| 摘要 |
A square pulse wave is frequency modulated (FM) by an input analog voltage that represents a physiological parameter such as an electrocardiograph waveform. A binary counter is initiated for counting a predetermined integral number, such as four, FM periods for each FM wave sampling interval. A counter/timer counts high rate clock pulses during the interval and stops when the predetermined number of FM periods is counted, thereby producing a count that is proportional to the time per FM period or cycle. The reciprocal of time is calculated to produce a digital number that is proportional to frequency and, hence, to the instant amplitude of the analog input voltage. The number constitutes address to a look-up table storing digital words that correspond in value to dc voltages.
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