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95 Threads found on Bias Fet
If "lvt" is just PWell without the main VTN implant, then follow the regular fet rules for PWell inside DNW. You should contact the DNW and bias it appropriately (VDD or some other stiff potential that keeps it reverse biased to Psub / Pwell). Where to return DNW depends on what you want from it. Low noise might argue against a (...)
Yes, you are right, they should be compared with the same Vov voltage. I just use the same Vgs to bias the high Vth and low Vth transistor, and then observe the thermal noise in the current mirror configuration from them. The thermal noise equation is: in^2=KT*(gm)/3. For the low Vth device has higher Vov, with the same Vgs bias condition, which
I used BFP420 at 5GHz in Negative Resistance configuration, which works better than feedback configurations (at least in this case). Have to spend some time choosing the right bias point and tuning the resonator for the right frequency range.
An opamp has two inputs. It has the non-inverting input (+) that needs a bias reference voltage (sometimes not a current) and it has the inverting input (-) that has the negative feedback resistor.
A BJT has a fairly low input resistance that needs a bias current. A Jfet and a Mosfet have very high input resistance that need a bias voltage. BJTs are small and large and can operate at low or high currents. Most Jfets are small and operate at low currents. Many Mosfets are large and can (...)
yes, indeed, or indeed the TLV431 which has a lower ref voltage and less bias current draw. However, the bias current can be a problem as if the cct isn't done right then youll end up with the pfet on when you don't want it on,
But a Jfet is a depletion fet, its gate needs to be below its source voltage so a voltage divider is needed at the source, not at the gate. A single source resistor to ground will bias it and the gate can be at 0VDC. The source resistor can have a parallel bypass capacitor to increase the AC voltage gain.
Hello torbai, Thank you. That helps! I am designing a Power Amplifier. Have lost touch with ADS so trying to figure out things. Also, I used the optimized bias points. I simulated the Sparamteres. The S11 looks horrible. So, i want to proceed with the Small signal matching. How do i find the impedance of the transistor? I wi
Not enough drive current for Q8 to fan. Use a 1V Nch "logic level" fet <<100mOhm. and consider Thermistor on hot spot to regulate bias a fan speed with injected triangle wave to get PWM. V CE(sat) Collector-Emitter Saturation Voltage (I C =500mAdc, I B =50mAdc) Vce(sat) = 0.75Vmax Note : Ic/Ib=10 is common switch configuration, unless special
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 (...)
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
A device's "rating" has many facets, if you drill down into the details. The foundry will call it out at its lowest limiting aspect. It's quite likely that a fet has a higher Vgs and Vgd than its long term reliable Vds at worst case HCI bias. So sometimes (in some topologies) you can safely use a device beyond its simple scare-the-innocent rat
Dear All I have a slight problem in my design, I am trying to design a 25W PA from 10MHz to 512MHz and did some AWR simulation, Steps are given below 1- IV Curve to bias point 2- Stabilize fet 3- Find input impedance and its conjugate 4- Do Load Pull measurement using AWRDE Load-Pull wizard now after doing all that I got input impedance
1) You might just connect a fet as a MOS diode and bias it with 1uA/square and pick off the voltage, if you can't find a .probe syntax that gives you the operating point value. The model parameter value won't change. 2) mobility drops meanwhile, so you have a foot-race sort of situation. Extrinsic resistances also rise. That's why we use simulat
It seems clear to me you have a depletion mode fet with and IDSS of 30mA at near zero bias voltage on Vgs. What's the problem?
I'm not sure what you mean by 'drained to near ground'. If you mean 'completely non-conducting', if there is no active driving voltage/current to force removal of bias, it is usually done with a resistor across the base/emitter or gate/source to leak away residual charge that might be enough to partially turn the device on. It is very difficult
Voltage drop depends on source voltage, dynamic resistance of fet from bias and load R. YOu define what transfer function you want first.
I don't what "bias" means in this regard. Gate driver supply by isolated DC/DC converters is standard in power electronics, particularly for switcher voltage levels that can't be achieved with bootstrap circuits, or if other requirements demand an isolated driver supply (100 % duty cycle capability, startup conditions, ruggedness). I translate
It's very unlikely that the fet circuit does what you want. At least transistor DC bias and R and C values seems to be far off.
You should do these things properly and respectively to turn off the PA while the Load is still connected. -Switch off the input signal -Turn off the main bias -Turn off the gate/base bias
In ADS there is Design Guide and then Amplifiers then there is BJT/fet IV curves .. you can learn how to define bias point from there .... and also google it
I want to incorporate a 10mA constant current sink into a design as a sort of dummy load to bias a larger current driver. I found the Texas Instruments REF200 but it only sinks 100uA. Then I also found the NXP PSSI2021SAY but it is unclear to me whether I can use this part as a sink despite being intended as a source. Can I simply connect the cu
the fet gate needs a slightly negative bias voltage on the gate to operate correctly. So they use a bias network to inject DC voltage onto the gate, without adding any RF insertion loss to the RF path. The 10 NH and 100 ohm resistor act as an "open circuit" to the RF signal, and the 1000 pf shunt cap keeps any stray RF from leaking back to (...)
Surely with the gate at +2.5V the Jfet should be fully conducting and at ground, it should be off? To turn the P-fet fully off, you have to apply positive Vgs, e.g. +4 or +5 V in your circuit. Applying a negative Vgs (gate at ground) will in fact further increase the drain current, but also forward bias the gate junction, which
Surely the internal linear regulator alone would draw more bias current than that? Surely not. Why should it?
I'm using an mrf1513 as a driver for a larger device. I noticed as I varied the gate bias the output on the drain would vary quite nicely and then suddenly step to a larger value. The step only occurs at high drain rf voltages. The rf on the drain swings to a peak of around 30v and minimum of a few volts negative. If I reverse the change to the gat
If the gate is truly pinched-off when there is no input, then it can not oscillate. So I would guess that it is NOT pinched-off as biased. In any case, you have an unstable circuit, and you need to investigate it to change the input or output matching network to make it unconditionally stable.
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.
Many informations missing, e.g. frequency, fet type, magnitude and waveform of the demodulating signal. It looks like you have much crosstalk of original signal. May be a matter of fet Cds capacitance, missing bulk bias or unsuitable demodulation signal magnitude. I guess the "desired output" has been generated by using ideal switches or (...)
My output characteristic curves only go down to about 50 mA, and I want to bias this fet at about 150uA. I have been able to get a biased circuit using this fet spice model to work in simulation. With this spice model you should be able to plot the (for you) interesting range of the output characteristic,
The reason of the negative bias is to increase the input/output isolation when the LNA is in OFF state. In BJT this helps a little bit, but fet's provides better isolation in reverse bias state.
fets are designed to carry current in only one direction so they must operate from a DC source. The voltage applied between the gate and source controls the amount of current flowing through the transistor. Without the proper DC biases the fet does not perform a useful function.
I've seen applications where people deliberately soft-forward-bias fet (or HEMT) transistors to squeeze a little more channel conductance out of them. There will be a max gate current spec that you have to respect. If you can't find a rating then it would be safest to assume zero, but in practicallity a couple of hundred mV, couple microamps DC is
Hello, I biased an electret mic with 10Kohms and I don't get much modulation on the transmitter it is connected to. The load impedance is 50Kohms. Should I increase the bias resister on the drain of the mic's fet to a 50Kohm resister, or would that be ridiculously high? Would it be better to put a 10Kohm resiter across the loaad, to (...)
biasing resistors used: 30 Ohm on drain and 400 Ohm on source. Supply voltage is 2v, so i guess that I=2v/430Ohm=0.0046=0.5mA Yes, it's a guess - but wrong. But where comes this guess from? Do you know the working principle of a fet?
The bias topology of the last source follower fet is a "Combo, Constant-Current / Self-biasing" technique, which was implemented to establish a flat load line without sacrificing the dynamic range. Perhaps can add a different current source than the one is working now, but would be a challenge to tune the bias point to (...)
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 (...)
I've recently been looking at designing LDMOS RF amplifiers, and one of the issues we have is the effect of drain bias voltage and output power on output capacitance of the fet (Cds). It occurred to me that one could maybe compensate out linearity in Cds by using a combination of reverse biased diodes. I did a bit of searching for similar (...)
By nature, linear transfer functions are only valid for small signal and a defined bias point (Vgs/Vds/Id). To derive a transfer function, you need to specify the bias point. Then you shouldn't have problems to determine the linear MOSfet parameters. You're apparently assuming a voltage source driving the fet, thus Cgs won't (...)
So - are you saying that you generally *do* use a biasing resistor from the non-inverting terminal? I generally don't use bias current compensation resistors with fet OPs or input current compensated bipolar OPs. Because most modern bipolar OPs have input current compensation, I effectively don't use it at all. In case of
Right, and I didn't say the bias supply provides energy when discharging the gate. When charging up the capacitance, you draw C*V^2 from the supply. Half of this is immediately dissipated in the driver, and half is delivered to the gate capacitance. While discharging the gate, the 1/2CV*2 in the capacitor is dissipated in the driver again; none
XLV1 is an Electret Condenser Microphone. R3 is the charge resistor for the built in capacitor on the Gate of the fet (in side the Mic) which will discharge according to the voice intensity and will cause the fet to conduct. R2 is the load resistor for the Q1 collector and the R1 is the base bias resistor for Q1. Hope it helps.
The output impedance will depend on the fet bias point and if class C or E operation is involved (discontinuous fet current) also strongly on the RF level.
I have 2 parts of this problem that I cannot change: Mic being used is a electret mic Amplifier unit is designed to be used with a Dynamic Mic. So right out of the gate I know that will have to build a power supply (because the mic will need some bias power for the fet). But what is catching me out is how to replicate the signal a Dynamic mic
You have used high impedance feedback and twin T notch filtering using low slewrate op amps uA741 . The input bias current in these are high .and compensation current reqts. are larger which loads the filters . Pl go for high slew rate OPA like TL084 which have fet input stages and very high slew rates
For HEMT fet switch, its terminal bias criteria never seems to be clearly stated in any standard text. For example, is it okay to set the desired Vgs for switch ON and OFF, but leaves Vd open (or floating, or no bias)? Most people tend to set the desired Vgs, and then leave both drain and source biased with equal potential (
The easiest way is to use a series fet that drives a capacitor to hold the voltage. You can DC bias the gate so the fet is normally off, and has a short pulse turn on the fet. The short pulse can be either from some sort of one-shot circuit, or could be a ac coupled spike from a squarewave rising edge. If you had a much (...)
Hello, i am designing LNA using fet transistor. But when connnect -Vgg with gate of fet, the voltage changed.the measured Vg is not -V as expected. source of fet connected to ground. Is it normal or something wrong?How to debug real bias? thanks.
You are using resistor R1 1K in series with the mosfet source so when the current starts to flow there is a voltage drop across the resistor that actually doesn't let the mosfet gate have an appropriate bias and the mosfet doesn't turn on. In the datasheet examples for your device i see that the load is not connected in (...)
After adding a DC blocking capacitor Why did you place the capacitor in the bias path? The capacitor(s) must be inserted between the circuit and the RF ports.