< Back What is a JFET? Linear Systems May 30, 2024 JFETs are three-terminal semiconductor devices that can be used as electronically controlled switches or resistors, or to build amplifiers. Linear Systems JFET (Junction Field-Effect Transistor) amplifiers are known for their exceptional performance in low-noise, high-input impedance applications. These amplifiers are particularly valued in audio, instrumentation, and signal processing systems due to their ability to amplify weak signals without adding significant noise. Dual JFET amplifiers incorporate two JFETs in a single package, which offers matched characteristics and improved thermal stability. This configuration enhances the performance and reliability of circuits that require closely matched transistors, simplifying the design and reducing component count. Such amplifiers find extensive use in differential amplifiers and other precision analog circuits, making them indispensable in high-fidelity audio equipment and sensitive measurement devices. JFET Basics JFETs are three-terminal semiconductor devices with a gate, source, and drain. They belong to the family of field-effect transistors (FETs), where the flow of current is controlled by an electric field applied to the device's gate terminal. In contrast to bipolar junction transistors (BJTs), which use a current-controlled base to control the collector-emitter current, JFETs utilize a voltage-controlled gate to regulate the source-drain current. This fundamental difference is what makes JFETs superior in high-impedance applications as they draw very little gate current, resulting in minimal loading and noise contributions. Common Source Amplifier The most widely used configuration for amplifying signals using a JFET is the common source (CS) amplifier. As the name suggests, the input signal is applied at the device's gate terminal and amplified output is obtained at its drain. The source terminal is common to both input and output circuits, hence the name. The CS amplifier offers high voltage gain, excellent linearity and good frequency response over a wide range. It also provides high input impedance and low output impedance, making it suitable for driving loads with varying impedances. Advantages of JFETs High Input Impedance: Because the gate is isolated from the source-drain path by a reverse-biased PN junction, JFETs have very high input impedance compared to BJTs or MOSFETs. This allows them to be used in high-impedance circuits without causing significant loading effects. Low Noise: Due to their low gate current and minimal internal resistance, JFETs exhibit very low noise performance, making them ideal for use in sensitive audio equipment and measurement devices. Good Linearity: The transconductance (gm) of a JFET is relatively constant over a wide range of input voltages, resulting in good linearity and low distortion compared to BJTs or MOSFETs. Simple Biasing: Unlike BJTs which require precise base biasing and MOSFETs which need complex circuitry for gate biasing, JFETs can be easily biased using a simple resistor or potentiometer. Reverse Bias Protection: The reverse-biased PN junction in the JFET acts as a natural diode, providing reverse bias protection and preventing damage to the device if the input voltage exceeds the specified limit. Applications of JFETs JFETs find applications in various electronic circuits such as: Low-Noise Amplifiers: Due to their low noise performance, JFETs are commonly used in audio amplifiers, radio receivers, and other sensitive applications where noise can be a major issue. Switching Circuits: JFETs can be used as simple on-off switches by connecting the gate to ground (for N-channel) or to the supply voltage (for P-channel) to control the flow of current between source and drain. Voltage-controlled Resistors : By varying the gate voltage, a JFET can be used as a variable resistor in circuits such as oscillators and filters. Sample-and-Hold Circuits: The high input impedance of JFETs makes them suitable for use in sample-and-hold circuits where the input voltage needs to be held constant for a short period of time. Constant Current Sources: JFETs can also be used as simple constant current sources, where the output current remains nearly constant despite changes in input voltage or load resistance. Other applications include use in high-frequency circuits, chopper amplifiers, and instrumentation equipment. With advancements in technology, JFETs are being increasingly replaced by other types of transistors such as MOSFETs. However, they still hold importance in certain specialized applications due to their unique characteristics and simplicity in biasing and operation. Conclusion JFETs are versatile electronic devices with numerous advantages over other types of transistors. These include high input impedance, low noise performance, and simplicity in biasing. They find widespread use in various applications such as amplifiers, switching circuits, voltage-controlled resistors, sample-and-hold circuits, and constant current sources. Despite being gradually replaced by other transistor types, JFETs still hold importance in certain specialized applications and continue to be an essential component in the field of electronics. With ongoing research and development, we can expect to see further advancements and improvements in JFET technology. These small but powerful devices will continue to play a significant role in shaping the electronic industry. So, it is important for any electronics enthusiast or professional to have a thorough understanding of the working principles and applications of JFETs in order to utilize them effectively in their circuit designs. With their versatile characteristics and unique advantages, JFETs have undoubtedly played a crucial role in the development of modern electronic systems and will continue to do so in the future. So next time you come across a JFET, remember their importance and versatility in the world of electronics.

< Back Testing Capability Linear Systems Mar 17, 2023 New Low-Noise Semiconductor Testing Capability FREMONT, Calif., April 11, 2019 /PRNewswire/ -- Linear Integrated Systems, Inc. (Linear Systems) will be unveiling its large-scale sub-nanovolt parts testing capability at the 23rd Annual Conference and Exhibition for Components for Military & Space Electronics (CMSE) in Los Angeles. This testing capability enables individual screening of small-signal discrete components to levels below a billionth of a volt (nV/√Hz) of noise in quantities up to tens of thousands of parts. Linear Systems created this capability in response to a U.S. defense program requirement and is now providing ultra-low-noise-screened parts to other customers. "Small-signal discrete components can help create the lowest noise signal chains possible and that's what our customers have been demanding," said Timothy S. McCune. "This sub-nanovolt testing capability enables us to provide production-line quantities of parts guaranteed to meet specific noise levels. No other company has this capability." Linear Systems will be available to discuss this capability and its line of precision small-signal discrete components at the 23rd Annual Conference and Exhibition for Components for Military & Space Electronics (CMSE) to be held at the Four Points by Sheraton (LAX), Los Angeles on April 16-18. CMSE is the premier event focused on the design, reliability, and application of electronic components for use in avionics aerospace, military & commercial space systems. The conference provides access to more than 30 technical presentations by industry leaders, focused on advanced packaging of ICs, passive components, and a number of other topics critical to components used in high reliability military and aerospace systems. Linear Systems specializes in the development and manufacture of precision, ultra-low-noise small-signal discrete components. Its parts, such as the LSK389 and LSK489, are used in highly demanding sensor systems ranging from the Large-Scale Synoptic Telescope to piezoelectric devices to sonobuoys. These parts also provide the front-end amplification for high-end test and measurement, medical and audio equipment. Linear Systems is a full-service, privately-held, designer and manufacturer of small-signal discrete semiconductors established in 1987. The Fremont, CA-based company was founded by John H. Hall, co-founder of Intersil and founder of Micro Power Systems. Linear Systems' product line consists of: Ultra-Low-Noise N-Channel and P-Channel Dual and Single JFETs, High-Speed Lateral DMOS Switches, Bipolar Transistors, BIFET Amplifiers, Current-Regulating Diodes, Low-Leakage Diodes, MOSFETs, PhotoFETS, and Voltage Controlled Resistors. Data sheets, applications notes, SPICE models and other information can be downloaded at linearsystems.com . For more information about Linear Systems please contact Ms. Laura Madonna at laura@linearsystems.com . For customer service, please contact Linear Systems at sales@linearsystems.com or call (510) 490-9160. SOURCE Linear Integrated Systems Related Links www.linearsystems.com

Linear Systems designs and manufactures the highest-performance line of monolithic dual JFETs in the industry. Contact us for a quote! Back LS830 Series ULTRA-LOW LEAKAGE, LOW DRIFT, MONOLITHIC DUAL N-CHANNEL JFET The LS830 Series of Ultra-Low Leakage, Low Drift, Monolithic Dual N-Channel JFETs is a pin-for-pin replacement for the Fairchild, Motorola, National and Siliconix-Vishay part series. Available in the TO-71 6L, TO-78 6L, PDIP 8L and SOIC 8L RoHS package, as well as bare die. Advanced screening options are available for our diverse product lineup, featuring JFETS, Bipolar transistors, MOSFETs, current regulators, and Diodes. Our special screening covers all the parameters listed in the standard datasheet, including comprehensive package pin-out. Connect with our experienced technical team to discuss your specific needs and tailor your requirements—email us at support@linearsystems.com or call (510) 490-9160. MOQ applies to these specialized services. Ordering Information Below are the options you have when ordering this part series: LS830 TO-71 6L RoHS LS831 TO-71 6L RoHS LS832 TO-71 6L RoHS LS833 TO-71 6L RoHS LS830 TO-78 6L RoHS LS831 TO-78 6L RoHS LS832 TO-78 6L RoHS LS833 TO-78 6L RoHS LS830 PDIP 8L RoHS LS831 PDIP 8L RoHS LS832 PDIP 8L RoHS LS833 PDIP 8L RoHS LS830 SOIC 8L RoHS LS831 SOIC 8L RoHS LS832 SOIC 8L RoHS LS833 SOIC 8L RoHS LS831 Die LS832 Die LS833 Die Datasheet Spice Model Application Notes

Linear Systems designs and manufactures the highest-performance line of monolithic dual JFETs in the industry. Contact us for a quote! Back SST/U421 Series LOW LEAKAGE, LOW DRIFT, MONOLITHIC DUAL, N-CHANNEL JFET The SST/U421 Series Low-Noise, Low-Drift, Monolithic Dual N-Channel JFET Amplifier is designed for a broad spectrum of precision instrumentation and sensor applications. This series is offered in TO-71 6L, TO-78 7L, PDIP 8L, and SOIC 8L RoHS-compliant packages, as well as in die form. Advanced screening options are available for our diverse product lineup, featuring JFETS, Bipolar transistors, MOSFETs, current regulators, and Diodes. Our special screening covers all the parameters listed in the standard datasheet, including comprehensive package pin-out. Connect with our experienced technical team to discuss your specific needs and tailor your requirements—email us at support@linearsystems.com or call (510) 490-9160. MOQ applies to these specialized services. Ordering Information The following options are available for ordering this part series: U421 TO-71 6L RoHS U422 TO-71 6L RoHS U423 TO-71 6L RoHS U424 TO-71 6L RoHS U425 TO-71 6L RoHS U426 TO-71 6L RoHS U421 TO-78 7L RoHS U422 TO-78 7L RoHS U423 TO-78 7L RoHS U424 TO-78 7L RoHS U425 TO-78 7L RoHS U426 TO-78 7L RoHS SST421 SOIC 8L RoHS SST422 SOIC 8L RoHS SST423 SOIC 8L RoHS SST424 SOIC 8L RoHS SST425 SOIC 8L RoHS SST426 SOIC 8L RoHS U421 Die U422 Die U423 Die U424 Die U425 Die U426 Die Datasheet Spice Model Application Notes

LOG CONFORMANCE, MONOLITHIC DUAL, PNP TRANSISTOR < Back LS358 LOG CONFORMANCE, MONOLITHIC DUAL, PNP TRANSISTOR The LS358 Log Conformance, Monolithic Dual, PNP Transistor is a direct replacement for Micro Power Systems MP358 Series. It is ideal for Log Conformance, Transistor Amplifier & Switching Applications. It is available the in TO-71 6L RoHS, TO-78 6L RoHS, PDIP 8L ROHS and SOIC 8L RoHS package, as well as bare die. Advanced screening options are available for our diverse product lineup, featuring JFETS, Bipolar transistors, MOSFETs, current regulators, and Diodes. Our special screening covers all the parameters listed in the standard datasheet, including comprehensive package pin-out. Connect with our experienced technical team to discuss your specific needs and tailor your requirements—email us at support@linearsystems.com or call (510) 490-9160. MOQ applies to these specialized services. Ordering Information Below are the options you have when ordering this part series: LS358 TO-71 6L RoHS LS358 TO-78 6L RoHS LS358 PDIP 8L RoHS LS358 SOIC 8L RoHS LS358 Die Datasheet Spice Model Application Notes

SINGLE, LOW-NOISE, LOW-LEAKAGE, N-CHANNEL JFET AMPLIFIERS < Back LSK189 SINGLE, LOW-NOISE, LOW-LEAKAGE, N-CHANNEL JFET AMPLIFIERS The LSK189 Single, Low Noise, Low Leakage, N-Channel JFET Amplifiers is a single version of LSK489 Series. It is ideal for Ultra Low Noise Audio/Acoustic Applications. Available in TO-92 3L ROoHS, SOT-23 3L RoHS package, as well as in die form. Advanced screening options are available for our diverse product lineup, featuring JFETS, Bipolar transistors, MOSFETs, current regulators, and Diodes. Our special screening covers all the parameters listed in the standard datasheet, including comprehensive package pin-out. Connect with our experienced technical team to discuss your specific needs and tailor your requirements—email us at support@linearsystems.com or call (510) 490-9160. MOQ applies to these specialized services. Ordering Information Below are the options you have when ordering this part series: LSK189 TO-92 3L RoHS LSK189 SOT-23 3L RoHS LSK189 Die Datasheet Spice Model Application Notes

SINGLE P-CHANNEL JFET SWITCH < Back J/SST174 Series SINGLE P-CHANNEL JFET SWITCH The J/SST174 Series Low On-Resistance, P-Channel JFET Switch is a direct replacement for the Fairchild and Siliconix-Vishay part series. It is ideal for low resistance, low operating current switching applications. Available in the DFN 8L RoHS, TO-92 3L RoHS and SOT-23 3L RoHS package, as well as in die form. Advanced screening options are available for our diverse product lineup, featuring JFETS, Bipolar transistors, MOSFETs, current regulators, and Diodes. Our special screening covers all the parameters listed in the standard datasheet, including comprehensive package pin-out. Connect with our experienced technical team to discuss your specific needs and tailor your requirements—email us at support@linearsystems.com or call (510) 490-9160. MOQ applies to these specialized services. Ordering Information Below are the options you have when ordering this part series: 174DFN 8L RoHS 175DFN 8L RoHS 176DFN 8L RoHS 177DFN 8L RoHS J174 TO-92 3L RoHS J175 TO-92 3L RoHS J176 TO-92 3L RoHS J177 TO-92 3L RoHS SST174 SOT-23 3L RoHS SST175 SOT-23 3L RoHS SST176 SOT-23 3L RoHS SST177 SOT-23 3L RoHS J174 Die J175 Die J176 Die J177 Die Datasheet Spice Model Application Notes

< Back LSK389 App Note Introduction The LSK389 is the industry’s lowest noise Dual N-Channel JFET, 100% tested, guaranteed to meet 1/f and broadband noise specifications, while eliminating burst (RTN or popcorn) noise entirely. The product displays high transconductance and very good matching. It is the JFET of choice for low noise applications, especially those requiring a differential amplifier input stage. Read More

< Back FETching Discrete Amplifier Introduction Low-noise amplifiers for photodiode, piezoelectric, and other instrumentation applications typically call for circuit parameters such as extremely high input impedance, low 1/f noise, or subpicoamp bias currents that cannot be met with available integrated products. This article discusses the requirements and challenges of designing a low-noise amplifier using discrete components, with particular emphasis on input-referred noise and offset voltage trimming. Read More

The Linear Systems family of high speed DMOS switches is designed to handle a wide range of video, fast ATE, telecom and other analog switching applications. DMOS High Speed Switches The Linear Systems family of DMOS devices is designed to handle a wide range of video, fast ATE, telecom and other analog switching applications. These components are capable of ultrafast switching speeds (tr = 1 ns, tOFF = 3 ns) and excellent transient response. Thanks to reduced parasitic capacitances, our DMOS can handle wideband signals with high off-isolation and minimum crosstalk. SD/SST210 Series SD/SST210 SINGLE, HIGH SPEED N-CHANNEL LATERAL DMOS FET SWITCH Read More SD/SST211 Series SD211DE SINGLE, HIGH-SPEED N-CHANNEL LATERAL DMOS FET SWITCH Read More SD5000 Series SD5000 SERIES QUAD, HIGH SPEED N-CHANNEL, LATERAL DMOS FET SWITCH Read More

HIGH VOLTAGE, SUPER BETA, MONOLITHIC DUAL, NPN TRANSISTOR < Back LS301 Series HIGH VOLTAGE, SUPER BETA, MONOLITHIC DUAL, NPN TRANSISTOR The LS301 Series High Voltage, Super Beta, Monolithic Dual, NPN Transistor is a direct replacement for the Micro Power Systems MP301, MP302, MP303 Series. It is ideal for Small Signal Transistors, Super Beta, Amplifier & Switching Applications. It is available the in TO-71 6L RoHS, TO-78 6L RoHS, PDIP 8L ROHS and SOIC 8L RoHS package, as well as bare die. Advanced screening options are available for our diverse product lineup, featuring JFETS, Bipolar transistors, MOSFETs, current regulators, and Diodes. Our special screening covers all the parameters listed in the standard datasheet, including comprehensive package pin-out. Connect with our experienced technical team to discuss your specific needs and tailor your requirements—email us at support@linearsystems.com or call (510) 490-9160. MOQ applies to these specialized services. Ordering Information Below are the options you have when ordering this part series: LS301 TO-71 6L RoHS LS302 TO-71 6L RoHS LS303 TO-71 6L RoHS LS301 TO-78 6L RoHS LS302 TO-78 6L RoHS LS303 TO-78 6L RoHS LS301 PDIP 8L RoHS LS302 PDIP 8L RoHS LS303 PDIP 8L RoHS LS301 SOIC 8L RoHS LS302 SOIC 8L RoHS LS303 SOIC 8L RoHS LS301 Die LS302 Die LS303 Die Datasheet Spice Model Application Notes

TIGHT MATCHING, MONOLITHIC DUAL, PNP TRANSISTOR < Back LS350 Series TIGHT MATCHING, MONOLITHIC DUAL, PNP TRANSISTOR Previous Next