| 摘要 |
<p>MA9-85-007 EDGE DETECTION USING DUAL TRANS-IMPEDANCE AMPLIFIER A current pulse signal, which is generated by an optical detector, is fed to an input of an edge detector circuit. The current pulse signal is converted into a differentiated voltage pulse signal having a negative going pulse corresponding to a positive going slope of the input signal and a positive going pulse corresponding to the negative going slope of the input waveform. The positive differentiated pulse has a rise amplitude which is larger than its fall amplitude so that its most positive down level has a relatively positive absolute voltage value. Correspondingly, the negative differentiated pulse has a fall amplitude which is greater than its rising amplitude so that its most negative up level is more negative in absolute value than a nominal median zero voltage reference level. The output of the edge detection circuit is connected to a dual threshold comparator having a positive threshold for detecting valid positive differentiated pulses and a negative threshold for detecting valid negative differentiated pulses. Noise components on them most positive down level of the positive differentiated pulse and the most negative up level of the negative differentiated pulse are less likely to exceed the positive and the negative threshold values, respectively, of the comparator. Therefore, the likelihood that a reliable detection of valid positive and negative pulses is enhanced as well as enhancing the noise immunity for background noise in high speed, small amplitude current pulse applications.</p> |
