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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

B1 Buffered Passive Preamp Few names in audio design inspire as much respect as Nelson Pass . For decades, Nelson has pushed the boundaries of amplifier and preamp design with simple, elegant circuits that deliver extraordinary sound quality. His work has shaped the way audiophiles, DIY builders, and even professional engineers think about high-end audio. One of his most enduring contributions is the B1 Buffer Preamp . At first glance, it looks deceptively simple: a unity-gain buffer with just a handful of components. But simplicity is part of the magic. The B1’s performance comes directly from the quality of the devices at its heart — JFETs , chosen for their unmatched noise and linearity characteristics. Why JFETs? JFETs are ideal for front-end and buffer applications because of their: High input impedance  – preventing loading on delicate audio sources. Low output impedance  – ensuring strong, stable drive into power amps. Low noise and excellent linearity  – crucial for preserving the subtle details in music. Nelson Pass has long relied on Linear Systems’ JFETs in this role. In the B1, the complementary pair of N-channel  and P-channel JFETs  provides transparency and neutrality — qualities that have made the circuit famous in the audio DIY community. Linear Systems Inside The classic B1 buffer used the 2SK170 and 2SJ74, but as those parts became scarce, Nelson and the DIY community turned to Linear Systems’ equivalents : LSK170  – N-channel JFET, ultra-low noise, high transconductance, widely used in audio and precision instrumentation. LSJ74  – P-channel complement, designed as a low-noise, high-performance match to the LSK170 . LSK389  – dual, monolithic version of the LSK170 , offering superb device matching and thermal tracking in a single package. By integrating these parts, the B1 achieves a combination of clarity, drive, and quiet backgrounds  that has made it a reference design for both commercial and DIY preamps. Design Philosophy: Simple but Brilliant The B1 isn’t about flashy complexity or an endless parts list. It’s about getting the fundamentals right. Nelson has often said that he prefers simple circuits with the best possible devices , and the B1 reflects that philosophy. With Linear Systems’ JFETs, the B1 offers: Musical transparency  – nothing added, nothing taken away. Reliability and stability  – thanks to tightly controlled device specifications. Enduring accessibility  – DIYers and builders around the world continue to build and enjoy this design. A Partnership Built on Trust Nelson Pass has been a longtime friend of Linear Systems , and his decision to use our JFETs reflects a deep trust in their performance and consistency. From phono stages to amplifiers to buffers like the B1, Linear Systems devices have become a staple in Pass designs. That legacy continues today, as both professional audio engineers and hobbyists choose LSK170 , LSJ74 , and LSK389  as drop-in solutions for their high-end audio projects. Learn More & Build It Yourself The full B1 Buffer schematic and project description are available directly from Nelson Pass at PassDIY – B1 Buffer. Whether you’re an audiophile, a designer, or a curious DIY builder, the B1 is a perfect example of how great devices make great circuits possible . At Linear Systems, we’re proud to see our JFETs featured at the core of such a beloved design. 🔗 View the schematic and project at PassDIY – B1 Buffer .

When designing circuits for test instrumentation , medical electronics , or any system where stable, low current is crucial, the choice of a current-regulating diode (CRD) can make all the difference. Linear Systems’ J500  and SST500  series provide engineers with reliable, tightly specified constant-current performance — even across wide voltage and temperature ranges — while simplifying circuit design. What is a Current Regulating Diode? A current-regulating diode (also called a constant current diode) is a two-terminal device that limits current to a fixed value, regardless of voltage fluctuations within its operating range. Internally, most CRDs use a JFET with the gate tied to the source. Once the device reaches saturation, the current remains steady over a wide voltage swing. This gives designers a simple, compact, and reliable current source  without additional circuitry. Key advantages: Reduced part count compared to op-amp or resistor-based current sources Stable performance across voltage changes Compact and easy to integrate in low-power and battery-driven designs The J500 & SST500 Series at a Glance Feature J500 Series SST500 Series Package TO-92 (through-hole), plus bare die SOT-23 (surface mount), plus bare die Current Range ~0.19 mA to 5.6 mA (nominal) ~0.19 mA to 5.6 mA (nominal) Operating Voltage Up to 50 V Up to 50 V Temperature Range −55 °C to +150 °C −55 °C to +150 °C Forward Capacitance ~2.2 pF (typical) ~1.5 pF (typical) 🔗 J500 Product Page 🔗 SST500 Product Page Why It Matters Tight, predictable performance  — essential for sensitive applications in medical instrumentation and precision test gear. Package flexibility  — TO-92 for prototyping and robust handling, SOT-23 for space-constrained SMT designs. High reliability  — Wide voltage and temperature ratings ensure stable performance even in harsh environments. Simplified design  — Drop-in constant current without biasing networks or active components. Application Examples Driving LEDs or photodiodes with a fixed current, even as supply voltage changes Providing a stable bias for RTDs, thermistors, or strain gauges Current sources in battery-powered medical devices Simplifying constant-current references in test and measurement equipment Choosing Between J500 & SST500 Prototyping / through-hole builds  → J500 (TO-92 package) Compact SMT designs  → SST500 (SOT-23 package, lower parasitics) Custom packaging or tighter screening  → Bare die options available directly from Linear Systems Final Thoughts Linear Systems’ J500 and SST500 current regulating diodes  deliver stable, predictable current regulation in easy-to-use packages. With options ranging from TO-92 to SOT-23 to bare die, and current levels spanning ~0.19 mA to 5.6 mA, these CRDs simplify circuit design while ensuring high performance across demanding applications. 📄 Explore datasheets on our Current Regulating Diodes page ✉️ Contact our applications team at support@linearsystems.com  for design guidance 📦 Request samples to evaluate the J500 and SST500 in your next design Prefer to speak with someone directly? Give us a call at (510) 490-9160 and our team will connect you with the right person.

Detecting the almost undetectable takes extraordinary precision. In fields from seismic monitoring to medical diagnostics, engineers often face a fundamental challenge: the signals they want to measure are buried in noise. A few picoamps of current or microvolts of voltage can hold crucial information — but only if your circuit can hear it. That’s where Linear Systems’ ultra-low noise JFETs  come in. Why JFETs Excel at Quiet Signal Detection JFETs are inherently low-noise devices, and Linear Systems’ precision-matched small-signal JFETs take that advantage even further. Parts like the LSK170  and LSK389  are designed to deliver exceptionally low gate current and noise density , making them ideal for high-impedance sensors such as: Geophones and seismometers Photodiodes and avalanche photodiodes (APDs) Ionization chambers and radiation detectors Precision strain gauges and MEMS sensors With input noise voltages measured in nanovolts per √Hz, these devices help engineers extract meaningful data where other devices see only static. Real-World Impact When paired with precision resistors and low-leakage capacitors, Linear Systems’ JFETs form the heart of front-end amplifier stages that must preserve signal integrity from the very first electron. They enable: Higher sensitivity  — Detect smaller signals without sacrificing SNR Wider dynamic range  — Maintain linearity from picoamps to milliamps Temperature stability  — Maintain accuracy in harsh or cryogenic environments Engineers worldwide rely on these JFETs to design instrumentation that can measure the imperceptible — from tracking tectonic drift to detecting a single photon. Bringing It All Together Ultra-low noise front ends start with the right transistor. Explore Linear Systems’ JFET portfolio to see how you can push your design’s sensitivity limits: 🔗 View our JFET product family 🔗 Request free engineering samples 📞 Call us at (510) 490-9160 or   📧 Email support@linearsystems.com

Precision Protection for Precision Circuits In modern high-impedance analog systems, every picoamp counts . When your front end is measuring nanoamps—or even picoamps— microamp-level diode leakage can swamp the signal , distort measurements, and silently undermine performance. That’s why designers turn to Linear Systems’ PAD and DPAD Series Low Leakage Diodes —purpose-built to deliver ultra-low reverse leakage , low junction capacitance , and exceptional thermal stability . Why Low Leakage Matters Standard silicon diodes can leak nanoamps to microamps , which becomes significant in sensor and measurement circuits. Linear Systems’ PAD and DPAD Series diodes achieve reverse leakage in the picoamp range , even across temperature extremes, helping engineers maintain accuracy and repeatability. Key benefits: ⚡ Ultra-low reverse leakage  → preserves accuracy in high-impedance circuits 📉 Low junction capacitance  → maintains bandwidth and reduces distortion ♨️ Thermally stable  → consistent performance over temperature 🛡️ Fast recovery  → protects sensitive nodes without adding error The Product Families PAD Series – Single Low Leakage Diodes Industry-leading reverse leakage in the picoamp range Ideal for guarding, clamping, or protecting single high-impedance nodes Common part numbers: PAD1, PAD2, PAD5 DPAD Series – Dual Matched Low Leakage Diodes Two matched low-leakage diodes on the same die Excellent thermal tracking and symmetry Ideal for differential sensor front ends, precision measurement bridges, and long-term stability Common part numbers: DPAD1, DPAD2, DPAD5 Where They’re Used Today Precision Measurement & Test Equipment Guard diodes and clamps in electrometers, picoammeters, and high-impedance voltage dividers Leakage-sensitive front ends in source-measure units (SMUs) and photodiode amplifiers Sensor Interfaces Protecting ADC and amplifier inputs in spectroscopy, photometry, and bio-sensing systems Limiting charge injection in capacitive or charge-redistribution sensors Low-Noise Analog & RF Systems Bias stabilization and protection in ultra-low-noise audio preamps, RF front ends, and oscillators Diode clamps in high-impedance nodes to prevent overvoltage without adding leakage Industrial & Aerospace Systems Monitoring high-resistance networks (e.g., insulation monitors) where leakage corrupts readings Long-duration missions where diode stability over decades is crucial Summary Leakage currents that were once negligible are now design-limiters. Linear Systems’ PAD and DPAD Series Low Leakage Diodes  give engineers the picoamp-level assurance  they need to build stable, accurate analog systems in today’s high-impedance designs. If your front end needs to stay quiet and accurate— start by eliminating the leakage. 👉 Request Samples Here Have technical questions, need a quote, or looking for more information? Our engineers are here to help: 📞 Call us at (510) 490-9160 or   📧 Email support@linearsystems.com

When it comes to photodiode front ends, noise and stability  are the real challenges. Photodiode capacitance can destabilize feedback loops, while input bias current and 1/f noise often dominate performance at low signal levels. Designing a transimpedance amplifier (TIA) that maintains accuracy across temperature and frequency isn’t trivial. That’s where Linear Systems’ single JFETs —the LSK170 and upcoming BF862 replacement —shine. Both provide ultra-low leakage, low noise, and high input impedance, making them ideal for photodiode buffering in precision TIAs. Why Use a JFET Front End? Many TIAs rely solely on op-amps. But at high feedback resistances— 1 MΩ and above —input bias current quickly turns into millivolts of error. A JFET buffer solves this by isolating the op-amp from the photodiode capacitance and keeping gate currents in the picoampere range . Key benefits of using LSK170 or BF862 replacement in photodiode TIAs: Ultra-low gate leakage  → minimizes dark current and DC errors. Low 1/f noise  → critical for low-frequency sensor and instrumentation applications. High input impedance  → supports large-value feedback resistors without loading effects. Bootstrapping effect  → reduces effective photodiode capacitance, improving stability and bandwidth. Example Design – Single JFET-Buffered TIA A widely used approach is to buffer the photodiode with a single JFET ( LSK170 or BF862 replacement)  before the op-amp’s inverting input. RF = 1 MΩ CF = 0.5–2 pF  (for stability compensation) Photodiode capacitance:  2–10 pF Supply: ±12 V to ±15 V This configuration provides: Gain: ~1 V/µA (1 µA photocurrent → 1 V output) Bandwidth: >100 kHz (depending on photodiode capacitance and compensation) Noise: dominated by RF’s Johnson noise, with minimal added contribution from the JFET. Bench Results In lab tests with an ~8 pF silicon photodiode and modulated LED source: Step response:  clean at 100 kHz with <10% peaking. Noise: only a few µVrms (20 Hz–100 kHz). Offset drift:  stable within millivolts from 25 °C to 60 °C. These results confirm that using a single JFET like the LSK170 or BF862 replacement  yields quiet, stable TIAs without added complexity. Applications Optical sensors  – spectrometers, fluorescence detectors, LiDAR receivers Scientific instrumentation  – low-light measurement, precision photometry Industrial monitoring  – process control, position sensing, safety systems Audio front ends  – ultra-low-noise preamps for microphones and pickups Advanced Option – Using the LSK389 Dual For most single-ended photodiode TIAs, the LSK170 or BF862 replacement  is the best choice. However, engineers needing even lower noise or matched pairs  can consider the LSK389 dual JFET : Use one half  as a drop-in replacement for a single JFET. Parallel both halves  for ~3 dB lower voltage noise (at the cost of ~2× leakage). Matched dual geometry  ensures excellent thermal tracking, ideal for differential photodiodes or ultra-stable instrumentation. Summary Photodiode TIAs demand a careful balance of speed, noise, and stability . By combining a low-noise op-amp with a Linear Systems JFET buffer , designers can achieve: Picoamp-level input bias currents Low 1/f noise Stable operation with high feedback resistors Choose your device: LSK170 / BF862 replacement  → best for single-ended TIAs, cost-sensitive designs, and wide adoption. LSK389 dual  → premium option for ultra-low drift, differential front ends, or noise-critical systems. 👉  Explore Linear Systems’ LSK170 , BF862 replacement, and LSK389 JFETs  for your next optical front-end design.