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ADCMP604 Folha de dados(PDF) 11 Page - Analog Devices |
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ADCMP604 Folha de dados(HTML) 11 Page - Analog Devices |
11 / 16 page ADCMP604/ADCMP605 Rev. 0 | Page 11 of 16 The ADCMP604 and ADCMP605 dispersion is typically < 1.6 ns as the overdrive varies from 10 mV to 125 mV. This specification applies to both positive and negative signals because each the ADCMP604 and ADCMP605 have substantially equal delays for positive-going and negative-going inputs and very low output skews. Q/Q OUTPUT INPUT VOLTAGE 500mV OVERDRIVE 10mV OVERDRIVE DISPERSION VN ± VOS Figure 17. Propagation Delay—Overdrive Dispersion Q/Q OUTPUT INPUT VOLTAGE 10V/ns 1V/ns DISPERSION VN ± VOS Figure 18. Propagation Delay—Slew Rate Dispersion COMPARATOR HYSTERESIS The addition of hysteresis to a comparator is often desirable in a noisy environment, or when the differential input amplitudes are relatively small or slow moving. The transfer function for a comparator with Hysteresis is shown in Figure 19. As the input voltage approaches the threshold (0.0 V, in this example) from below the threshold region in a positive direction, the comparator switches from low to high when the input crosses +VH/2. The new switching threshold becomes −VH/2. The comparator remains in the high state until the threshold, −VH/2, is crossed from below the threshold region in a negative direction. In this manner, noise or feedback output signals centered on 0.0 V input cannot cause the comparator to switch states unless it exceeds the region bounded by ±VH/2. OUTPUT INPUT 0 VOL VOH +VH 2 –VH 2 Figure 19. Comparator Hysteresis Transfer Function The customary technique for introducing hysteresis into a comparator uses positive feedback from the output back to the input. One limitation of this approach is that the amount of hysteresis varies with the output logic levels, resulting in hysteresis that is not symmetric about the threshold. The external feedback network can also introduce significant parasitics that reduce high speed performance and induce oscillation in some cases. The ADCMP605 comparator offers a programmable hysteresis feature that significantly improves accuracy and stability. Connecting an external pull-down resistor or a current source from the LE/HYS pin to GND, varies the amount of hysteresis in a predictable and stable manner. Leaving the LE/HYS pin disconnected or driving it high removes hysteresis. The maximum hysteresis that can be applied using this pin is approximately 160 mV. Figure 20 illustrates the amount of hysteresis applied as a function of external resistor value. Figure 11 illustrates hysteresis as a function of current. The hysteresis control pin appears as a 1.25 V bias voltage seen through a series resistance of 7 kΩ ± 20% throughout the hysteresis control range. The advantages of applying hysteresis in this manner are improved accuracy, improved stability, reduced component count, and maximum versatility. An external bypass capacitor is not recommended on the HYS pin because it would likely degrade the jitter performance of the device and impair the latch function. As described in the Using/Disabling the Latch Feature section, hysteresis control need not compromise the latch function. |
Nº de peça semelhante - ADCMP604 |
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Descrição semelhante - ADCMP604 |
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