| 摘要 |
A digital signal processing apparatus for operating upon analog signals having wide dynamic and frequency ranges is described. The invention includes a digital section and an analog section, the digital section providing digital words representative of analog signals to be transmitted, and receiving digital representations of analog signal received from the test subject, and processing said digital representations. The analog section transforms the digital representations of the signals to be transmitted into analog form and applies them to the test subject by way of a balanced output driver. The analog section includes a receiving section which receives analog signals from the test subject and transforms the analog signals into digital representations thereof. The digital section also provides control information to the analog section. The data and control information being communicated between the analog and digital sections are transferred by way of optical isolators. Further, the analog section is powered by a floating power supply. As such the analog section presents an input and an output port to the test subject which are transformer-like; i.e. floating and balanced. Further disclosed is a method for frequency measurement which determines and operates upon the time interval which corresponds to the integral number of half cycles in the incoming waveform. To provide enchanced noise rejection in the frequency measurement, a nonzero threshold level is employed to validate each half cycle in the waveform. The results are then displayed in accordance with a method which permits quick response of the display to large variations in the measurements, and slower response to small variations in the measurements.
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