AD817OFFSET NULLING Measuring the rapid settling time of AD817 (45 ns to 0.1% and The input offset voltage of the AD817 is inherently very low. 70 ns to 0.01%–10 V step) requires applying an input pulse with However, if additional nulling is required, the circuit shown in a very fast edge and an extremely flat top. With the AD817 con- Figure 32 can be used. The null range of the AD817 in this con- figured in a gain of –1, a clamped false summing junction re- figuration is ± 15 mV. sponds when the output error is within the sum of two diode voltages (ª1 volt). The signal is then amplified 20 times by a AD817 SETTLING TIME clamped amplifier whose output is connected directly to a sam- Settling time is comprised primarily of two regions. The first is pling oscilloscope. Figures 33 and 34 show the settling time of the slew time in which the amplifier is overdriven, where the the AD817, with a 10 volt step applied. output voltage rate of change is at its maximum. The second is the linear time period required for the amplifier to settle to 0 within a specified percent of the final value. –2–410–68–86–10OUTPUT SWING – Volts420.2000.15OUTPUT SWING – Volts0.100.050.0500OF FINAL VALUE0.050.05SETTLING TIME TO %0.100501001502002503003504000.15OF FINAL VALUE 0.20 Figure 34. Settling Time in ns 0 V to –10 V SETTLING TIME TO %050100150200250300350400 Figure 33. Settling Time in ns 0 V to +10 V 2 × HP2835ERROR AMPLIFIER1M Ω 15pFVOUTPUT × 10ERROR53100 Ω 2 × HP2835AD829SETTLING6OUTPUT0.47 µ F42SHORT, DIRECT7CONNECTION TO0.01 µ FTEKTRONIX TYPE 114020.01 µ FOSCILLOSCOPE PREAMPERRORINPUT SECTION0.47 µ FSIGNALOUTPUT–V+VSS100 Ω 1.9k Ω 0 TO ± 10VNOTE:POWERUSE CIRCUIT BOARDFALSESUPPLYEI&SWITH GROUND PLANENULLDL1A05GMSUMMINGADJUSTMERCURY RELAYNODE7, 81k Ω 100 Ω 500 Ω 1k Ω 250 Ω 13DEVICETTL LEVELCOAX5–18pFUNDERSIGNALTEKTRONIX P62011, 14CABLE500 Ω TESTGENERATORFET PROBE TO50Hz2TEKTRONIX TYPEOUTPUT50 Ω AD81711402610pFOSCILLOSCOPE37SCOPE PROBEPREAMP INPUT4CAPACITANCESECTION2.2DIGITAL µ F0.01 µ FGROUND2.2 µ F0.01 µ F+VSANALOG GROUND–VS Figure 35. Settling Time Test Circuit –10– REV. B