LF398M/NOPB | Texas Instruments

Monolithic Sample-and-Hold Circuits, LF398M/NOPB, Texas Instruments

The LF398M/NOPB device is a monolithic sample-and-hold circuit 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 LFx98x to be included inside the feedback loop of 1-MHz operational amplifier without having stability problem. Input impedance of 1010 Ω allows high-source impedance to be used without degrading accuracy. A P-channel junction FET is combined with a bipolar device in the output amplifier to give a droop rate as low as 5 mV/min with a 1-μF hold capacitor. The JFET has much lower noise than a MOS device used in a previous design and does not exhibit high temperature instability. The overall design ensures no feedthrough from input to output in the hold mode, even for an input signal equal to the supply voltage. A logic input on the LFx98x is fully differential with low input current, allowing for direct connection to TTL, PMOS, and CMOS. Differential threshold is 1.4 V. The LFx98x will operate from a ±5-V to ±18-V supply.

Features

• Less than 10-μs Acquisition Time
• Low Input Offset
• Low Output Noise in Hold Mode
• Input Characteristics Do Not Change During Hold Mode
• High Supply Rejection Ratio in Sample or Hold
• Wide Bandwidth

Applications

• Ramp Generators With Variable Reset Level
• Integrators With Programmable Reset Level
• Synchronous Correlators
• 2-Channel Switches
• DC and AC Zeroing
• Staircase Generators