms, and the very small capacity be to said grid in the absence of a gating pulse and tween the anode of V2 and ground. equal to or less than the amplitude of the gating During the absence of a gating pulse and with pulse applied to said grid from the anode of the circuit of Fig. 1 in a stable condition the said ñrst tube. - _. "condenser C1 will be charged to a voltage equal 75. V2A gated amplifier comprising a first ampli; 2,535,912' 5 lier tube having an anode, a cathode and a con trol grid, means connecting the cathode of said 6 the gating pulse and signal appearing on the anode of said ñrst tube are applied to the grid of said second tube, means including a high re first tube to a point of reference potential, a load sistance connected between the grid of said sec impedance having one end connected to the anode of said ñrst tube and the other` end con UX ond tube and a point having a, negative potential with respect to said reference point said negative nected to the cathode of a diode rectifier tube, potental having a value equal to the cut-olf volt a source of direct current having its positive age of said second tube plus a voltage greater terminal connected to the anode of said diode than the maximum signal applied to the grid of and its negative terminal connected to said point of reference potential, a condenser having one 10 said second tube in the absence of a gating pulse and equal to or less than the amplitude of the terminal connected to the cathode of said diode, gating pulse applied to said grid from the anode means having a low internal impedance for ap of said ñrst tube. plying a positive rectangular gating pulse be 3. Apparatus as claimed in claim 2 in which tween the other side of said condenser and said point of reference potential, said condenser being 15 said rectangular gating pulse applying means is a cathode follower stage. of sufücient capacity that the time constant of 4, Apparatus as claimed in claim 3 in which the circuit including said condenser, said load a diode is connected in shunt to the high resist impedance, the plate impedance of said first tube ance connected between the grid of said second and the internal impedance of said pulse apply ing means is long compared to the duration of 20 tube and said point of negative potential and in which said last named diode is poled to conduct said gating pulse, means for applying a signal toward said grid. to be amplified between the grid and cathode » ERNEST FRANK. of said first tube, a second amplifier tube having ROBERT FRED MOZLEY. an anode, a cathode and a control grid, means connecting the anode of said second tube to the 25 REFERENCES CITED positive terminal of a source of direct current the negative terminal of which is connected to The following references are of record in the said point of reference potential, means con ille of this patent: necting the cathode of said second tube through UNITED STATES PATENTS a load impedance to said point of reference po 30 Number Name Date tential, coupling means including a blocking con 1,912,234 Willoughby ______ __ May 30, 1933 denser connected between the anode of said first 2,132,655 Smith ____________ _- Oct. 11, 1938 tube and the grid of said second tube whereby