# Questions tagged [jfet]

Junction Field Effect Transistor - A transistor whose channel is modulated by the application of an electric field that is the depletion region of a reversed biased diode that forms the gate electrode. Characteristic features of the device are low noise and low gate capacitance.

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### Common Source JFET amplifier input voltage

I want to compare to different formulas which stand for same parameter/value. Here is common source JFET amplifier circuit schematic: Here is the first formula which should apply in general to all ...
The output resistance of small signal model for common drain JFET amplifier equals $$\frac{1}{g_\text{m}} || R_{\text{ds(on)}} \parallel R_\text{S}$$ and since $$R_{\text{ds(on)}} =\frac{1}{g_\text{... 3answers 4k views ### Common Source JFET small signal equivalent circuit This circuit is equivalent to small-signal common source JFET amplifier: If you look at the input and output impedance you can see that Zin = R1 || R2 and Zout = rd || Rd || Rl. It can be seen from ... 1answer 362 views ### I/O Voltage of JFET Common Source with source degeneration For common source JFET (n-channel): Uin = Ugs (approximation for simplicity), but really Uin is a little bit lower because of input resistance, like so and Uout equals something like this: But how ... 1answer 5k views ### Bypass source capacitor JFET I know there were some changes applied to voltage amplification formula of BJT when "Ce" (emitter bypass capacitor) was connected to the circuit. How is it with JFET (MOSFET too) and its bypass ... 3answers 1k views ### What's the purpose of the diode at the JFET gate in this Hartley oscillator? This is something of a follow-up question to one I asked a few days back (Original JFET Hartley Question). Having made the changes suggested in the comments (i.e., changing Rd/R3 to 270 ohms, instead ... 0answers 279 views ### Problem distinguishing BJT from JFET I was testing few types of transistors on my newly acquired peak atlas pro and came across some N-channel depletion mode JFETs marked 2n3819. To my surprise the device indicated they are NPN BJTs. ... 0answers 637 views ### JFET transconductance vs. MOSFET transconductance JFET's n-channel highest transconductance (from datasheets) is marked as In theory, the same value is defined as that applies for n-channel JFET. I haven't found equation which defines MOSFET's ... 0answers 881 views ### JFET Different Output Characteristics for different Vgs,off Hi guys, I've been trying to design a simple amplifier with some gain. My first question is, why are there multiple output characteristic graphs (2 shown) for a single JFET? My first step in designing ... 1answer 524 views ### JFET Creating DC Offset In All-Pass Filter Output? Full disclosure, this is a circuit I've constructed as part of a lab at school, however this isn't a specific question I need to answer in the report, this is something I've observed and can't explain ... 3answers 1k views ### Matching JFETs for differential amplifier application How to choose a properly matched pair of JFETs for differential amplifier? Is it enough to measure their Idss? 0answers 356 views ### Photodiode JFET amplifier stage in pinch off? In the circuit below, it seems that the JFET is biased in a regime with very low current (pinched off?). With respect to most designs I came across, this one uses rather large source and drain ... 1answer 726 views ### How to measure / determine a FET's Vto (Vgs_off)? I have a bunch of FETs and i would like to select them / choose only those with -0.7 Vto. Is it an easy way to measure this parameter? Thanks 1answer 818 views ### NC JFET switch with only one voltage source [closed] The below circuit functions as a NC switch. At Vgs = 0V current flows through the channel of J1 (the JFET). When S is closed J1 will open and no current flows through the channel anymore. Right now ... 5answers 169 views ### Simple, low power way to buffer a 500mV threshold signal to an open collector output? I have a signal that is 0-500mV when low and 600-900mV when high. I'd like to buffer this signal to an open collector output. The output must withstand a maximum of 3.3V be capable of sinking 60uA. ... 2answers 100 views ### Diode with an enabler function I need to implement a diode, which only operates, when enabled by external signal. Specifications: When the enabling signal is off, there is no current irrespective of voltage (positive or negative, ... 1answer 790 views ### Shockley's Equation for JFET transistor in Proteus I'm trying to do a simulation using Proteus for the NJFET Transistor ... But when simulating the Shockley's Transfer equation i get a wrong curve And here is graph's properties 3answers 3k views ### Common Source JFET Amplifier I am trying to build a simple JFET common source amplifier to get about 5-10 times gain for a signal I have coming from a microphone with an amplifier already in it, from ADA Fruit, here I am working ... 3answers 136 views ### Is it possible to create a (depletion mode) MOSFET using only single type of semiconductor? If I understood JFET diagram correctly, the p-n junction is only used to isolate gate. Using same principle, would it be possible to construct a MOSFET with no junction at all, i. e. a single ... 2answers 700 views ### Understanding an N-JFET I am currently learning about FET transistors, and there is some things that I do not understand about an n-type JFET. I have two question about this transistor. Why is Vgs important and how do we ... 1answer 1k views ### How to correctly wire LF356 JFET Opamp as amplifier? I have a circuit in which a square wave with smaller amplitude should be amplified with an opamp. Before, I used a MAX492 which has G/B-product of 500 kHz. With this circuit I manage to easily amplify ... 1answer 461 views ### colpitts oscillator with jFET not working I decided to build a colpitts oscillator using a jFET (2N3819): It seems to work fine @ http://www.falstad.com/circuit/ but when i try to build this circuit it does not work, any ideas? Thank you ... 1answer 444 views ### Voltage follower with a pair of matched FETs I am studying for an exam and as a part of a question I have to explain biasing and operation of the voltage follower that uses two matched JFETs in the following arrangement: I am not sure that I ... 1answer 911 views ### Having trouble designing a JFET input stage in a Multistage Transistor Amp I've been given the task to design a multistage transistor amp. Specs given are: Overall voltage gain: 80 (min) to 100 (max) Input resistance no less than 1Mohm Voltage supplies: +-10V Achieve max ... 1answer 619 views ### Can this VCA bring output volume to zero? I'm working on a synthesizer and trying to keep the VCA simple. I'm also trying to avoid LM13700s, partly because I want this to run on one 9V batter. So I'm trying to make this design work: My CV ... 2answers 746 views ### Jfet as HV resistor I want a voltage controlled resistor for high voltages for a project I'm working on and using a common emitter/source transistor to shunt current into ground in order to get a desired voltage is not ... 2answers 660 views ### make a buffer balanced i am still new to electronic and i probably have a stupid question.. i am trying to build a buffer for a piezo microphone following the project on this site: http://www.scotthelmke.com/Mint-box-... 1answer 767 views ### What is the most commonly used transistor? Just a question about transistors from a rookie. I was wondering what kind of transistor is most commonly used? Bipolar transistors? JFET? MOSFET? 1answer 570 views ### JFET - Ceramic Resonator - Oscillator Phenomonom going in and out of oscillation An oscillator using a ceramic resonator is going in and out of oscillation. I have an oscillator circuit with a peculiar phenomonon. The oscillator does work (mostly). The “crystal” I am using ... 1answer 225 views ### JFET Amplifier Exersice I'm having a little confusion with a question on JFET amplifiers. This is the Q. You are required to design an audio amplifier using an n-channel JFET which has a pinch off voltage of -16V and a ... 1answer 1k views ### Transistor Based Wien Bridge Oscillator I've been studying the schematic for this RLC Bridge from Heathkit (IB-5281). The full pdf can be found here (search for the part number): http://www.vintage-radio.info/heathkit. The circuit ... 1answer 147 views ### Currents confusion in a JFET datasheet I am analyzing a JFET. The datasheet has both information about the currents Igss and the maximum of Ig. I know that the Igss is a the reverse current in the PN junction but I can't explain myself ... 1answer 99 views ### The characteristics of a JFET I understand that when Vgs = 0, and there is a steady current Vds, there is a pinching shaped depletion region and so on. But what I have a confusion with is when Vgs > 0 or Vgs < 0. The book ... 1answer 6k views ### Transfer characteristic of JFET I read that in transfer characteristics of JFET, Vds is kept constant and Vgs is varied. But when Vp for any device is constant and Vds is also constant then even Vgs should be constant. 1answer 636 views ### In an n-channel JFET, why isn't the formation of depletion layer symmetrical? When a reverse bias voltage is applied between the gate and the source, depletion layer is formed between the p-type and n-type materials in the JFET. My question is why isn't it symmetrical? Why does ... 3answers 838 views ### Understanding p JFET I would like to make sure that I understood p JFET (https://electronics.stackexchange.com/a/97350/78253) right: With SWitch1 in its current position, there is voltage at the gate of the J1 p JFET, ... 1answer 142 views ### Actively biased JFET Amplifier simulate this circuit – Schematic created using CircuitLab Its just the basic diagram (the actual circuit is a low noise amplifier at 5.5GHz).It does work very correctly.In this circuit the BJT ... 1answer 1k views ### JFET Audio switch, does not work in simulation? This is a circuit I've found online and apparently it is taken from the very rare audio book by National semi. The circuit is used to switch a signal on and off at a transition time that the user sets ... 2answers 706 views ### Depletion P-channel JFET that's saturated at $V_{GS}=0V$ Is there any depletion-mode P-channel JFET that is saturated at $V_{GS} = 0V$? 1answer 2k views ### Transfer characteristic of p-channel JFET Considering the output characteristic of the n channel JFET, can we somehow obtain the same characteristic only for the p-channel type of this transistor? In R.Jaeger's book about microelectronics ... 2answers 3k views ### JFET's Understanding - Voltage Controlled Resistor If the JFET is supplied from a constant current source (5ma flowing Source-Drain) Will changing the Vgs voltage do anything? This Image for reference: Another graph of a 2N5457 taken for the ... 2answers 567 views ### FETs transfer characteristics in 4 quadrants Recently I was given a following problem on the test: Usually, transfer characteristic (Id(Vgs)@Vds) of JFET and MOSFET is plotted in the 2 quadrants. Plot it in all 4. After the test we were not ... 4answers 586 views ### JFET in place of digipot for gain control? I'm hoping to build a sound sensor using this schematic (http://cdn.sparkfun.com/datasheets/Sensors/Sound/sound-detector.pdf) To programmatically adjust the gain, I could use a digipot. My (naive) ... 1answer 2k views ### Computing K parameter for Mosfet/JFet/ I am writing a simple simulator for Mosfet and JFet. The equations governing these involve the important parameter "K". But, the data sheets normally do not provide the value of parameter K. So, I ... 3answers 841 views ### jfet preamp output attenuated and clipped on bottom rail when connected to codec I am currently working on an embedded audio processing system for electric guitar. I have constructed two JFET preamps (left and right channels) based on the j201 transistor using the common source ... 2answers 3k views ### Advantages of depletion mode FET devices over enhancement MOSFETs I've grown the impression that JFETs and depletion mode MOSFETs are not used very much nowadays, especially in new designs. I know that they need different bias networks, especially as discrete ... 2answers 1k views ### cirrus/wolfson wm8731 - Connecting Analog Input to Codec I am currently working on an embedded audio processor project based on the stm32f4discovery board and the wm8731 codec from cirrus/wolfson. I was wondering if anyone here is familiar with the codec ... 2answers 2k views ### Would this JFET+op-amp circuit work? This is Figure 9-3(b) from Motchenbacher - Low-Noise Electronic System Design, so I would expect it to work, but I don't understand it: The addition of a discrete common-source stage at the input ... 1answer 2k views ### Need help finding the drain current of a jfet I have this simple dc jfet circuit (homework): First of all I had to find the values of the drain and source resistors given the data above, this was pretty simple and I got:$$R_D=4k\Omega R_S=...
Hi im having some trouble with knowing how to perform calculations for $I_D$ in a simple JFET where it is biased by means of a voltage divider. I understand that use of the equation: I_D = I_{...