GB1352387A - System for adjusting the value of a resistance to a predetermined value - Google Patents

Abstract

1352387 Resistors COMMISSARIAT A L' ENERGIE ATOMIQUE 26 May 1971 [26 May 1970 14 May 1971] 17300/71 Heading HIS A system for adjusting the value R of a resistance to within a predetermined limit of a value Ro by passing a series of power pulses of consecutively increasing power through the resistance to cause oxidation of the material thereof comprises at least two read-in circuits, a read-in circuit 2 for the value Ro and a read-in circuit 4 for the accuracy with which R is required to be adjusted to Ro, i.e. within 10%, 1% or 0À1%; a comparator b, for comparing the values of R and Ro, to which the circuits 2, 4 are connected and having two inputs one of which has two terminals 8, 10 across which the resistance to be trimmed can be connected; a store and control circuit 12 connected to the comparator output and which determines the power of the first pulse and the power increment of the consecutive pulses; a generator 14 producing the pulses connected to the store and control unit output and having output terminals 16, 18 across which the resistance to be trimmed can be connected, the generator having a clock circuit 20 connected to it for the purpose of controlling the repetition frequency and the average width of the pulses. The specification describes two embodiments of the system in detail. In the first (Figs. 2 and 3, not shown) a series of constant width and repetition frequency pulses are supplied to the resistance, each pulse being a constant incremental voltage greater in height than the previous pulse, the initial pulse voltage and the incremental voltages being determined from the value of Ro and the initial value of R, until R is within 10% of Ro as determined by a unit of the comparator. If 10% accuracy is required the process terminates but if 1% accuracy is required a new incremental voltage is calculated and the process continues until 1% accuracy is achieved. The process is then repeated if 0À1% accuracy is required. If at any time the value of R is above Ro by greater than the required accuracy, the resistor is rejected. In the second embodiment (Figs. 4, 5 and 6, not shown) the repetition frequency of the pulses is varied in addition to the pulse height. A series of increasing magnitude pulses, starting from zero, are fed through the resistance until the resistance value is within a given percentage of Ro, e.g. 80%. The pulse height then remains constant but the pulse frequency is decreased in increments for a fixed period of t 0 (Fig. 4, not shown). If after time t 0 the value of R is not within the required limits of Ro, the amplitude of the pulses with decreasing frequency is increased, the increments being smaller than in the first stage, until the required resistance value is obtained.