| 摘要 |
A system using digital-to-analog (D/A) conversion techniques where in the AC voltage ouput, as from a sensor (10), for example, is supplied to an AC comparator circuit (14) for comparing its value with the analog output of a D/A transformer circuit (12), the difference signal being used to provide an error signal for use by control logic (15) to control the digital setting of the D/A transformer so that its AC analog output is equal to the sensor AC voltage ouput. The digital setting represents the sensor output in digital form, the most significant bits thereof being determined by a successive approximation technique using finite integration and the least significant bits thereof being determined using dual slope integration. During the dual slope integration process, the comparator circuit uses a specially designed A-C feedback amplifier-filter circuit (23) which reduces the harmonics of the AC operating signal and a specially designed phase sensitive detector (24) which significantly further reduces undesirable third harmonics in particular, as well as higher odd harmonics. |
