| 摘要 |
1510322 Digital-to-analogue conversion DEUTSCHE TEXACO AG 20 June 1975 [22 June 1974] 26402/75 Heading H3H Data digitally stored in the form of mantissa A and exponent E to integer base B is converted to analogue signals, compression being obtained by varying the reference voltage V ref of a digital to analogue converter 14, the reference voltage being derived by sampling at a time determined by the data a sawtooth reference voltage that rises in each cycle from an initial value to a final value B times the initial value. In Fig. 1, coarse and fine compression is employed: for coarse, the mantissa is shifted in register 13 according to the difference between E and the state of a counter 20; for fine, V ref is varied by algebraic summation at 16 of the averaged output of the digital to analogue converter, the value of V ref used for the previous conversion cycle and a ramp voltage which may be linear or exponential, to define a time at which the reference sawtooth, which is exponential, is to be sampled. There may be several sawtooth cycles for each conversion cycle, the actual reference cycle sampled being used to control the counter 20 in the coarse loop. |
