Patent GB-863591-A (GB)
Title: Voltage divider of high resolving power
IPC: G06G7/163
Filed: 1958-07-15
Abstract: 863,591. Resistance networks. SVENSKA AKTIEBOLAGET GASACCUMULATOR. July 15, 1958 [July 22, 1957; Feb. 21, 1958], No. 22621/58. Class 40(8) [Also in Group XXXVI] An adjustable circuit for providing an output voltage which is proportional to the "setting", i.e. the ratio between the open-circuit output voltage and the voltage of the source, consists of a combination of three-terminal voltage dividers, Fig. 1, each having an output impedance which is independent of its setting. The voltage divider consists of three impedances A, B, C connected in Y-formation to a current source (A.C. or D.C.) of constant open circuit voltage E and constant resistance R 0 . The open circuit output voltage of the divider is U 0  and the setting of the divider is defined as x = U 0 /E. It is shown in the Specification that, for a constant load R 1 , proportionality between the output voltage U and the setting x is acheived if R = x(R o +r a )+rc=const. where and is the output resistance of the equivalent two-terminal circuit of Fig. 2. This condition can be met for a number of different relationships between r a , r b , r c  depending upon which are held constant. In particular, it is shown that for R 0  = O and r c  = const. the relationship 1/r a  + 1/r b  = 1/(R + r c ) = const. must hold. The conditions for constant input impedance for a finite R 0  are also discussed. Fig. 6 shows a number of voltage dividers (R 0  = O) connected in parallel. The dividers are all matched to the resistance R 0  = O of the source. The dividers have settings X 1 , X 2  ... X n  and output resistances R 1 , R 2  ... R n . It is proved in the Specification that the output resistance R of the composite circuit is constant and that the setting is x = Uo/ E  = X 1 <SP>R</SP>/R1 + x 2  <SP>R</SP>/R 2  + ... X n <SP>R</SP>/Rn. The circuit thus provides an adding voltage divider. Fig. 7 shows a number of dividers connected in cascade, each divider having a constant input resistance R 0 , R 1  ... R n-1 , the output resistance of the source being R 0 . It is shown that the overall setting is x = x 1  x 2  ... X n  so that the circuit is a multiplying voltage divider. Fig. 8 shows a combination of parallel and cascade-connected voltage dividers all of output resistance R and all matched to source of output resistance R 0  = R. It can be shown that the overall setting x of the composite divider is related to the settings of the individual dividers by If the load is R 1 , the voltage across it is U = XER 1 /(R + R 1 ). In the adding network of Fig. 9, the individual dividers have an output resistance of R<SP>1</SP> and resistances 9R<SP>1</SP>, 99R<SP>1</SP>, 999R<SP>1</SP> are connected in series with the outputs of the last three units giving an overall setting x = (x 1  + 0.1x 2  + 0.01x 3  + 0.001 x 4 )/1,111. Resistances 99R<SP>1</SP> and 999R<SP>1</SP> may become impracticably large. In the adding network of Fig. 10, this difficulty is avoided by connecting the third unit in cascade with a unit having a fixed setting of 0.1 and the fourth stage in cascade with two such units. No output resistance need then be greater than 9R<SP>1</SP>. The setting is given by replacing the denominator in the last equation above by 1.3.