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In March 2021, NASA published a pivotal report— NASA/TM‑20210009960 —evaluating Linear Systems’ dual N-channel Junction Field-Effect Transistors, the LSK389 and LSK489 , under conditions that mimic the harsh radiation environment of space. The study assessed both Total Ionizing Dose (TID)  effects at cryogenic temperature (−65 °C) and Single-Event Latchup (SEL) vulnerability under heavy ion exposure. With their application in sensitive space missions like the Ocean Color Instrument (OCI) on the PACE spacecraft, confirming these JFETs’ resilience is critical. Test Objectives & Rationale The tests aimed to: Determine if high-energy heavy ions could induce “latchup”—a destructive form of failure—despite the shared substrate between the JFET pairs, which could behave like a parasitic p–n–p–n structure. Evaluate long-term exposure to gamma radiation (TID), up to tens of krad(Si), with the transistors operated at −65 °C to simulate real-world space thermal conditions. Experimental Setup SEL Testing : Conducted at Lawrence Berkeley National Lab’s 88-inch cyclotron using intense 1,039 MeV silver ions (LET 48.15 MeV·cm²/mg). Both “substrate bonded to drain” and “floating substrate” configurations were tested at room temperature—conservatively more challenging than the target −65 °C. TID Exposure : Performed at NASA Goddard’s Radiation Effects Facility. Each JFET variant was irradiated in steps (1, 3, 6, 12, 25 krad(Si)), with devices kept biased and cold. Parametric measurements (drain current IDS, gate leakage IGS) were taken before and after each dose. Key Findings SEL Immunity : No high-current latchup occurred during aggressive heavy-ion testing—even with floating substrates and at room temperature. Given the harsher testing conditions, the parts are effectively SEL-immune at actual mission temperatures. TID Performance : Up to 25 krad(Si), both JFETs maintained electrical performance within specifications. Minor parameter shifts were attributed to measurement noise rather than degradation. Detailed Results The report includes extensive parametric tracking—IDS and IGS over key voltage operating points across each dose step. It notes that variations observed after ~6 krad(Si), which is the qualification dose for OCI, fell within expected noise bounds, with averages used to present robust results. Conductively and non-conductively bonded samples performed statistically the same. Implications for Space Applications SEL Immunity : The absence of latchup in even the most vulnerable substrate configuration under heavy-ion bombardment is compelling evidence of the JFETs’ safety for space missions. TID Durability : Stable performance through relevant radiation doses confirms their suitability for long-duration scientific instruments and deep-space missions. Design Confidence : Engineers can rely on these JFETs for precision front-end amplification in high-reliability systems, knowing radiation-induced failures are highly unlikely. Conclusion NASA’s exhaustive testing of the LSK389 and LSK489 demonstrates that both JFETs are well-suited for demanding space environments. Their combined resilience to SEL and TID effects positions them as strong candidates for use in sensitive instrumentation, such as low-noise photodiode readouts and scientific payloads aboard satellites. For a deeper dive into the data or experimental methodologies, the full technical memorandum (NASA/TM‑20210009960) is publicly available via the NASA Technical Reports Server ( ntrs.nasa.gov ).

At Linear Integrated Systems, we love shining a spotlight on JFET technology and the classic analog circuits that showcase its unique advantages. This week for #FETFriday, we're highlighting one of the most fundamental JFET configurations: the Common-Source Amplifier . What is a Common-Source JFET Amplifier? The common-source amplifier is a go-to building block in analog design. Much like the common-emitter stage in a BJT amplifier, this configuration offers voltage gain  and is known for its high input impedance , low noise characteristics , and simplicity . It uses an N-channel JFET with the source terminal grounded (hence "common source") and the signal applied to the gate. A load resistor is placed at the drain, and biasing resistors ensure the transistor operates in its active region. Here’s a simplified schematic from Electronics-Tutorials.ws : Key Components: N-Channel JFET  (such as the LSK170 or LSK389 for low-noise applications) Bias resistors  to set gate voltage Source resistor  for stability (can be bypassed with a capacitor for increased gain) Drain resistor  as the load Why Use a JFET in This Configuration? JFETs offer an exceptionally high input impedance—ideal for buffering sensitive analog signals. When configured as a common-source amplifier, the JFET’s low gate leakage and voltage-controlled nature allow for clean signal amplification with minimal distortion. At Linear Systems, our parts like the LSK389 , LSK170 , and LSJ74  are optimized for low-noise and precision audio or instrumentation designs—making them excellent choices for this topology. Applications You’ll find this configuration in: Audio preamplifiers Sensor front ends High-impedance measurement circuits Low-noise RF circuits Learn More To dive deeper into the operation and theory behind the Common-Source JFET Amplifier, check out the full article:👉 Common-Source JFET Amplifier – Electronics-Tutorials.ws Got a favorite JFET design or a question about our parts? Drop a comment or connect with us!Stay tuned for more analog fun next #FETFriday!

In the world of electronics, precision and reliability are key. One of the unsung heroes that helps ensure smooth, distortion-free operation is the bipolar transistor. These small yet mighty devices play a pivotal role in amplifying or switching electrical signals across a variety of applications, from audio systems to power electronics. At Linear Systems, we have been pushing the boundaries of innovation in transistor technology since 1984, providing engineers with high-quality solutions for their most demanding designs. In this blog post, we’ll dive into the features, benefits, and diverse applications of our bipolar transistors, exploring how they are used in everything from cutting-edge audio systems to advanced communication devices. What Makes Linear Systems' Bipolar Transistors Stand Out? Low Noise and High Gain When it comes to precision electronics, few things matter more than noise and gain. Linear Systems’ bipolar transistors are engineered with both low noise and high gain, which makes them ideal for applications where signal clarity is critical, such as audio amplifiers. Whether you’re designing a high-fidelity audio system or a sensitive sensor, these transistors ensure that even the faintest signals are amplified with minimal distortion. High Current Handling Another standout feature is their ability to handle high currents. This capability is particularly beneficial in power electronics, where maintaining efficiency and thermal management is crucial. By handling large currents with ease, our bipolar transistors provide the stable performance needed for power supplies, motor control circuits, and more. The Real-World Benefits of Linear Systems’ Bipolar Transistors Enhanced Signal Quality and Better Performance Thanks to their low noise and high gain properties, our bipolar transistors significantly improve signal quality, which is crucial in communication systems. In the world of modern electronics, even the smallest distortion can lead to significant issues. Our transistors help eliminate that problem, ensuring that your circuits perform at their best, every time. Power Efficiency and Longevity In today’s energy-conscious world, efficient power management is more important than ever. Our bipolar transistors not only manage power effectively but also help reduce overall power consumption. This results in longer battery life for portable devices and a more sustainable use of energy in larger systems. It's the perfect balance of power and performance. Versatile Applications Across Industries Our bipolar transistors are trusted in a variety of applications, providing engineers with the flexibility and reliability they need to tackle a wide range of challenges. Some of the key areas they excel in include: Audio Amplifiers and Preamplifiers : For pristine sound quality and low distortion. Power Supplies : Ensuring stable voltage and current for sensitive electronics. Switching Circuits : Reliable and fast switching for efficient circuit control. Motor Control Circuits : Perfect for precise motor speed and direction control. LED Drivers : Ensuring the efficient operation of LED-based systems. Moreover, these transistors are a staple in communication systems, from radios to cell phones, ensuring that your devices operate smoothly with optimal signal clarity. Conclusion: Trust Linear Systems for Superior Performance When you choose Linear Systems’ bipolar transistors, you're opting for unmatched quality, reliability, and performance. From their low noise and high gain characteristics to their ability to handle high currents, our transistors are built to deliver the best in every application. Whether you’re designing a sophisticated audio system or a cutting-edge communication device, you can rely on our bipolar transistors to meet your needs and exceed your expectations. Ready to take your design to the next level? Explore our Bipolar Transistors  and discover how they can optimize the performance of your next electronic project. Explore Our Bipolar Transistors: Click here to view our full range of bipolar transistors and see how they can enhance your designs.

In July 2002, Tape Op featured Scott Hampton’s ultra-simple, ultra-musical DIY JFET Mic Preamp , a solid-state marvel emulating tube-like warmth without the hassles of high-voltage supplies. Hampton called it a "solid‑state tube"—a nod to how closely a JFET can mimic the behavior and sonic character of a triode. ( Tape Op ) Figure 1 – The “Solid‑State Tube” Figure 1 juxtaposes a classic N-channel JFET class-A stage with a triode tube amplifier. They’re functionally identical: both offer high input impedance, soft saturation, and effortless gain. In Blind A/B comparisons, many listeners preferred the JFET version, praising its clean highs and tight bass—even alongside the tube circuit. ( Tape Op ) Why it matters:  It visually demonstrates why we love using JFETs like LSK189/389  in audio—organic response without the complexity of tube gear. Figure 2 – The Build‑Ready JFET Module Figure 2 transitions from theory to application. It’s the complete circuit: JFET (e.g. 2N5457, or better—LSK189/LSK389) 15 kΩ drain resistor to 9–24 V supply 50 Ω unbypassed source resistor + 470 µF bypass —cuts 3rd harmonic by ~20 dB NPN Darlington buffer (MPSA14 / ZTX653)  for low-impedance output Coupling capacitor  on output to block DC offset Approximately +26 dB gain , with high input impedance (~1 MΩ) ( diyAudio , Tape Op ) This design gives a clean gain stage with a mild but useful amount of JFET-driven harmonic coloration. The voltage-follower stage ensures you can drive downstream gear with confidence. Applications & Advantages 1. Microphone Preamp Stack two of these modules, add a mic transformer and gain pot—voilà, a rich, transformer-balanced mic preamp. The high input impedance works wonders with ribbon, electret, and piezo mics. 2. Guitar/Instrument Preamp Just one stage with output pot transforms a guitar pickup into an amp-ready signal—class-A mojo in pedal-friendly format. 3. Sonic Character & Distortion Control Staging multiple modules or subtly increasing gain introduces pleasing saturation. The 50 Ω unbypassed Rs tempers highs, taming harsh harmonics while retaining clarity. Many DIYers build dual-stage versions with level controls on each for saturation orchestration. ( Tape Op , GroupDIY Audio Forum ) Supercharge With Linear Systems JFETs Replace  generic FETs with LSK189  (single) or LSK389  (matched dual) for exceptional performance: low noise (~0.9 nV/√Hz), low leakage, and superb frequency response. Why switch?  The stock 2N5457 offers a great starting point, but LSK-series JFETs bring studio-grade sound, especially beneficial for ribbon mics and piezo pickups. 💡 Learn More & Resources Original Tape Op 2002 Article  detailing Figures 1 & 2 and timestamped examples: “DIY JFET Mic Pre: Build Your Own Studio Preamp”  by Scott Hampton. ( Gearspace , Tape Op ) Hamptone kits (HJFP1/HJFP2)  – built around this JFET module: learn via Ralf Kleemann’s build log. ( kleeworld.de ) Reviews  – from gearspaces like Gearspace/GroupDIY: users praise its mojo and clean-to-gritty transition. ( Gearspace ) Linear Systems JFET catalog  – explore datasheets for LSK189 and LSK389 at linearsystems.com

Designing ultra-low-noise circuits often means balancing trade-offs between gain, distortion, and complexity. One proven technique for minimizing noise in differential amplifier stages is the use of cascode structures. Below, we explore three cascode variations and how each impacts noise performance and distortion. (a) Bipolar Cascode – Highest Noise In this configuration, a bipolar transistor is used in the cascode stage. While effective in many designs, the high base current of bipolar devices introduces significant noise. This makes it the noisiest of the three structures. (b) JFET Cascode – Lower Noise Replacing the bipolar transistor with a JFET greatly reduces input current, thanks to the JFET's extremely low gate current. The result? Lower overall noise compared to the bipolar version. This structure is ideal for applications requiring improved signal integrity. (c) Driven Cascode – Lowest Distortion The final circuit goes a step further. Known as a driven cascode , this configuration virtually eliminates input capacitance through a bootstrapping effect created by the JFETs. Not only does this help reduce noise, but it also dramatically lowers intermodulation distortion—making it the cleanest option for precision analog designs. Whether you're working on sensitive instrumentation, high-end audio, or RF front ends, these cascode techniques can help you achieve cleaner signals and higher performance. 🔗Want to dive deeper? Check out our full LSK489 Application Note here: https://www.linearsystems.com/applicationnotes/lsk489-app-note

For our FET Friday post we are revisiting the timeless Op‑Amp Cookbook, Part 1  by Ray Marston, which reminds us how fundamental op‑amp principles remain the bedrock of analog design, even in today’s high-performance landscape. If you're up for a refresher, check it out here: Op‑Amp Cookbook — Part 1 . At Linear Systems, we believe in building on those fundamentals—using precision components like the LSK389 —to bring classic designs into the modern era. Insights from Part 1 of the Op-Amp Cookbook Marston lays the groundwork with clear block diagrams and practical circuit examples. He describes the op‑amp as a high‑gain, direct‑coupled amplifier  featuring inverting and non‑inverting inputs with offset‑compensation and output stages powered by both ± and common rails. He then walks through fundamental topologies: Inverting Amplifier : Offers predictable gain via resistor ratio; bandwidth shrinks as gain increases. AC‑Coupled Inverting Amplifier : Introduces coupling caps for DC rejection, removing the need for offset nulling. Non‑Inverting Amplifier / Voltage Follower : Provides high input impedance and unity gain buffering. Bootstrapping & High‑Impedance Techniques : Expands input impedance into megaohm ranges using feedback or guard rings. These circuits highlight essential truths—bandwidth constraints (via gain-bandwidth product), offset considerations, and impedance management—that remain relevant in high-precision design. Elevating Classic Circuits with the LSK389 Our LSK389 ultra‑low‑noise monolithic dual JFET  dramatically improves performance when integrated into these classic op‑amp stages: The LSK389  is renowned as perhaps the lowest-noise dual JFET in its class— rated at ~1.9 nV/√Hz  at 1 kHz, with 100% noise testing  to eliminate burst/popcorn noise. ( Linear Systems ) It features tight matching , excellent thermal tracking , low capacitance (~25 pF) , and high breakdown voltage , making it ideal for sensitive front-end designs. ( Linear Systems ) How It Enhances Key Configurations: Original Circuit Typical Challenge How LSK389 Helps Inverting / Non‑Inverting Input noise, bias instability Ultra‑low noise, low bias current, high input impedance Differential / Instrumentation Matching and drift Monolithic, tightly matched pair ensures low offset and drift Bootstrapped / High‑Z Leakage and loading Low capacitance preserves high impedance integrity Sensor / Audio Preamps Weak signal fidelity Lowers noise floor dramatically for sensitive analog paths Cascode / Bias Circuits Stability and drift Matches and thermally tracks for stable, precise biasing The integrated dual JFET structure means excellent matching for differential and instrumentation stages. Its low input capacitance supports high-speed operation without undue loading. Real-World Application: Discrete JFET Front-End Consider placing an LSK389 input stage before a standard op-amp: You get ultra-low-noise buffering using the LSK389, followed by the op-amp’s gain stage. The result? A cleaner, quieter overall signal chain, ideal for audio, instrumentation, or sensor systems where signal fidelity matters. By pairing Marston’s Op-Amp Cookbook, Part 1  foundational designs with the precision capabilities of the LSK389 , you get the best of both worlds: classic analog theory operationalized through high-performance hardware. So… what do you think? Old news, or still deeply relevant? For samples of the LSK389, or any Linear Systems parts, complete our request form , or email support@linearsystems.com .

In our last blog, we revisited Ray Marston’s classic Op-Amp Cookbook – Part 1  and explored how its timeless design principles continue to resonate with today’s engineers. Now, we’re diving into Part 2 of the series , originally published in Nuts & Volts Magazine  (August 2001). This installment moves from basic op-amp operation into practical design territory—linear amplifiers and active filters. Although the circuits featured in the article are designed around the classic 741 op-amp, the principles remain directly relevant to modern designs, especially when paired with the low-noise, high-performance devices available today. Key Takeaways from Part 2 1. Inverting and Non-Inverting Amplifiers Marston details classic configurations for both DC and AC amplification. Input/output impedance control and offset nulling are emphasized for achieving stability and precision. These remain foundational building blocks for analog designers. 2. Voltage Followers The voltage follower (unity-gain buffer) provides high input impedance and low output impedance—crucial in isolating circuit stages. While the 741 was the reference device in the article, today’s applications demand lower noise, higher bandwidth, and stability at unity gain. 3. Adders and Subtractors Summing amplifiers and differential subtractors are shown as tools for audio mixing, precision measurement, and signal conditioning. These circuits illustrate how op-amps bring flexibility to multi-input and comparison-based designs. 4. Active Filters Marston demonstrates how op-amps can be used to implement Butterworth low-pass, high-pass, and band-pass filters. These “active filters” reject unwanted frequencies without bulky inductors, paving the way for compact analog solutions that are still widely applied. Where Linear Systems Fits In At Linear Integrated Systems, we design low-noise, high-precision discrete semiconductors  that give these foundational circuits new life in demanding modern applications. For example: Our LSK389 dual JFET  can be paired with op-amp filter stages to achieve ultra-low-noise performance in audio and instrumentation. The LSK170/LSJ74  devices provide excellent input stage options for non-inverting high-impedance amplifiers. Precision current sources like the J202 and J113 families  complement voltage follower and filter designs that require tight current control. By substituting these devices into Marston’s foundational topologies, designers can push performance beyond the limitations of legacy 741 op-amps—achieving lower distortion, wider bandwidth, and quieter operation. Why It Still Matters Analog isn’t going away—it’s evolving. These foundational op-amp circuits continue to form the backbone of countless modern designs, from audio preamps to sensor front-ends and precision measurement equipment. Pairing the timeless principles from Op-Amp Cookbook Part 2  with the performance of Linear Systems devices helps bridge the gap between theory and modern application. So what do you think— is this “old news,” or is it still the analog engineer’s playbook? 👉 Explore our product portfolio at www.linearsystems.com  and see how our devices can bring new precision to proven circuit concepts.

Analog Performance Without Compromise In today’s world of high-resolution audio, sensitive instrumentation, and precision sensing, one component can make all the difference between a good design and a great one. The LSK170 Series  from Linear Systems delivers ultra-low noise performance , exceptional linearity, and the flexibility engineers need to push their designs further. Why Engineers Choose LSK170 Ultra-Low Noise Floor  – Just 1 nV/√Hz at 1 kHz ensures pristine signal fidelity. Wide IDSS Selection  – Multiple bins for easier circuit biasing and consistent results. High Input Impedance & Low Capacitance  – Perfect for high-impedance sources and sensitive measurement systems. Pin-for-Pin Compatibility  – Direct replacement for Toshiba 2SK170, with enhanced performance. Flexible Packaging  – Available in TO-92, SOT-23, SOT-89, and bare die (die form)  for maximum design versatility. Built for the Most Demanding Applications Whether it’s audio preamps, hydrophones, CT scanners, vibration sensors, or electrometers , the LSK170 thrives in environments where every nanovolt matters. Its proven reliability, U.S. manufacturing, and virtually zero popcorn noise make it the choice of professionals and DIY enthusiasts alike. Why LSK170 Matters Today Classic JFET performance meets modern manufacturing. By combining high transconductance, robust breakdown voltage, and industry-leading noise performance , the LSK170 keeps analog design relevant—and powerful—in today’s high-tech world. Want to See the LSK170 in Action? We’re offering free samples  to qualified engineers who want to evaluate the LSK170—or other Linear Systems parts—in their own designs. 👉 Request Your Sample 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

Looking for a smart way to keep your signal levels steady in radar or drone systems? This clever AGC (Automatic Gain Control) design uses a JFET as a voltage-controlled resistor to dynamically manage amplifier gain. At the heart of the circuit is a non-inverting op-amp whose gain is controlled by the resistance between the JFET's drain and source. The op-amp output feeds a full-wave rectifier, which then drives an integrator. Acting as a low-pass filter, the integrator smooths out ripple for lower distortion and more consistent performance. The op-amp + diode configuration delivers a rectified DC voltage proportional to the input signal. This voltage adjusts the JFET’s resistance, which in turn fine-tunes the amplifier’s gain to maintain a steady 0.2V peak-to-peak output—ideal for close-range detection. Originally designed for radar-seeking systems, this robust AGC circuit is just as relevant today in autonomous vehicles and drones, where real-time responsiveness and stability are key. 📚 Source: C. Marco, “Automatic Gain Control Operates Over Two Decades,”   Electronics , Aug. 16, 1973; reprinted in Circuits for Electronics Engineers , 1977.

When you're measuring the faintest electrical signals produced by the brain and heart, any noise, leakage, or delay can corrupt the diagnostic data. That’s why precision diagnostics demand clean analog switching , with speed and signal integrity that traditional switches simply can’t deliver. ⚡ Why Speed and Leakage Matter in EEG/EKG Design High-Speed Matters : With switching speeds under 1 ns, you avoid temporal distortion. Fast switching means less glitching when you're sampling at high rates—critical for capturing accurate waveforms for both EEG (0.5–100 Hz) and EKG (up to 150 Hz) signals. Ultra-Low Leakage (Nanoamps) : In high-impedance front-ends, leakage currents—even just a few nanoamps—can introduce bias errors or drift, compromising measurement precision. Low leakage ensures your signal chain remains true to the physiology. ( analog.com ) Minimal Capacitance & Charge Injection : Low capacitance reduces filtering effects at high frequencies, while low charge injection prevents voltage spikes during switching, keeping analog fidelity intact. ( analog.com ) 🔍 Introducing the SST210: Built for Precision Our SST210  analog switch hits all the marks: Feature Spec Why It Matters Switch-on time < 1 ns Preserves waveform fidelity Reverse capacitance ~0.2 pF Minimizes signal distortion ( mouser.com , electronicspecifier.com ) Leakage current Nanoamp-level Avoids bias and drift in high-impedance EEG/EKG inputs Low ON-resistance Guaranteed Maintains consistent gain and low signal loss Single-supply operation Simple + drive requirements Keeps your front-end compact and reliable This makes the SST210 ideal for sensitive front-end paths like sample-and-hold circuits, measurement multiplexers, deglitch circuits in DACs, and EEG/EKG monitoring front-ends. 🧠 The Role of Clean Switching in EEG/EKG Accurate Amplification: EEG and EKG signals typically sit in the microvolt to millivolt range. Any offset current—especially in the nanoamp range—can shift baselines or distort peaks, skewing diagnostic readings. High-Resolution Sampling: Bio-signal pipelines use anti-aliasing filters tuned just above signal bandwidth. Fast, glitch-free switching ensures these filters work as intended, without introducing jitter or settling delay ( mouser.com ). Reliable Multiplexing: Systems often share ADCs across multiple channels. Clean switching is essential when sampling multiple leads/channels tightly—for instance, when recording dozens of EEG electrodes or precordial EKG leads. 🛠️ How to Integrate the SST210 Front-End Placement : Use the SST210 directly before the input buffer/amplifier. Its low leakage protects against bias creep. Drive Supply : A single 5 V rail is all that’s needed—no complex gate drivers required. Mounting : The SOT‑143 package is compact and easy to route on high-density PCB layouts. Testing Protocols : Evaluate the switch in your actual signal chain with known microvolt-level inputs to measure added noise, offset, and settling behavior. 🎁 Try It for Yourself We’re offering free SST210 samples to qualified engineers  so you can test its performance in your EEG/EKG designs without cost or risk. 👉Complete our samples request form:  https://www.linearsystems.com/about-2 Don’t settle for analog switching that compromises your diagnostic signal. Let the SST210 give your biomedical systems the signal clarity they deserve— down to the nanoamp . Precision diagnostics start with precision switching. Claim your free sample and elevate your design today!

There are three types of amplifiers that are most often used in the design of sensor signal chains. Two of the more popular include the transresistance (transimpedance) amplifier and the charge amplifier. Additionally, there is the voltage amplifier which is often used with sensors that incorporate their own JFET. The transimpedance amplifier is used to convert a current to a voltage. Specifically, its gain can be specified in volts/A. A charge amplifier on the other hand is used to convert a charge to a voltage. A charge amplifier invariable uses a feedback capacitor to configure the amplifier as an integrator. The integrator effectively produces an output voltage that is proportional to the time rate of change of charge.   Transimpedance amplifiers, for the most part, are used in light or electromagnetic based sensor applications. Specifically, the current from a photodiode or a photodetector (induced from the light that strikes it) is converted to a voltage. On the other hand, charge amplifiers, are most often used with piezoelectric based sensors such as piezoelectric bases accelerometers, shock sensors, pressure sensors and hydrophones. However, it is still not uncommon to see piezoelectric sensors used with standard common source amplifiers. Photodiodes are also used with charge amplifiers. Often the selection of the amplifier is based on the characteristics of the sensor or detector used and the performance requirements of the system. Manufacturers will often integrate JFETs into their detectors or sensors to simplify the amplifier interface process. However, for high end performance applications, sophisticated JFET based preamps will be used to supplement the on-board JFET or the sensor will be purchased without the JFET. TRANSIMPEDANCE AMPLIFIER SENSOR APPLICATIONS   The transimpedance amplifier is most often used in photodiode (photodetector) applications often used in a photo optical system. They are used across the electromagnetic frequency spectrum to determine the electromagnetic or light intensity that strikes a surface of the photodetector. This includes light in the gamma ray, X-ray, ultraviolet, visible light, near infrared, mid infrared and far infrared ranges.   The most simplistic topology of the transimpedance amplifier is shown in Figure 1. A current source provides the current that flows through the feedback resistor of the op-amp. This results in an output voltage that is directly proportional to the input current. The feedback resistor determines the transimpedance or transresistance gain, V/I.   A more real-life circuit is shown in Figure 2. It contains a feedback capacitor to prevent oscillations that are a result of parasitic capacitances. The feedback capacitor will affect the AC voltage gain and the stability of the circuit. Oscillations must be designed out.   Explore more about these fascinating concepts and discover industry-leading FETs at Linear Systems: www.linearsystems.com . Stay tuned for our insightful FET Friday posts by following us on LinkedIn !

At Linear Integrated Systems, we know that performance, reliability, and precision are non-negotiable when it comes to analog front-end design. That’s why we developed the LSK389 , a monolithic dual JFET that offers best-in-class low noise, tight gain matching, and outstanding thermal stability. What Makes the LSK389 Unique? The LSK389 is built on a single piece of silicon , giving it superior symmetry and performance consistency over temperature. This eliminates the mismatch and drift often seen with discrete JFET pairs, making it a go-to solution in audio, medical, instrumentation, and defense applications . Key Performance Advantages: Ultra-Low Noise : Ideal for low-level signal amplification in sensitive analog circuits. Precision Matching : Designed for applications requiring tight differential performance. Thermal Stability : Minimal drift ensures long-term reliability across wide temperature ranges. Whether you're working on high-end audio preamps, precision medical instrumentation, or low-drift sensor interfaces , the LSK389 offers the performance edge you need. Want to See the LSK389 in Action? We're offering free samples  to qualified engineers who want to evaluate the LSK389 in their designs. 👉 Request Your Sample Here About Linear Integrated Systems With over 35 years of semiconductor innovation, Linear Systems designs and manufactures high-performance discrete components with a focus on JFETs, bipolar transistors, DMOS switches, and more. Learn more at www.linearsystems.com .