Datasheet ADCMP567 (Analog Devices) - 10

link to page 10 link to page 10 link to page 11 link to page 11 link to page 10
ADCMP567 Data Sheet
as the variation in propagation delay as the input overdrive
–VH +VH 2 2
conditions are changed (see Figure 4). For the ADCMP567,
0V
overdrive dispersion is typically 35 ps as the overdrive is
INPUT
changed from 100 mV to 1 V. This specification applies for both
1
positive and negative overdrive since the ADCMP567 has equal delays for positive and negative going inputs. The 35 ps propagation delay overdrive dispersion of the ADCMP567 offers considerable improvement of the 100 ps dispersion of other similar series comparators.
1.5V OVERDRIVE 0 INPUT VOLTAGE OUTPUT 20mV OVERDRIVE VREF ± VOS 03633-0-005
Figure 5. Comparator Hysteresis Transfer Function
60 DISPERSION Q OUTPUT 50 03633-0-004 40
Figure 4. Propagation Delay Dispersion
V) m COMPARATOR HYSTERESIS 30 ESIS (
The addition of hysteresis to a comparator is often useful in a noisy environment or where it is not desirable for the com-
YSTER 20 H
parator to toggle between states when the input signal is at the switching threshold. The transfer function for a comparator
10
with hysteresis is shown in Figure 5. If the input voltage approaches the threshold from the negative direction, the
0 –25 –20 –15 –10 –5 0 5
comparator will switch from a 0 to a 1 when the input crosses 
LATCH = LE – LEB (mV)
03632-0-006 +VH/2. The new switching threshold becomes −VH/2. The Figure 6. Comparator Hysteresis Transfer Function comparator will remain in a 1 state until the threshold −VH/2 is Using Latch Enable Input crossed coming from the positive direction. In this manner,
MINIMUM INPUT SLEW RATE REQUIREMENT
noise centered on 0 V input will not cause the comparator to switch states unless it exceeds the region bounded by ±V As for all high speed comparators, a minimum slew rate must H/2. be met to ensure that the device does not oscillate when the Positive feedback from the output to the input is often used to input crosses the threshold. This oscillation is due in part to the produce hysteresis in a comparator (see Figure 9). The major high input bandwidth of the comparator and the parasitics of problem with this approach is that the amount of hysteresis the package. Analog Devices recommends a slew rate of 5 V/μs varies with the output logic levels, resulting in a hysteresis that or faster to ensure a clean output transition. If slew rates less is not symmetrical around zero. than 5 V/μs are used, then hysteresis should be added to reduce Another method to implement hysteresis is generated by the oscillation. introducing a differential voltage between LATCH ENABLE and LATCH ENABLE inputs (see Figure 10). Hysteresis generated in this manner is independent of output swing and is symmetrical around zero. The variation of hysteresis with input voltage is shown in Figure 6. Rev. A | Page 10 of 14 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL CONSIDERATIONS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TIMING INFORMATION APPLICATIONS INFORMATION CLOCK TIMING RECOVERY OPTIMIZING HIGH SPEED PERFORMANCE COMPARATOR PROPAGATION DELAY DISPERSION COMPARATOR HYSTERESIS MINIMUM INPUT SLEW RATE REQUIREMENT TYPICAL APPLICATION CIRCUITS TYPICAL PERFORMANCE CHARACTERISTICS OUTLINE DIMENSIONS ORDERING GUIDE