The LF198/LF298/LF398 are monolithic sample-and-hold circuits that utilize BI-FET technology to obtain ultra-high 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 adjustment is accomplished with a single pin, and does not degrade input offset drift. The wide bandwidth allows the LF198 to be included inside the feedback loop of 1 MHz op amps without having stability problems. An input impedance of 1010Ω allows high source impedances to be used without degrading accuracy. 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 1μF 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 guarantees no feedthrough from input to output in the hold mode, even for input signals equal to the supply voltages.
