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157 Threads found on Fet Amplifier
The gate has to be held slightly negative in the cases I have seen, and the right answer varies with temperature, "make" tolerances and so on. One approach I have seen is to sense the voltage across the drain impedance and servo that through a poor-boy op amp to maintain a constant drain current (against an external reference). Of course if the l
I am looking for Vfet 2SJ18, 2SK60 for an old SONY amplifier. It is not available locally. Please suggest equivalent for 2SJ18 and 2SK60.
I think the diagram you show is quite primitive. The antenna will influence the transmitted frequency. It would be better to use a buffer transistor at the output of the oscillator (repeater on emitter maybe). I don't think you need to change from bipolar to fet. The TV spectrum is very large, from 48 MHz to over 800 MHz. What channel do you want t
Hi all, I have designed an amplifier and stabilised the fet unconditionally and checked the K factor across wide band using AWR microwave office and PA was stable across the band. However, when I extracted the EM structures of the matching networks and checked the K factor again, I found out that K factor is below zero at som
Hi, I am supposed to design a transmitter for my project. I have already pretty much finished the VCO and Power amplifier and now need to build the Mixer. My professor said a Passive Quad-fet would be a good architecture to build. But I am confused on how the schematic for this looks. I keep finding different circuits that contradict one another. I
OTAs are simple, easy to compensate (shunt C on output) and easy to slap around with their current limited output (e.g. soft start, current limit functions). Their gain tanks with any resistive load, but internal to a CMOS IC there may be none (just C pretty much). LDOs operate the pass fet in linear region -when low supply headroom- but this is
If you use a very high negative feedback resistance then the stray capacitance at the (-) input causes a phase shift that might cause oscillation. If you need an opamp with a very high input impedance then use one with fet inputs. Many are available.
PMOS LDOs always have a hard time with HF PSRR, any groundward jerk on the pass fet gate is directly amplified (common source amplifier). In normal CMOS techologies ground parasitics are pervasive. You may need to look at compensation schemes (like, Miller makes it worse as any drain jerk - which would include + supply movement, relative to the f
voltage divider Jfet common source amplifier with output voltage biased at the half of supply voltage. what does the above sentence mean???
The LM195 was basically a NPN common-emitter voltage amplifier with a threshold of 0.6V and an NPN Darlington Emitter Follower. It's performance was like a fet with a threshold of Vth=0.6V witha n RdsON of ~1Ω but with an extra diode drop on the output. The advantage of the LM195 was that it was rugged with current limit protection but not
Hello, Does anyone know which is the characteristic that defines an operational amplifier at one of the tree catategories (BJT, fet, CMOC)? Is the type of tranzistors that have on his input or in output or in both (in and out)?
Hey All! :) I am working on an Hfet. I need to find the Bias points (Vgs and Vds) for this Hfet using ADS. I have simulated the IV curves. Further, How should I conclude my Bias points from The IV curves? I have attached a screenshot of the Data display. Please take a look and Help me!!
In most applications of high power balanced amplifiers using 2 fetS (or MOSfets) the gates are biased from separate resistors (through RF chokes or high impedance lines). So the idle current could be adjusted separate for each transistor. Your situation is relative low power, so should be no difference using the same resistor to bias both (...)
hi everybody. my project use the push pull amplifier, working in 1-30MHz. I using ADS and had some fet model, but i can't know how to build transformer ferrite core model. 1.can you show me how to build it and the manufacturer ferrite core are often used?? 2. a my friend gives me a noname ferrite core,which is bought in china. i use copper wire
What you need is a current amplifier as you micro can only deliver 10 mA and you need 5A (or more). So you need a fet or a darlington power transistor. Make sure to put a diode across the motor to suppress back EMF. I think you need a PI controller ( ). A good test would be to see wha
You meant "Common Source" fet amplifier. Yes, it's convenient to amplify RF signals with a proper fet.
NOBODY makes an amplifier like that except a teacher. Is this homework? The common-gate fet is not needed and the common-emitter transistor has no negative feedback so its output will be extremely distorted.
hi, You could use a higher supply voltage to the amp, select suitable MOSfet's from the 'F2' lib in LTSpice. Adjust the Bias to suit. Post your asc file. E
You'll need some sort of amplifier between the oscillator and the fet gates. Depends on the drive current required. If the fet is small and your layout is good, a bunch of high speed logic gates in parallel can drive fet gate pretty well at 5V. If Ciss is large, you may need a resonant gate drive, in which case you end up (...)
Your circuit is really crude! This is not the good way to obtain a 1 MHz AM modulated signal. You should feed 5 VDC to the crystal oscillator, and use a buffer amplifier in which you can apply the audio modulation. For 1 MHz you can use a common fet amplifier , input to gate and a LC resonant circuit in the drain. Then connect your audio (...)
Why not use the classical diffeential amplifier configuration? The output voltage at one of the drain nodes is Vout=0.5*(v1-v2)*gm*Rd with gm=transconductance and Rd=drain resistance. 1.) It should be possible to make gm*Rd=1 2.) For addition: If necessary one of the input voltage can be inverted (additional fet) prior to enter the amplifier.
Your initial assumption is wrong. LNA respectively fet input impedance is never purely capacitive. You possibly want to review s-parameters of a real LNA. LNAs are typically used for applications related to their name Low Noise amplifier. If low noise is an objective, impedance matching matters.
Hello, I have found from experiment that most LEDs, including UV and IR, can be used in reverse to detect the range of frequencies they are designed to emit. I would like to make a simple detector using a transistor amplifier to drive a meter. Can I use one of these fet static detectors amplifiers and connect the LED cathode to the Gate (...)
transistor or fet or MOSfet in common-emitter mode between the switch and power MOSFT
Hard to tell, u have to read the data sheet. It might stop the drain from getting a +voltage by using a bipolar or fet transistor. It might make the gate voltage go down so that there is little or no current in the active device. In rare instances, there is an attenuator in front of the gain stages that switches off (but you would notice the dra
better then native speakers built-in amplifier with 10%THD. scheme is not very good in fet driving part, but it works anyway. ) (main part of scheme is taken from "Radio-constructor" magazine [url=obraz
A complete schematic would tell the inductor and fet specification. The fet may be simply not suited for the application. In addition, there's no real load impedance. All output power, unless absorbed by inductor losses, goes to the transistor. So it looks like the circuit is working as designed.
It is best when amplifier have k>1. But it is not always possible. Be aware that additional microstrip between grounding and device makes such amplifier behave almost as perfect oscillator, because S11 probably can obtain negative resistance (S11>1). For example, some 1mm on source of fet makes it oscillate in my case, osscilation power even (...)
You talk about the gate of the output device, so its a fet. These have a capacitive input impedance without a resistive component, so It should be possible to resonate out this capacitive reactance, and depending on the Q of the tuned circuit at the output of the driver stage , you should actually get more voltage on the gate then you do on the pre
From the data sheet ( ) you need at least a +4V input to the gate to switch the fet s drain current on, are you getting this at the gate? - which should have a DC return to the drain (100K ?) frank
Are you suggesting that you expect the gain of a fet to be the same when used as an amplifier or as a multiplier? In the old days we used to have to generate 50W+ at VHF frequencies to get 1 W at UHF with a load of multipliers, its the way of the world. Frank
Trying to figure out a way to clear the current input fet amplifier (tens of pA). Before entering the amplifier have a protective resistor 100k on which the current 10Pa an error occurs 1uV. I watched how the proffesional do it. Output short circuits prior to resistance and null current with injected small current. I found, see picture (...)
The fet amplifier protection diodes might be capable of handling the input current in overload case, check the datasheet. Otherwise you have to look for low leakage diodes.
The gain of the circuit will improve as well as the single stage output impedence of the circuit is boosted by the cascaded fet...
Hello! After calculating inductive stub, i have problem how to attach it in microstrip: fet have two source pins. Assume my inductive stub is L, how i must attach it? 1) attach L short stub to one of source pins, other source pin is directly grounded or 2) attach L to both of source pins. 3) maybe attach L/2 to both source pins?
Hello! What is optimal and safe way to do that? Classical approach - LO output at the drain, match 50Ohms output line to Zl=-Zout near transistor. I am going to take LO from gate resonator, so drain port remains unused. Should i match its -Zout to open-circuit, or make "fake" 50Ohm line with 50Ohm resistor and match it to this thing? For exa
When I open textbooks I normally see BJTs, or fets, in the feedback loop but never an ultra low noise op amp, or other type of very low noise amplifier. I was hoping someone who has designed oscillator circuits can tell me why aren't low noise amplifiers (LNAs) normally used for receiver applications not used in oscillator circuits?
A fet set up as an amplifier with an accompanying attenuator pad will work ok (maybe 15 dB of isolation), although it might add additional noise or intermodulation products. But since a fet and resistor pad will cost < 1$, and an isolator will cost is an experiment worth running for a production job. Of course, you realize that you will
Maybe write a little bit more about the application of the amplifier. Signal frequency, desired gain, bipolar or fet, etc...
If you connect the Gate to the ground-in AC meaning-( for instance an inductor) Vg=0 Vs=IdxRs(positive) so that Vgs=Vg-Vs=0-IdxRs=negative. In order to bias your fet around pinchoff, you should select a Rs resistor which would give 1V with Id current.
It would be a lot of gain for a single stage BJT of fet to produce. What is the required input and output impedance?
The question doesn't make much sense without talking about an input voltage range. fet switches might be necessary to disconnect the input. If the problem is about DC impedance only, a RC parallel circuit can possibly isolate the inputs of a high impedance amplifier.
VCM(in) changes the headroom on the diff pair and its loads. Take either end out of saturation and the fet Ro drops, taking gain with it. CMRR is largely determined by the amplifier gain.
For a 15A DC chopper I want some good fault protection. I already have a high side current shunt and sense amplifier for detecting slow overcurrent, but in the event of a hard short circuit this measure would be too slow (several microseconds) to save the fets from destruction. I was hoping to find a fet driver with desaturation detection, (...)
Check here: , this is a class D 30W BTL amplifier with fet preamp and speaker emulator for portable multifunction guitar Pre-Amp. Bye :-)
IF you are limited to a single transistor with the fewest parts.... Consider power gain as voltage gain and current gain. The mic has a fet current source whereby the voltage gain is determined by the load resistance at the expense of a higher supply voltage. Then use your ONE transistor choice to a Darlington biased at a low voltage so
first things I would check are: 1) is the fet adequately heat sunk? 2) is there a chance the fet is oscillating at low frequency (like 10 MHz) and wiping itself out. Did you do a wideband stability analysis. I see a lot of funky things designed into LDMOS bias networks to kill low frequency oscillations.
I guess goldsmith is referring to one of the complementary source follower subcircuits in post #6 (enhancement MOSfet with bias source) or post #7 (Jfet). They don't need GS resistors, the output can be expected to follow the input with a gain < 1, depending on the RL to gm relation. Of course Cgs shows in the amplifier frequency (...)