| 摘要 |
1,135,342. Digital-to-analogue converters. STANDARD TELEPHONES & CABLES Ltd. 10 Feb., 1967, No. 6510/67. Heading G4H. A non-linear digital-to-analogue converter comprises input terminals 1, 2 for the least significant digits and a linear decoder A for producing a proportional voltage V A , input terminals 3, 4, 5 for the most significant digits, a pedestal voltage generator B providing a fourunit pedestal voltage V B when any of the input digits at 3, 4, 5 are " 1 ", a decoding matrix E controlling a multiplier D in accordance with the numerical value of the digits at 3, 4, 5 and a summer C adding the outputs V B and V A and applying the sum to the multiplier. The conversion characteristic comprises seven straight line segments giving an approximation to an exponential curve. The multiplier comprises a series of resistors any one of which may be connected by a switching signal on a corresponding output from the matrix E. The first two resistors are equal so that the first two segments of the characteristic curve have the same slope. Successive segments after the second each have twice the slope of the one before. Instead of using a separate switch and resistor for each digit value, a combinational arrangement may be used. The digits on terminals 3, 4, 5 control the pedestal generator B through OR gate G. An offset signal equal to half a step may be added to output by being applied at a third input to the summer. The code is symmetrical for positive and negative values, the polarity of the signal being indicated by a further digit. |
