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Engineering Insights from Linear Systems
For nearly four decades, Linear Systems has specialized in high-performance discrete semiconductors for demanding analog applications. Today, we're putting that experience to work beyond the devices themselves by sharing practical technical resources for the engineering community.
Explore the Linear Systems Learning Series, JFET circuit and design spotlights, application insights, technical articles, new product releases, and semiconductor industry updates—all focused on helping engineers solve real-world analog design challenges.
You'll also find the latest on our ultra-low-noise JFETs, lateral DMOS switches, bipolar transistors, BIFETs, current regulators, low-leakage diodes, and other precision semiconductor technologies.
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Linear Systems Learning Series: Understanding Gate Leakage
When engineers evaluate a JFET, specifications such as noise, transconductance, input capacitance, and IDSS often receive most of the attention. But in high-impedance circuits, another specification can become extremely important: gate leakage current. JFET gate current may be extraordinarily small, often measured in picoamps or nanoamps. But when that tiny current interacts with a very high source impedance, it can create a measurable error. Understanding gate leakage, and t
3 days ago
BEYOND THE DATASHEET: HOW JFET NOISE IS MEASURED—AND WHY TESTING MATTERS
A JFET datasheet may list an impressively low voltage-noise number—but how was that number measured, at what frequency, and does it represent a typical value or a guaranteed maximum? Those details matter. At nanovolt-per-root-hertz levels, the measurement system, test conditions and specification method can significantly influence the result. Understanding what sits behind the published number helps engineers make more meaningful comparisons between devices. WHAT DOES A JFET
Sep 25
JFET Design Spotlight: Negative Resistance in a Semiconductor
JFETs are commonly used in amplifiers, current sources, variable resistors, and oscillators, but sometimes the most interesting designs come from using them in ways you wouldn’t normally expect. This week’s Design Spotlight explores one of those “odd uses”: creating a negative resistance effect with complementary N-channel and P-channel JFETs. “Use of JFETs in typical applications range from amplifiers to variable resistors and oscillators, among many other applications, bu
Sep 24
JFET Design Spotlight: Another Variation of a High Z Preamp for Low Level Piezo Sensing
This week’s Design Spotlight is another great example of how JFETs and precision discrete components can come together to solve demanding analog design challenges. “Though there was another Piezo sensor earlier, this one has a bit more gain and a design bandwidth of 1.3 MHz. This circuit uses, as you’d expect, a low noise LSK389 differential JFET pair cascoded by Q1 & Q2 into a Widlar style current mirror. The LS310 transistor pair maintains constant voltage, low impedance
Sep 18
Linear Systems Learning Series: Understanding VGS(off) - What JFET Cutoff Voltage Really Means
Last week, we looked at IDSS—the drain current a JFET conducts when VGS = 0 V under specified conditions. This week, we're looking at the other end of the JFET's transfer characteristic: VGS(off), or gate-to-source cutoff voltage. If IDSS helps tell us where the JFET starts at zero gate bias, VGS(off) helps define the point at which the channel is essentially turned off. Understanding both gives engineers a much better picture of how a JFET responds to gate voltage—and how to
Sep 2
Linear Systems Learning Series Understanding: IDSS - What Drain Current Tells You About a JFET
Last week, we took a closer look at transconductance (gfs) and what it tells engineers about how strongly a JFET responds to a change in gate voltage. This week, we're continuing our look at key JFET datasheet parameters with another specification you'll see frequently: IDSS — Drain-to-Source Saturation Current. IDSS is one of the fundamental characteristics of a JFET, and understanding it is important when selecting a device and establishing its operating point. Put simply:
Aug 26
Linear Systems Learning Series: Understanding Transconductance: What gfs Tells You About a JFET
Last week, we looked at how to read a JFET datasheet and the key specifications engineers should evaluate when selecting a device. This week, we're taking a closer look at one of those parameters: transconductance (gfs). Transconductance is an important JFET characteristic because it tells us how effectively the device converts a change in gate-to-source voltage into a change in drain current. Put simply: How strongly does the JFET respond to a change at its input? What Is Tr
Aug 18
Beyond Low Noise: Why Input Capacitance Matters
Last week we discussed why engineers continue to choose discrete JFETs for precision analog designs. But selecting the right JFET involves more than comparing noise specifications. For high-impedance applications such as photodiodes, hydrophones, piezoelectric sensors, condenser microphones, and precision instrumentation, input capacitance can have a significant impact on circuit performance. Higher input capacitance can reduce bandwidth, increase signal loading, and make com
Jul 16
Improving Bandwidth in Photodiode Amplifiers with the LSK489 Ultra-Low Noise, Low Capacitance Dual JFET
Designing high-speed photodiode and sensor front ends often comes down to one limiting factor: input capacitance. Even when noise performance is optimized, excess capacitance at the input can restrict bandwidth, slow response time, and introduce distortion. For engineers working with precision optical or sensor signals, this creates a constant tradeoff between speed, stability, and complexity. In photodiode and high-impedance sensor circuits, total input capacitance directly
Apr 15
A Radio Frequency RMS Metering Circuit
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 temp
Apr 9
Struggling with Obsolete Parts? How Engineers Are Solving It
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 c
Apr 6
🔧 FET Friday: Ultra-Low Noise Designs with the LSK389
Looking to push the limits of low-noise performance? This application note explores advanced amplifier techniques using Linear Systems’...
Jun 13, 2025
Enhancing Voltage-Controlled Resistor (VCR) Performance with Buffered Global Feedback Using N-Channel JFETs
In precision analog applications, minimizing distortion while maintaining frequency response is essential when implementing a...
May 8, 2025
Exploring the Reversed Sziklai Pair
🔬 Exploring the Reversed Sziklai Pair 🔍 Check out this clever hybrid design that flips the script on traditional amplifier topology! ...
Apr 11, 2025
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