| 摘要 |
In a dual slope analogue-to- digital converter an acquisition period formed by a number of fixed intervals determined by the magnitude of the input signal is followed by a conversion period which consequently has a comparatively small variation in length. Thus a problem is overcome since the large range of conversion periods encountered in previous converters is very much reduced. During the acquisition period an integrator 52, 53, 54 integrates an input signal under the control of a comparator 55, 56 and during the conversion period the integrator integrates a reference signal under the control of a comparator 57. The fixed intervals form a geometric progression, allowing a floating point digital output and efficient automatic control of ranges when the converter is used in a component meter. A phase sensitive detector has input corrections, provided via gain- control operational amplifiers, to switch means which connects them alternately with selectable phase to an output amplifier, under control of a reference signal (Fig. 4, not shown). Two different phases, differing by 180 DEG , are used in turn for each measurement, to permit subsequent elimination of D.C. offsets by subtraction. A component meter employing the converter and the phase sensitive detector is also described. <IMAGE> |
