Upgrading Popular Analog Devices OP-Amps with Ultra-Low Noise JFET Front Ends

Many widely used ADI op-amps are excellent building blocks-but pairing them with a discrete JFET input stage can unlock lower noise, higher input impedance, and more design flexibility, especially for high-Z sensors and precision analog front ends.

Where discrete JFETs shine: 

• Reduce input current noise and 1/f noise

• Improve performance with high-impedance sources

• Allow custom gain, bandwidth, and linearity tuning

• Enable better thermal tracking and matching

Designers are increasingly using discrete JFET front ends ahead of precision or high-speed op-amps to outperform integrated FET-input solutions—especially in instrumentation, audio, and low-frequency sensor applications.

🔄 Op-Amp Upgrade Paths: From Monolithic to Discrete JFET Front Ends

Looking to improve noise, drift, or flexibility in common Analog Devices op-amp designs? Below are suggested discrete JFET upgrade paths using Linear Systems devices — and why designers make the switch.

• OP27 (Precision BJT, low drift) → Upgrade: LSK389 + ADA4522 → Benefit: Lower current noise with customizable gain

• OP07 (Low offset, low cost) → Upgrade: LSK170 + low-noise op-amp → Benefit: Higher input impedance and lower bias current

• AD8610 (FET-input, low noise) → Upgrade: LSK170 + OPA627 → Benefit: ~7× lower noise and a lower 1/f noise corner

• AD8620 (Dual AD8610) → Upgrade: LSK489 + dual precision amplifier → Benefit: Lower drift with increased design flexibility

• AD825 (High-speed instrumentation amp) → Upgrade: LSK170 + fast op-amp → Benefit: Lower noise and fully customizable gain stages

• AD829 (High-speed, audio) → Upgrade: LSK170 + audio-grade op-amp → Benefit: Lower distortion and improved headroom

• AD620 (Instrumentation amp for sensors) → Upgrade: LSK389 + discrete differential amplifier → Benefit: Better matching and lower offset drift

• AD8237 (Low-power INA) → Upgrade: LSK170 + low-bias op-amp → Benefit: Improved low-frequency performance

• ADA4627-1 (FET-input, high voltage) → Upgrade: LSK170 + ADA4898-1 → Benefit: Lower 1/f noise and more flexible input tuning

• ADA4898-1 (Ultra-low distortion) → Upgrade: LSK170 + discrete gain stage → Benefit: Custom linearity with reduced 1/f noise

 🔊 Low-Noise Op-Amp Alternatives Using Discrete JFET Front Ends

For designs where noise performance is critical, many engineers move beyond monolithic op-amps and use discrete JFET input stages for better matching, lower bias current, and improved low-frequency behavior.

Below are common ADI op-amps, their noise levels, and suggested JFET-based upgrade paths:

• AD797 (0.9 nV/√Hz, BJT) → Upgrade: LSK389 + ADA4522 → Benefit: Matched JFET input ideal for high-impedance sources

• ADA4898-1 (1.0 nV/√Hz, BJT) → Upgrade: LSK170 + ADA4898-1 → Benefit: Same op-amp with improved front-end performance

• AD8597 (1.1 nV/√Hz, BJT) → Upgrade: LSK170 + audio-grade op-amp → Benefit: Lower bias current with flexible layout options

• AD8599 (Dual version) → Upgrade: LSK489 + precision amplifier → Benefit: Monolithic dual JFET input stage with improved matching

• AD8429 (Instrumentation amplifier) → Upgrade: LSK389 + discrete differential amplifier → Benefit: Better matching and lower drift for sensor interfaces

• ADA4627-1 (3.3 nV/√Hz, JFET) → Upgrade: LSK170 + ADA4898-1 → Benefit: Lower input noise and reduced 1/f noise corner

• AD8610 (6.0 nV/√Hz, JFET) → Upgrade: LSK170 → Benefit: ~7× lower voltage noise

• AD8620 (6.0 nV/√Hz, dual JFET) → Upgrade: LSK489 → Benefit: Improved noise, drift, and channel-to-channel matching

• AD743 (2.9 nV/√Hz, JFET) → Upgrade: LSK389 → Benefit: Monolithic dual JFET replacement with better SNR

• AD745 / AD746 (3.5 nV/√Hz, JFET) → Upgrade: LSK170 / LSK489 → Benefit: Higher input impedance with lower noise

• AD820 (~7.5 nV/√Hz, JFET) → Upgrade: LSK170 → Benefit: Significant noise reduction

 Summary Recommendation:

• For precision designs, LSK389 offers a monolithic dual solution with unmatched thermal tracking and <1 nV/√Hz noise.

• For cost-sensitive upgrades, LSK170 provides low noise and high impedance in a single-channel format.

• For drop-in dual replacements, LSK489 offers matched performance with reduced layout complexity.

Use our JFETs to build lower-noise, custom-tuned, and sensor-friendly analog front ends that outperform ADI’s integrated FET-input amplifiers.

Have you tried a discrete JFET front end in your designs?