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Elegant analog design often comes down to simplicity. This 4–20 mA current-sense circuit shows how a single JFET can do the job with minimal parts. "Sometimes the simplest solution is the best. Using a single N channel JFET as a current sink, a 4-20mA instrument monitor loop can be read with a minimum of components. A 2N4392 diverts a current of 4mA until the load circuit voltage exceeds the Zener threshold where the remaining current up to 20 mA is diverted giving a linear indication from 4-20mA. Given that the two-wire polarity is known,  the Bridge rectifier can be eliminated, further simplifying the circuit. The bridge simply makes it fool proof...." - Kirkwood Rough

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?

Understanding Noise Performance in Precision Design As precision analog systems continue to push the limits of sensitivity, stability, and signal integrity, noise performance is no longer a “nice to have” — it’s a design requirement . Engineers must prioritize noise performance to ensure that their designs meet the necessary standards for reliability and accuracy. At Linear Integrated Systems, ultra-low-noise JFETs have long played a critical role in applications where engineers can’t afford variability or guesswork. From medical sensing and instrumentation to radar, defense, and professional audio, designers increasingly need components with predictable, repeatable performance , not just typical or sampled specifications. The Importance of 100% Noise Testing That’s why we continue to spotlight our approach to 100% noise testing across our ultra-low-noise JFET portfolio, including the LSK170 single JFET and LSK389 monolithic dual JFET . Every device is verified before shipment — helping engineers reduce design risk, shorten validation cycles, and improve long-term system stability. Applications of Ultra-Low-Noise JFETs Ultra-low-noise JFETs are used in various demanding applications. These include: Medical Devices : In medical sensing, precision is crucial. Noise can significantly impact the accuracy of readings. Radar Systems : Noise performance is vital for reliable detection and tracking. Professional Audio : In audio applications, noise can degrade sound quality. Engineers must consider these factors when selecting components for their designs. Why Full Noise Verification is Critical In our latest press release, we share: Why full noise verification is becoming more critical as systems grow more sensitive. How monolithic dual JFETs improve matching and thermal stability. Where ultra-low-noise JFETs are being used across today’s most demanding applications. Enhancing Design Reliability By focusing on verified noise performance, engineers can enhance the reliability of their designs. This is especially important in fields where performance is non-negotiable. 👉 Read the full press release here: https://www.prnewswire.com/news-releases/linear-integrated-systems-spotlights-industrys-only-100-noise-tested-ultra-low-noise-jfets-302643454.html Conclusion In conclusion, verified noise performance is essential in precision design. As systems become increasingly sensitive, the need for reliable, low-noise components will only grow. By prioritizing noise testing, engineers can ensure their designs meet the highest standards of performance and reliability. ---wix---

Community Design Spotlight 🔍 WSF Amplifier “The Watt Sucking Fireball  amplifier illustrates a wide use range of Linear Systems  JFETs and matched bipolar transistors. It has an all JFET front end using a (Differential-Cascode-Transimpedance)™ amp driving a resistor loaded differential current to voltage gate driver; a lot to say in one sentence. Though simple in overall design concept, the goal of this design was to prove out an all N-channel JFET amplifier having almost no intermodulation distortion using a linear low loop gain signal path and minimal feedback. The output JFETs are vertical Power JFETs made by Sony in the 1970s. The vertical C7 driver FETs were my own fabrication in 1994. But that’s a whole other story. Though the debate rages on, audio is always AC so capacitors selected well are valid, and Nelson Pass said so. This input diff stage has capacitor coupled sources, as does the output stage driver. Independent current sources set preamp quiescent voltage matching. Independent current sources make output zeroing simple via a differential current steering integrator to balance gate drive current sources. Output JFETs are negatively biased gate to source and thus balanced to zero the output DC voltage. Linear Systems  single & dual JFETs and Matched bipolars are effectively used in the entire bias management system.  The DCT  (Differential Cascode Transimpedance)™ preamp was invented for the Linear Systems  2009 Burning-Amp Festival Demo. Following founder John Hall, I have been designing discrete transistor and JFET circuitry with Linear Systems parts since their first year of founding in 1987, and before that, Micropower Systems , much of it in Semiconductor fabrication machine instrumentation. Discrete Music amplifier design is now a 60-year continued preoccupation.” - J Kirkwood H Rough

For decades, Junction Field-Effect Transistors (JFETs) have quietly powered the most sensitive electronic systems on Earth. Even as integrated circuits become more advanced, the discrete JFET remains unmatched when ultra-low noise, high impedance, and precision analog performance are required. At Linear Systems, delivering world-class discrete JFETs is our core specialty — with modern, U.S.-manufactured devices that outperform discontinued legacy parts and offer superior noise, gain, and matching characteristics. The Unique Properties Behind the JFET Advantage Ultra-High Input Impedance With extremely high resistance and low capacitance, Linear Systems JFETs connect directly to high-impedance sensors without loading or signal loss. Ultra-Low Noise & Low 1/f Noise Our LSBF862, LSK389, LSJ74, and LSK170 families deliver noise levels that integrated devices simply cannot match — critical for microvolt-level measurement. High Gain & Low Distortion Essential for high-fidelity audio, scientific instruments, and precision analog front ends. Low Voltage Operation Ideal for low-power and battery-based systems where accuracy cannot be compromised. Where Linear Systems JFETs Power Modern Designs 🎧 1. High-Fidelity Audio & Musical Instrument Preamps Low distortion, smooth clipping, and consistent device-to-device matching make our JFETs the preferred choice for boutique and professional audio designers. 🔬 2. Scientific & Precision Electronic Measurement JFETs form the front end of oscilloscopes, DMMs, capacitance meters, photon detectors, lab instruments, and medical electronics. 📡 3. Sensor-Driven Systems & IoT From smart cities to wearable tech, JFET preamplifiers enable accurate sensing of acceleration, pressure, heat, light, sound, and radiation. ❤️ 4. Medical & Fitness Wearables JFETs deliver the ultra-low flicker noise needed for ECG, PPG, and next-generation optical biosensing. Why Discrete JFETs Outperform Integrated Versions JFETs degrade when forced into tiny geometries: Noise performance worsens Matching becomes inconsistent Cost increases Input capacitance rises For ultra-low-noise, low-frequency, microvolt-level signals, only a discrete JFET can deliver the required performance . This is precisely why engineers continue to rely on Linear Systems’ precision-engineered devices. The Linear Systems Difference We manufacture one of the world’s most advanced portfolios of discrete JFETs, including: 🔹 LSBF862 — Industry’s best BF862 replacement Superior noise, improved consistency, and long-term availability. 🔹 LSK389 / LSJ689 — Ultra-low noise dual JFETs Matched pairs ideal for instrumentation and high-end audio. 🔹 LSK170 / LSJ74 — High-performance single JFETs Used globally in premium audio and precision sensors. 🔹 Complementary product families DMOS analog switches, VCRs, CRDs, MOSFETs, and low-leakage diodes for complete analog front-end design. Engineers choose Linear Systems for: Unmatched noise and gain performance Tight process control and device matching Long-term manufacturing stability U.S.-based production and supply chain security Drop-in replacements for legacy JFETs Conclusion: The Future of Analog Still Runs on JFETs As systems become more sensor-driven and measurement precision becomes more demanding, JFETs remain irreplaceable . Linear Systems is proud to support the engineers building tomorrow’s audio systems, medical devices, scientific instruments, and IoT technologies. 🔗 Explore Linear Systems JFET Products https://www.linearsystems.com/jfets 🔗 LSBF862 Product Page https://www.linearsystems.com/jfetamplifierssingles/lsbf862 🔗 Request Samples, Pricing, or Technical Support https://www.linearsystems.com/about-2

When NXP discontinued the BF862, engineers around the world were left searching for a true low-noise replacement that preserved performance, ensured long-term supply continuity, and avoided expensive redesigns. Linear Integrated Systems is proud to introduce the LSBF862 , a precision N-channel JFET engineered not just to replace the BF862 — but to outperform it  across noise, breakdown voltage, and customizability. 👉 Read the full press release here: https://www.prnewswire.com/news-releases/linear-integrated-systems-introduces-lsbf862-superior-lower-noise-n-channel-jfet-replacement-for-discontinued-nxp-bf862-302630759.html?tc=eml_cleartime Why the LSBF862 Matters The discontinuation of the NXP BF862 created major challenges for designers working in audio, instrumentation, medical, sensing, and underwater acoustic applications. Many teams were forced into last-minute lifetime buys or faced the costly task of requalifying new components. The LSBF862 eliminates those risks — delivering improved performance and guaranteed long-term availability for your legacy and next-generation designs. Key Performance Advantages Ultra-Low Noise 4.0 nV/√Hz @ 10 Hz (Max): Perfect for ultra-low-signal environments, high-sensitivity amplifiers, and precision front-ends. Higher Breakdown Voltage Minimum BVGSS = 40V: Supports robust, stable operation in demanding analog circuits. High Gain & Low Capacitance Yfs = 45mS (typ) Ciss = 10pF (typ): Ideal for preserving signal fidelity and maximizing bandwidth. Radiation-Tolerant JFET Process Provides reliable behavior in harsh and mission-critical environments. Special Testing Options Available for Vgs(off)  and IDSS Supported in SOT-23 (3L)  and bare-die  formats. Perfect for engineers who require tighter specifications or matched performance. Where the LSBF862 Excels This device is purpose-built for high-precision analog applications, including: Low-Noise Amplifiers (LNAs) Discrete op amp designs Photo-diode and TIA stages High-impedance probes Acoustic and hydrophone preamps Battery-powered instrumentation Ultra-sensitive sensors Audio front-ends Medical electronics Test & measurement systems If your design demands low noise, stability, and long-term sourcing, the LSBF862 belongs in your evaluation pipeline. Pricing & Availability USD $1.35 each (1,000+ piece pricing) Samples and full production quantities available now Delivery:  Factory stock to 8 weeks Available directly through Linear Integrated Systems and our authorized distributors. 👉 REQUEST SAMPLES, DATASHEETS OR VOLUME PRICING HERE! A Word From Our CEO “The LSBF862 gives design engineers and procurement departments higher performance and long-term supply continuity.”— Cindy Johnson, CEO, Linear Integrated Systems Learn More Explore the full details in our official press release here:🔗 https://www.prnewswire.com/news-releases/linear-integrated-systems-introduces-lsbf862-superior-lower-noise-n-channel-jfet-replacement-for-discontinued-nxp-bf862-302630759.html?tc=eml_cleartime

When you’re trying to detect tiny signals at the bottom of the ocean, the front end of your signal chain can make or break the entire system. Towed arrays, hull-mounted sonars, and underwater acoustic modems all share one unforgiving requirement: you don’t get a second chance at the data . Once noise, drift, or mismatch pollutes a hydrophone’s output, there’s no DSP magic that can fully restore what’s been lost. That’s why so many designers working with hydrophones and piezoelectric transducers are turning to the LSK389 , a monolithic dual N-channel JFET engineered specifically for ultra-low-noise, high-integrity signal capture . Why the Front-End JFET Matters So Much Underwater Hydrophones and underwater acoustic sensors often deal with: Extremely low signal levels  from distant or low-amplitude sources Long cable runs  in noisy, harsh EMI environments Wide temperature swings , especially in deep or varying thermocline conditions High source impedance , which magnifies the impact of input noise and leakage In these systems, the very first active device — typically a JFET or JFET-input stage — sets the noise floor and stability for everything downstream. A poorly matched or noisy device at the front end can lead to: Elevated system noise floor Channel-to-channel mismatch across arrays DC offset drift that complicates calibration and beamforming Reduced detection range and degraded SNR This is exactly the class of problem the LSK389  is designed to solve. The LSK389: Built for Hydrophones & Acoustic Arrays The LSK389  is a monolithic dual JFET that delivers: Ultra-low thermal noise: Ideal for very low-level signals at the hydrophone output, helping extend detection range and preserve fine detail. Exceptional VGS tracking: Because both JFETs are on the same die, they track closely over temperature and time. This is especially important in differential and balanced front ends  common in towed array systems. Lower offset for cleaner, more stable baselines: Reduced offset makes it easier to calibrate and maintain stable references over long deployments, cutting down on re-trims and compensation complexity. High input impedance for piezoelectric sensors: The LSK389’s very high input impedance allows your hydrophones and transducers to operate as intended, with minimal loading and minimal loss of low-frequency information. Put simply: the LSK389 is designed to capture more of the ocean — and less of your own system noise. Ideal Applications in Underwater Acoustics The LSK389 is a strong fit anywhere low noise, high stability, and tight matching  are required, especially in: Towed array hydrophone preamplifiers Use the LSK389 as the input device in differential or charge amplifier topologies to maximize SNR and maintain consistent performance across many channels. Sonar front ends From passive listening systems to active sonar receive paths, the LSK389 helps ensure that reflections and echoes aren’t masked by front-end noise. Underwater acoustic modems Modems operating in noisy or bandwidth-constrained environments benefit from clean, low-noise analog front ends that preserve constellation integrity and reduce bit error rates. Transducer conditioning modules JFET-based front ends with the LSK389 can be used in compact, sealed modules right at the sensor to minimize cable-induced noise. Design Considerations: Getting the Best from the LSK389 While every design is different, here are a few general tips when using the LSK389 in hydrophone and acoustic applications: Leverage the monolithic dual Use both JFETs in matched configurations (differential pairs, cascoded stages, or balanced inputs) to take full advantage of tight VGS tracking. Pay attention to layout and shielding Even with a low-noise device, poor PCB layout or ground strategy can ruin performance. Keep sensitive nodes short, use solid ground planes, and route noisy digital lines away from the front end. Optimize biasing for your noise and bandwidth targets Bias current affects noise performance. Dial in your operating point for the best trade-off between noise, linearity, and power consumption. Control temperature where possible While the LSK389 is designed for stability, any analog front end benefits from good thermal management, especially in high-density array electronics. Try the LSK389 in Your Next Towed Array or Hydrophone Design If you’re designing: Towed arrays Hull-mounted sonar systems Distributed hydrophone networks Underwater acoustic modems or transducer modules …the LSK389  is an excellent candidate for your front-end JFET. We’re currently making the LSK389 available to evaluate at no cost , so you can see its performance in your own hydrophone or acoustic array design. 📩 Request samples here  and our team will follow up with you to get the right configuration into your lab.

For more than three decades, designers have turned to JFETs for their ability to deliver precision, low-noise performance in sensitive analog circuits. Unlike bipolar junction transistors (BJTs), which operate as current-controlled devices, JFETs function as voltage-controlled current sources , giving designers a unique balance of flexibility, stability, and ultra-high input impedance. Why JFETs Matter JFETs provide giga-ohm-level input impedances and picoamp-level input leakage currents — characteristics that make them ideal for applications demanding high sensitivity and low noise. These traits make them indispensable in instrumentation, sensor interfaces, and high-end audio designs. Key parameters engineers evaluate include: IDSS  (drain-source saturation current) VGS(OFF)  (pinch-off voltage) Gfs  (transconductance) en  (voltage noise density) CISS and CRSS  (input and reverse transfer capacitances) Each of these influences circuit gain, linearity, and noise performance — meaning design engineers often balance one characteristic against another to meet specific performance goals. Matched Dual JFETs for Precision Design When circuit matching and temperature tracking are critical — such as in differential amplifier stages — monolithic dual JFETs  are the best choice. Linear Integrated Systems’ matched pairs like the LSK389, LSK489, and LSJ689  are fabricated on the same chip, ensuring tight parameter tracking and ultra-low noise performance. These devices deliver exceptional common-mode rejection ratio (CMRR)  and minimal offset voltage, making them the preferred choice for low-noise amplifiers, sensor preamps, and precision audio front ends. Applications That Benefit from JFETs JFETs excel in both high-performance and low-power environments, including: Audio:  Microphone and phono preamplifiers for dynamic, ribbon, or electret transducers Instrumentation:  Vibration and piezoelectric sensor amplifiers Scientific and medical:  Photodiode, Geiger tube, or ECG/EKG front-end circuits Low-Power Designs:  Battery or energy-harvesting circuits powered by solar, thermal, or motion energy Beyond Amplification — Switching and Oscillation JFETs aren’t limited to amplification. They can also function as voltage-controlled resistors or switches , as in the LS26VPS , or serve in ultra-low-power oscillator circuits , such as those using the LSK170A . These designs can operate with supply voltages as low as 20 mV, making JFETs viable in applications where every microamp matters. In Summary From high-end audio and RF front ends to precision instrumentation and energy-scarce systems, JFETs remain unmatched for small-signal design flexibility and low-noise performance . Whether configured as amplifiers, oscillators, or variable resistors, Linear Integrated Systems’ JFETs provide the control, precision, and reliability engineers demand. 🔗 Learn more: LSK389 Series Datasheet, LSK489 Series Datasheet, LSJ689 Series Datasheet, Comparing JFETs Application Note

When speed and precision matter, our SD5400CY monolithic quad switch  delivers unmatched performance for Automated Test Equipment (ATE)  and other high-speed analog switching applications. Built on Linear Systems’ proprietary DMOS process , the SD5400CY integrates four individual enhancement-mode MOSFETs  on a common substrate, achieving exceptional channel isolation , low crosstalk (-107 dB) , and ultra-fast switching times  — tON = 1 ns max . Why It Stands Out ⚡ Blazing speed:  1 ns turn-on and 2 ns turn-off 🧩 Quad SPST configuration:  Simplifies complex ATE routing 🔇 Low capacitance:  Only 0.2 pF reverse transfer  minimizes signal distortion 🔒 Zener-protected inputs:  Enhanced reliability under high-voltage conditions 💡 ±10 V analog signal capability  and low rDS(on) (≤ 75 Ω @ 5 V)  for precision analog performance Perfect for High-speed ATE matrix routing Sample-and-hold  circuits Video switching , multiplexers , and DAC deglitchers Pixel-rate signal control  in imaging and sensor applications 🎁 Get your free SD5400 sample kit  now for your next test board. 👉 Request Samples

At Linear Systems, we’ve long been committed to helping designers push the limits of analog performance — especially in low-noise, high-impedance applications such as sensor front-ends, microphone preamps, instrumentation amplifiers and more. That’s why we are proud to present the application note on our dual monolithic JFET, the LSK389.In this article, we’ll walk you through what makes the LSK389 a standout device, how it works in real-world circuits, and how you can integrate it to unlock superior performance in your designs. Why the LSK389 matters The LSK389 is billed as “the industry’s lowest noise Dual N-Channel JFET,” fully noise-tested and guaranteed to meet both low-frequency (1/f) noise and broadband noise specifications. Key specifications include: Input noise of ~1.3 nV/√Hz at 1 kHz (ID = 2 mA) Input noise of ~1.5 nV/√Hz at 10 Hz (ID = 2 mA) Transconductance (gm) ~14 mS at ID = 2 mA Device typical capacitances: CISS ~25 pF, CRSS ~5.5 pF Breakdown voltage ≥ 40 V Four grades based on IDSS (A-D) to give flexibility in biasing and device selection. What this means in practice is that you get a JFET device optimized for ultra-low noise (both wideband and 1/f), excellent matching (because it’s a dual monolithic pair), and high input impedance — making it an ideal front-end building block for very demanding analog systems. Understanding the fundamentals The application note provides a useful refresher of JFET basics: the drain current equation ID=β(VGS−VT)2I_D = \beta (V_{GS} - V_T)^2ID​=β(VGS​−VT​)2 (for VDS > Vt) and how transconductance gm relates to device bias (gm ≈ 2 √(β × ID)). It then dives into the major noise sources in JFETs: Thermal channel noise Gate-current shot noise 1/f noise Generation-recombination noise Impact ionization noise The takeaway: in a well-designed, modern process (such as ours), the first two noise sources can dominate — and by maximizing gm (via sufficient bias current) while minimizing parasitic resistances and capacitances, you can push input-referred noise down. Indeed, for one measured LSK389 device at 2 mA, the thermal noise calculation gives ~0.9 nV/√Hz. Circuit implementation examples The application note gives several practical circuit topologies including: Single-ended amplifier with parallel JFETs to reduce noise by ~3 dB. Differential pair input stage using the LSK389, noting that a differential configuration imposes a ~3 dB noise penalty vs. a single-ended stage (all else equal) because both halves contribute. Cascoded and bootstrapped cascode amplifiers to improve output impedance, reduce Miller effect, and allow high-voltage operation. A very high-performance, ultra-low noise folded-cascode amplifier (with four parallel differential pairs of LSK389 devices) achieving ~0.7 nV/√Hz input-referred noise in a differential amplifier. Also covered: substrate bias considerations (since the dual monolithic pair shares a substrate, and substrate diodes exist between the gates and the substrate). Design tips for optimal use Based on the note and our internal best practice: Bias the LSK389 at ~2–4 mA for a good trade-off of noise vs. power dissipation (note: at 8 mA the device runs hotter, raising noise slightly) When paralleling devices for lower noise, ensure each has its own tail current source (in the case of differential inputs) to avoid instability or bias mismatches. Use low-noise current sources and keep source-degeneration resistors minimal, since they degrade noise performance. Consider cascode configurations if you need higher voltage tolerance or better bandwidth but verify stability via simulation due to potential HF anomalies in bootstrapped/ driven-cascode arrangements. When you have very high-impedance sources (for example, piezoelectric sensors, condenser mics, or GΩ ranges), gate leakage/ current shot noise and substrate diode leakage become increasingly important — so good device matching and low leakage are critical. Why it matters for your system Because we at Linear Systems focus on analog performance, small-signal discrete semiconductors and legacy designs with modern relevance (including switching, modulation and low-noise front-ends), the LSK389 perfectly fits into applications where every nanovolt counts. Whether you’re designing: A phonograph (MM/MC) preamp for an audiophile system A high-impedance sensor preamp for piezoelectric or pyroelectric devices A front-end for a condenser microphone An electrometer or ultra-low current instrumentation amplifier — the LSK389 gives you a strong foundation. Conclusion With the LSK389, you get a dual monolithic matched JFET pair that delivers best-in-class low noise, excellent matching, low capacitance and high transconductance. The application note by renowned analog designer Bob Cordell provides the theory, design examples and tips you need to put that device to work. If you’re designing low-noise analog front-ends, we invite you to download the note and consider the LSK389 in your next iteration. Download the full application note by clicking here Need evaluation samples?  Contact our team — we’re happy to support your prototype and production needs. Call (510) 490-9160 or email support@linearsytems.com .

When designing high-impedance, low-noise front ends—whether for audio preamps, instrumentation nodes, or sensor interfaces—the input stage is everything. The LS844 Dual N-Channel JFET  from Linear Integrated Systems is engineered specifically for these precision applications, offering low noise , low input capacitance , and tight device matching  on a single, monolithic die. This combination allows designers to extract maximum signal fidelity  across a wide range of applications—from high-end audio  to ultra-sensitive sensor readout . What Makes the LS844 Unique? Unlike typical dual JFETs, the LS844 integrates both JFET devices on the same piece of silicon , which ensures: Excellent Vgs matching Superior thermal tracking High common-mode rejection (102 dB CMRR) Consistent, predictable performance across temperature This tight pairing is essential in differential input stages—and is a core reason high-end audio designers choose the LS844. In addition, the LS844 offers: Feature Benefit Low Noise: 2.5 nV/√Hz @ 1 kHz (typ.) Preserves detail in low-level signals Low Input Capacitance (~4 pF) Reduces IMD and improves high-frequency cleanliness Nearly Zero Popcorn Noise Eliminates burst-style distortion artifacts SOT-23-6 (RoHS) Compact, modern, surface-mount friendly Why It Performs Better Than High-Capacitance JFETs In many audio and instrumentation circuits, input capacitance  is the hidden source of distortion—especially when working with high-impedance sources. JFETs with high gate capacitance require additional cascode circuitry  to prevent nonlinear capacitance from producing intermodulation distortion. The LS844 avoids this issue through its very low capacitance , enabling simpler, cleaner designs that preserve clarity across frequency. The LS844 maintains high input impedance even as frequency rises, significantly improving distortion performance in comparison to high-capacitance devices. Ideal Application Areas ✅ High-End Audio Preamplifiers ✅ Microphone Preamps (Dynamic & Condenser) ✅ Phono Preamplifiers (MM / MC) ✅ Sensor & Charge Amplifier Interfaces (Piezo, MEMS, Electret) ✅ Discrete Operational Amplifiers ✅ Low-Level Measurement & Electrometry The LS844 is used anywhere the signal is small, the input impedance must be high, and noise must be preserved—not added. Example: High-Performance Audio Phono Stage The LS844 excels in phono front-ends, where the cartridge impedance interacts directly with input capacitance. Because of its low input capacitance , the LS844 reduces: High-frequency noise rise Cartridge interaction distortion Harmonic and intermodulation artifacts This results in cleaner, more natural analog reproduction —especially noticeable in cymbals, strings, and spatial ambiance. Resources & Links Item Link LS844 Datasheet https://www.linearsystems.com/jfet-amplifiers-duals/ls844-series LS844 Application Note (Detailed Design Guidance) https://www.linearsystems.com/ls844-application-note Request Samples / Quotes / Technical Assistance https://www.linearsystems.com/about-2 Final Thoughts For designers who demand: Low noise High matching precision Low capacitance High input impedance And sonic or measurement transparency The LS844 offers one of the strongest performance combinations in the industry. Whether you are designing a reference-grade audio signal chain  or an ultra-low-current sensor measurement stage , the LS844 provides the clarity, control, and stability  needed for true precision.

In an era dominated by FETs and IC-level integration, it’s easy to forget just how powerful a well-designed bipolar transistor can be. Yet for the analog engineer chasing ultra-low drift, tight matching, and reliable gain stability, bipolar junction transistors (BJTs) remain indispensable. Linear Systems carries forward the legacy of precision bipolar technology with a complete line of monolithic matched dual and single transistors  designed for low noise, high stability, and long-term reliability in demanding analog applications. Why Bipolar Transistors Still Matter Bipolar transistors offer high transconductance, low offset voltage, and predictable linearity —attributes that make them ideal for precision amplifiers, log converters, and differential front ends. While FETs dominate in high-impedance designs, BJTs remain the preferred choice when low noise at higher currents, tight matching, or excellent gain tracking  over temperature are essential. Linear Systems’ monolithic dual transistors combine those advantages with the consistency of devices fabricated on a single die. The Linear Systems Bipolar Lineup Each device family is built on a foundation of precision matching, temperature stability, and proven analog performance. Series Type Configuration Highlights / Applications IT120 / IT124 Series NPN Monolithic Dual Ultra-low drift, ideal for differential input stages LS310 Series NPN Monolithic Dual Tight beta matching for instrumentation and audio circuits LS318 NPN Monolithic Dual Log conformance for log and transimpedance amplifiers LS301 Series NPN Monolithic Dual High-voltage, super-beta design for precision high-voltage amplifiers LS3250 / LS3250S NPN Dual / Single High-speed switching with excellent gain stability LS3550 Series PNP Dual / Single Complementary to LS3250 series for push-pull amplifier design LS350 / IT130 Series PNP Monolithic Dual Tight matching and tracking for low-offset differential stages LS358 PNP Monolithic Dual Log-conformance PNP pair for current-mode and logarithmic circuits Each part is manufactured on Linear Systems’ precision analog processes to ensure gain, offset, and temperature characteristics remain tightly controlled —a vital advantage for applications where unmatched discretes simply can’t deliver. Monolithic Matching for Real-World Precision Unlike discrete matched pairs mounted side-by-side, Linear Systems’ monolithic dual transistors share the same silicon substrate , ensuring both devices track identically over time and temperature. This results in: Exceptional V_BE and beta matching  across the operating range Reduced thermal drift  and offset voltage Improved common-mode rejection  in differential circuits Long-term stability  ideal for metrology, medical, and instrumentation applications Whether you’re designing a precision current mirror, amplifier front end, or logarithmic converter, these transistors ensure your design behaves predictably across environmental extremes. Applications and Design Examples Linear Systems’ bipolar transistors appear anywhere analog accuracy matters: Instrumentation Amplifiers  – Tight beta matching minimizes offset and drift. Audio Circuits  – Complementary NPN/PNP pairs deliver low distortion and consistent tone. Logarithmic and Transimpedance Amplifiers  – LS318 and LS358 provide superior log conformity. High-Speed Switching  – LS3250S single devices handle rapid switching with excellent gain linearity. Precision Current Mirrors  – Matched pairs like the LS310 maintain balance and accuracy even under temperature cycling. For designers upgrading legacy systems or maintaining long-term platforms, Linear Systems’ bipolar families also serve as drop-in replacements  for many classic transistor types from Amelco, National, and Intersil. Designing with Confidence Choosing the right transistor pair often comes down to your application’s operating voltage, gain target, and thermal environment. Linear Systems offers both NPN and PNP duals  with complementary performance, making it straightforward to design push-pull amplifier stages  or balanced sensor inputs . A few design tips: Keep both transistors at the same thermal potential for best tracking. Match emitter resistances in differential applications. For ultra-low drift, pair complementary NPN and PNP devices from the same process family. Review each device’s datasheet for log conformity and beta matching specifications. Legacy of Precision — Built for the Future For over four decades, Linear Systems has specialized in high-performance discrete analog semiconductors —and their bipolar transistor line continues that legacy. As system voltages drop and performance margins tighten, these devices offer the unmatched consistency and analog fidelity  designers still rely on. If your circuit demands accuracy, low drift, and repeatable performance, Linear Systems’ matched bipolar transistors deliver a proven path to precision. Explore the full product line and datasheets: 🔗 linearsystems.com/bipolartransistors Request samples or technical support: 📧 info@linearsystems.com  | Sample Request Form