Patent GB-1241729-A (GB)
Title: Rotational straight display line generator
IPC: G09G1/08
Filed: 1969-06-11
Abstract: 1,241,729. Cathode-ray tube circuits; transistor sawtooth circuits. BENDIX CORP. 11 June, 1969 [17 June, 1968], No. 29617/69. Headings H3T and H4T. In an arrangement for deflecting the beam of a cathode-ray display tube to trace a straight line passing through a fixed point about which it is rotatable in correspondence with the angular displacement of the operating means of a signal source supplying two electrical signal outputs which are functions, respectively, of the sine and of the cosine of such angular displacement, each of the signal outputs is periodically integrated by, respective, simultaneously operating means the outputs of each of which are combined with a respective one of the signal outputs which forms the input to the respective integrating means and the two sets of combined signals fed to respective orthogonal deflecting means for the beam of the tube. The invention is described in connection with the display in an aircraft of a "horizon" line which rotates about its centre point in correspondence with rotation of the aircraft about its longitudinal axis (i.e. the roll axis). Referring to Fig. 1, the roll of the aircraft is sensed by a vertical gyro (not shown) coupled by shaft 4 to the rotor 2 of a Synchro 1 connected to a transolver 10 which supplies A.C. output voltages proportional to the sine and to the cosine of the angle of roll on conductors 14 and 14A respectively. These A.C. voltages are then demodulated in respective demodulators 18, 18A the D.C. outputs of which are utilized to produce the Y and X-deflection quantities, respectively. Considering the production of the Y-deflection quantity (the production of the X- deflection quantity being identical), the output of demodulator 18 is fed via a resistor 21 to an operational amplifier 25 which with a capacitor 31 and a MOS field-effect transistor 35 constitute an integrator. The transistor 35, which shunts capacitor 31 and is normally conducting, is rendered non-conducting periodically (for a duration of 640 microseconds repeated 49 times per second) by switching pulses E2 from a timing source 47 so that a ramp voltage is produced at the output of amplifier 25 by the charging of capacitor 31 via resistor 21 by the D.C. voltage output of demodulator 18 and this ramp voltage is supplied via resistor 43 to the (+) input of a differential amplifier 70. When transistor 35 is rendered non-conducting a second MOS fieldeffect transistor 54, which is normally non- conducting, is simultaneously rendered conducting by pulses El (of the same duration and repetition frequency as pulses E2) from source 47 and passes the output of demodulator 18 to the (-) input of differential amplifier, 70 via resistor 67. The switching of transistors 35 and 54 by the pulses E2 and E1 respectively thus results in a sawtooth wave of maximum amplitude proportional to the D.C. voltage output of demodulator 18 (and therefore proportional to the sine of the angle of roll) being supplied over conductor 42 and resistor 43 to the (+) input of amplifier 70 and the application of a rectangular wave voltage having an amplitude equal to the maximum amplitude of the sawtooth wave being supplied over conductor 65 and resistor 67 to the (-) input of amplifier 70, the waveforms on conductors 42 and 65 for various values of the angle of roll being shown in Fig. 4. The resistor 67 and the feed-back resistor 73 each has a value equal to twice that of resistor 43 so that amplifier 70 produces a gain of x 2 in the (+) channel and a gain of x 1, with polarity reversal, in the (-) channel resulting in the two input waveforms being combined to produce an output which is supplied via a third MOS field-effect transistor 60 (switched on by the pulses El) to an operational amplifier 82 the output from which on conductor 88 has the form shown in Fig. 4 for various angles of roll. Such output is utilized to produce the Y-deflection via driver amplifier 90 and the output on conductor 88A (see also Fig. 4) produced in an identical manner to that on conductor 88 is utilized to produce the X-deflection of the display tube via driver amplifier 90A. The tube may operate with electromagnetic deflection as shown at 96 or an electrostatically deflected tube may be employed (Fig. 2, not shown). Since the display of the artificial horizon line is effected during a period of 640 microseconds repeated 49 times per second a period of 968À64 milliseconds is available during each second for interscan (multiple) displays. The operational amplifiers 82, 82A are used to create a high resistance to eliminate errors due to changes in resistance caused by the switching effect of transistors 60, 60A, and may be omitted if the arrangements of the invention is not used in a multiple display system.