Patent GB-1139392-A (GB)
Title: Improvements in and relating to an electrical circuit comprising a constant current pulse generating circuit
IPC: H03K5/00
Filed: 1967-03-21
Abstract: 1,139,392. Transistor saw-tooth and pulse circuits. INTERNATIONAL BUSINESS MACHINES CORP. 21 March, 1967 [30 March, 1966], No. 13069/67. Heading H3T. [Also in Divisions G1 and G3] A load 6, e.g. a transistor under test (see Division G1) is supplied with a pulse of constant current for a perdetermined time by means of the circuit shown, in which a pulse generator 1 having a voltage output of controllable amplitude controls a current generator 5 whose output is sensed by a detector 8 supplying a signal to a control circuit 9 which is also supplied from 10 with a predetermined reference signal, the arrangement being such that when the output of generator 5 reaches a predetermined value, circuit 9 produces a signal at output 25 to lock the generator 1 at that particular voltage output and so maintain the output of generator 5 constant at the predetermined value. Thereafter transistors 27, 28 respond to changes in current caused by impedance variation of the load 6 and so maintain the current constant. A typical cycle of operation is as follows:- (1) With positive potential at the terminals 2, 3, transistor 26 is reverse biased by the output of amplifier 16 so that there is no output from generator 5 and amplifier 39, the latter condition causing transistor 52 to be conducting, multivibrator 61 to be passive and its output at 25 to be negative.  (2) Pulse reversal at terminal 2 reverse biases the diode 11 to stop the forward current through diode 13. (3) Pulse reversal at terminal 3, shortly after that at terminal 2, Fig. 3 (not shown), cuts off diode 20 and produces output from amplifier 16 in the form of a linear ramp whose rate of rise is adjustable by a resistor 23. A current of like waveform is thus produced at the output 34 of the generator 5 in which members 26, 31 form a voltage follower, a Zener diode 32 holds the base of transistor 28 at constant potential and the voltage of the constant voltage source 30 is divided between resistor 38 (of detector 8), the load 6 and the drop from the collector of transistor 28 to a common reference 17. (4) When the output Vs from amplifier 39 equals the reference voltage (-)Vp, the bias current IB from transistor 47 switches a tunnel diode 43 and turns on transistor 44, which causes transistor 52 to turn off and the multivibrator 61 to produce a positive pulse at the terminal 25. As a result diode 21 conducts to cut-off the diode 12 and the condenser 19 holds its charge for the remaining duration of the pulse at terminal 2, due to the high impedance of members 11, 12, 13 and 16. Thus transistor 26 is biased at a fixed value and the output current of generator 5 is maintained constant. (5) When the pulse at terminal 2 returns to its positive value, diode 11 is forward biased to discharge condenser 19, forward bias diode 13, and so cut off transistor 26 and the output from generator 5. In a modification employing an amplifier 16 of low output impedance, Fig. 2(b) (not shown), an output amplifier (120) is connected between the output of the generator 1 and the input of the generator 5. Also, the amplifier 39 may be replaced by a composite amplifier comprising two amplifiers appropriately connected with one another and with resistors, Fig. 2(a) (not shown).