The LF298 and LFx98x devices are monolithic sample-and-hold circuits that use BI-FET
technology to obtain ultrahigh DC accuracy with fast acquisition of signal and low droop rate.
Operating as a unity-gain follower, DC gain accuracy is 0.002% typical and acquisition time is as
low as 6 µs to 0.01%. A bipolar input stage is used to achieve low offset voltage and wide
bandwidth. Input offset adjust is accomplished with a single pin and does not degrade input offset
drift. The wide bandwidth allows the LF198-N to be included inside the feedback loop of 1-MHz
operational amplifiers without having stability problems. Input impedance of
1010 Ω allows high-source impedances to be used without degrading
P-channel junction FETs are combined with bipolar devices in the output amplifier to give
droop rates as low as 5 mV/min with a 1-µF hold capacitor. The JFETs have much lower noise than MOS
devices used in previous designs and do not exhibit high temperature instabilities. The overall
design ensures no feedthrough from input to output in the hold mode, even for input signals equal
to the supply voltages.
Logic inputs on the LF198-N are fully differential with low input current, allowing for
direct connection to TTL, PMOS, and CMOS. Differential threshold is
1.4 V. The LF198-N will operate from ±5-V to ±18-V supplies.
An A version is available with tightened electrical specifications.
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