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RF Engineers know that temperature effects matter in RF measurement. This constant temperature substitution design tackles that challenge in a clever way using pico-amp diodes.   JFET Design Spotlight - A Radio Frequency RMS Metering Circuit   “When Linear Technology introduced the LT1088 RMS converter, it was packaged in a complicated iso-thermal DIP package to allow the published RMS measuring circuit application some working room. The problem with that application was temperature increasing with measured power allowing only limited precision and repeatability over environmental temperature fluctuations. However, by using the additional concentric 250Ω resistors, another control option was obviously available creating possible constant temperature operation regardless of input power measured. Here, the 250Ω resistors raise the Die temperature to about 40°-60°C where any additional thermal influence of incoming RF can be substitute balanced by complimentary reduction of the 250Ω power input. Common mode voltage of the LT1088 D1&D4 diodes sets the temperature and differentially balances out the input RF at 50Ω  with a DC equivalent power at 50Ω. The Voltage across D1&D4 are therefore constant for the input measurement range of 80mW. I talked Jim Williams out of some plastic packaged LT1088’s to prove that the expense of isothermal packaging was unnecessary. Accuracy improved over 10-fold from the original application circuit. As is the case for many of these instrument circuits, Clamp and level fixing diodes used with FET input Op-Amps by habit use pico-amp diodes like the LIS PAD-1‘s. By the way, Dual PAD pico-amp diodes have a little known feature of exhibiting significantly less nodal leakage than the Datasheet illustrates when used in symmetrical clamp bias function as shown in the earlier published 10Kv amplifier protection. These on DIE diode pairs function similarly to the gate bias cancellation of dual pico-amp JFET’s illustrated in the Accelerometer circuit presented earlier. Close proximity allows uniform doping distribution and nearly perfect matching for Dual PAD diode parts so symmetric bias currents balance to near nothing. For me, it’s a time-tested habit.” Kirkwood Rough   Why this matters:   Improved measurement accuracy through thermal stability Symmetrical diode behavior enables ultra-low leakage performance A great example of where Linear Systems PAD pico-amp diodes shine   Looking for ultra-low leakage diode solutions for your next design? Our PAD series offers exceptional matching and performance for precision analog and RF applications.   Have you used pico-amp diodes in similar circuits or solved temperature stability challenges in a different way? Share your experience in the comments.   Learn more and request samples in the comments.   #AnalogDesign #RFEngineering #JFET #ElectronicsDesign #LowNoise #Semiconductors #LinearSystems

Every engineer has faced it at some point: a critical component in your design is suddenly obsolete, unavailable, or impossible to source reliably. And unlike digital systems, analog designs don’t always give you the luxury of a quick swap. So what do you do when a key part disappears? Why Obsolescence Hits Analog Designs Harder In digital design, you can often work around a part change with firmware or minor adjustments. In analog circuits, even small parameter differences can create real problems. Things like noise performance, matching, leakage current, and biasing behavior are tightly tied to how the circuit performs. A “close enough” replacement can easily lead to increased noise, drift in operating points, degraded signal integrity, or even a full redesign. What Engineers Are Running Into Right Now From conversations with engineers and customers, a few patterns come up consistently. Legacy parts are disappearing, especially widely used JFETs and small-signal devices. Supply is often unpredictable, with long lead times or inconsistent availability. Secondary markets introduce risk, including counterfeit or non-conforming parts. And in many cases, redesign simply isn’t practical, especially for long-life or regulated systems. How Engineers Are Solving It The teams navigating this best are taking a more strategic approach. They start by focusing on the parameters that actually matter in their circuit, such as noise, gm, leakage, and matching, rather than just looking for a “similar” part on paper. They also look to modern equivalents designed to replace legacy components, often improving consistency and long-term availability. In many cases, the replacement ends up being an upgrade rather than just a workaround. Validation is critical. Simulation helps, but real confidence comes from testing in-circuit, verifying biasing, and measuring actual performance. And importantly, they’re not doing it alone. Working directly with manufacturers who understand legacy components and application behavior can significantly reduce risk and speed up the process. A Shift in Mindset The most successful teams don’t just react to obsolescence. They use it as an opportunity to improve performance, reduce future supply risk, and strengthen their designs overall. It’s not just about replacing a part. It’s about making the design more robust long term. How We’re Helping Engineers Navigate This At Linear Systems, we work with engineers every day who are dealing with obsolete JFETs, hard-to-source components, and performance-sensitive designs. We help identify strong replacement options, provide cross reference guidance, supply samples for evaluation, and support real-world validation. The goal is simple: help you keep your design performing the way it should. Need Help with an Obsolete Part? If you’re dealing with a part that’s no longer available or becoming difficult to source, we’re happy to help. Drop the part number or application in the comments or message me directly and we’ll point you in the right direction. Quick Question What’s the biggest challenge you face with obsolete components? Finding a true replacement, maintaining performance, supply chain reliability, or avoiding redesign? #AnalogDesign #ElectronicsEngineering #Semiconductors #JFET #Obsolescence #HardwareEngineering #EE #ProductDesign #SupplyChain

Linear Systems is pleased to announce the release of a new SPICE model for the PAD Series low-leakage diode, developed by our engineering team. This model enables designers to simulate the SSTPAD10 in LTspice and other SPICE-compatible simulators, supporting faster circuit development and more accurate performance evaluation. The PAD Series of low-leakage diodes was designed for precision applications where minimizing leakage current and maintaining stable capacitance are critical. Its performance makes it well suited for sensitive analog circuits and high-impedance signal paths. 🔗 Explore the PAD Series Typical applications include: Precision instrumentation Low-noise analog front ends Protection circuits High-impedance signal paths Test and measurement systems The PAD Series offers controlled junction capacitance, low leakage characteristics, and stable breakdown performance, making it a reliable choice for both new designs and performance-critical applications. Providing SPICE models allows engineers to evaluate device behavior early in the design process and integrate Linear Systems components with greater confidence. We will continue expanding our SPICE model library to support additional Linear Systems devices. 📥 Download SPICE Model ( Link to SPICE model file ) 💬 Stay Connected Follow Linear Systems for new device releases, SPICE models, and application insights.

Purchase Directly from Linear Systems Linear Systems offers direct sales to customers as well as through our network of authorized distributors, each with its own unique benefits. Contact us at (510) 490-9160 or sales@linearsystems.com for assistance with price quotes, samples, custom part discussions, drawing evaluations, and valuable insights. Contact Us! Purchase Directly from Authorized Distributors Customers have the option to order through Linear Systems' authorized distributors, ensuring access to our high-quality parts worldwide. Some distributors provide additional services such as design support, product screening, and testing. Purchasing directly from Linear Systems, or through our authorized distributors guarantees you receive genuine components and exceptional support tailored to your needs. Global Distributors Below are our International Distributors, shipping to locations worldwide. Linear Systems' Authorized Distributor, Micross Linear Systems' Authorized Distributor, NAC Semi Linear Systems' Authorized Distributor, Trendsetter Electronics Linear Systems' Authorized Distributor, Mouser Electronics Linear Systems Authorized Distributor, DigiKey Electronics Regional Distributors Should you wish to order from a distributor nearer to your location, kindly consult the following list, as we have distributors located around the world. Italy Schurter Electronics S.p.A. Email info.it@schurter.com Phone # +39 02 3046 5311 Website Germany, Switzerland & Austria SEMITRON W. Röck GmbH Distribution + Testhaus Email sales@semitron.de Phone # +49 7742 800-10 Website United States Trendsetter Electronics Email sales@trendsetter.com Phone # (512) 310-8858 Website United States NAC Semi Email sales@nacsemi.com Phone # (727) 828-0187 Website Korea Unotel Co., Ltd. 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Linear Systems provides a wide range of JFET switches under its Improved Standard Products ® line of devices. We provide these components in an array of package types and make selections to specific electrical specifications upon request. JFET Switches Linear Systems provides a wide range of JFET switches under its Improved Standard Products ® line of devices. We provide these components in an array of package types and make selections to specific electrical specifications upon request. 2N/PN/SST4391 Series SINGLE, LOW NOISE, N-CHANNEL JFET SWITCH Read More 174DFN Series DFN PACKAGE, SINGLE P-CHANNEL JFET SWITCH Read More 2N5114 Series 2N5114 SERIES LOW ON-RESISTANCE, P-CHANNEL JFET SWITCH Read More 4391DFN Series DFN PACKAGE, SINGLE N-CHANNEL JFET SWITCH Read More LSJ/SST94 SINGLE P-CHANNEL JFET SWITCH Read More J/SST111 Series J111 SERIES LOW LEAKAGE, N-CHANNEL JFET SWITCH Read More J/SST174 Series SINGLE P-CHANNEL JFET SWITCH Read More 2N5018 Series 2N5018 SERIES LOW ON-RESISTANCE, P-CHANNEL JFET SWITCH Read More

Sample Boxes Sample Boxes DFN Sample Kit INCLUDES A SAMPLING OF PARTS OFFERED IN THE DFN PACKAGE Read More