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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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

3 days ago

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

4 days ago

SD5400 Now Available in QFN 16L Package

More design flexibility. Less board space. Linear Systems has expanded the SD5400 quad analog switch family with a new compact 3 × 3 mm QFN-16 package—giving designers another surface-mount option for space-constrained, high-speed analog applications. The SD5400 integrates four independent, bidirectional SPST switches on a common substrate. Built using our proprietary lateral DMOS process, it combines low on-resistance, low interelectrode capacitance and exceptionally fast sw

5 days ago

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

JFET Design Spotlight: A case for Paralleling JFETs for lower noise

What happens when you rethink low-noise amplifier design from a clean sheet? This design explores paralleling LSK389 JFETs to push noise even lower. “Things happen while throwing out historical habits in favor of a clean piece of paper. Differential Amplifiers, being relatively commonplace in analog circuit design, have traditionally followed familiar circuit practices regarding noise. For this discussion JFETs are of interest though Bipolar parts similarly apply. Front end n

Sep 16

JFET Design Spotlight: High-Speed Sonar Front End for Aquatic Imaging

This week’s Design Spotlight takes us into a sonar application proposed for multi-channel aquatic imaging. The design uses a dual matched JFET front end to meet the sensor’s differential loading requirements while providing the low-noise, high-speed performance needed for downstream A/D conversion. “Just another JFET circuit that was composed and built for a Sonar application, proposed to be used in multiple for aquatic imaging. One of the requirements was a loading impedance

Sep 4

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

Design Spotlight: JFET Current Limiters for the Masses

Bidirectional current limiting presents an interesting analog design challenge—and the unique structure of a JFET offers some creative ways to solve it. In this Design Spotlight, three approaches are explored, from dual-device configurations to a particularly simple single-JFET solution that takes advantage of the interchangeability of the Source and Drain. The designs highlight differences in crossover behavior, current stability, and voltage compliance, including considerat

Aug 19

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

⚡ FET Design Spotlight: Electron Beam Circuit Protection with PAD Diodes

High-voltage electron beam systems demand precision—and protecting sensitive measurement circuitry is critical to maintaining accuracy and minimizing costly downtime. In this latest FET Design Spotlight, we look at how Linear Systems PAD Diodes have provided reliable circuit protection in electron beam applications for more than 35 years. Electron Beam Circuit Protection by PAD Diodes "High-voltage applications happen to be a difficult place to involve sensitive measurement a

Aug 12

Linear Systems Learning Series: How to Read a JFET Datasheet

A JFET datasheet contains dozens of electrical characteristics, graphs, and performance curves—but which specifications matter most? The answer depends on your application. A designer building a low-noise microphone preamplifier may prioritize different parameters than someone designing a current source or a high-impedance sensor interface. Understanding what each specification represents is the first step in selecting the right device. 1. Noise Voltage For precision analog f

Aug 6

Linear Systems Learning Series: Understanding 1/f Noise: Why Low-Frequency Noise Matters

Not all noise is created equal. When engineers compare low-noise devices, they often focus on the 1 kHz noise specification. While that's an important benchmark, it doesn't tell the whole story. At lower frequencies, many semiconductor devices exhibit 1/f noise, also known as flicker noise. As frequency decreases, this noise increases, making it especially important in applications that measure slow-changing or very small signals. Examples include: Precision instrumentation M

Jul 28

JFET Design Spotlight: Phantom-Powered Piezo Preamplifier Design

Another glimpse into the creative mind of analog designer Kirkwood Rough. "‘No batteries allowed on this instrument,’ was the statement from the luthier. So, a phantom-powered preamp needed to be configured using a standard guitar cable. 'Nothing special.' First, the piezo loading had to be minimal so its charge capacity would not run out and sound 'buzzy' on the low end. Second, the piezo needed to be sensed differentially and therefore shielded. Third, no batteries could be

Jul 28

Why Matching Matters in Dual JFETs: Improving Precision Differential Amplifier Performance

When designing a precision differential amplifier, low noise is only part of the equation. The two input transistors must behave as similarly as possible. Even small differences in electrical characteristics can introduce input offset voltage, reduce common-mode rejection (CMRR), increase temperature drift, and ultimately limit the accuracy of the entire circuit. That's why device matching is so important. Rather than pairing two individual transistors, many engineers choose

Jul 22

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

JFET Design Spotlight: Crafting the Perfect Bass Overdrive

We're always fascinated by the way Kirkwood Rough approaches analog circuit design. Here's another one of his design stories. "Sometimes a sound gets a grip on your senses and that happened to be the Bass lines from Moulin Rouge. They were Fat, rich, percussive and Smooth with a high octave layered presence. That started a design process that ended up being the LadyMarmalade™ effect. It had to enhance even ordered harmonics without a sharp clipping effect, even when overdrive

Jul 16

🔦 Product Spotlight: SST211 / SD211DE Series

When switching speed and signal integrity matter, every nanosecond counts. The SST211/SD211DE Series of N-channel lateral DMOS switches is designed for high-speed, low-glitch analog switching in demanding applications where low capacitance and fast response are critical. Key Features ⚡ 1 ns maximum turn-on time ⚡ Ultra-low 0.2 pF reverse transfer capacitance (Crss) ⚡ Low rDS(on) ⚡ Low turn-on threshold voltage ⚡ Integrated Zener ESD protection ⚡ Available in TO-72 4-Lead (SD2

Jul 10

The Tiny Component Helping Power Next-Generation AI Servers

Artificial intelligence is transforming nearly every industry, and the spotlight is often on powerful GPUs, advanced processors, and sophisticated software. But behind every AI server is an equally important layer of technology that rarely gets the attention it deserves: precision analog electronics. From routing high-speed signals to monitoring critical system functions, analog components help ensure AI servers operate with the speed, reliability, and accuracy today's data c

Jul 8

Why Engineers Are Still Using Discrete JFETs

Integrated circuits continue to advance, but many of the highest-performance analog front ends still begin with a discrete JFET. Why? Because when you're trying to capture extremely weak signals, the input stage often determines the performance of the entire system. Engineers continue to choose discrete JFETs for applications requiring: Ultra-low noise High input impedance Low input capacitance Excellent linearity Whether designing photodiode amplifiers, hydrophone preamplifi

Jun 25