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Fet Bias Resistor

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17 Threads found on edaboard.com: Fet Bias Resistor
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.
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.
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 (...)
When fet's or Transistors are used as switches, in the Off or Open State the fet and Transistor should be fully off and has drained off to near ground. What additional components do you need to use to make a fet or Transistor when used as a switch to drain off and get to ground? How do you know when a fet or Transistor (...)
Voltage drop depends on source voltage, dynamic resistance of fet from bias and load R. YOu define what transfer function you want first.
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 (...)
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.
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 (...)
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 (...)
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 (...)
Hi!How can I calculate the thin film resistor's power dissipation.For example, for a fet bias using, 0.5V voltage will drop on the resistor and near 100mA current cross it . Best regards! -cqcq
Using a fet as a voltage variable resistor maybe a simple solution. By changing gate bias you can vary the "resistance" between drain and source. Hope this helps. S. H.
Let's consider an electret microphone with usually an internal fet with resistor equal to 2KOhm. I am going to bias that microphone with an LDO and a capacitor multiplier. Just connected at the capacitor multiplier I am going to insert a resistor of 1KOhm, the microphone (with internal 2KOhm resistor) and (...)
I need to design a 1G ohm resistor on chip to dc bias a trans_C amplifier, I know I should use CMOS fet method, but how to realize it? Thanks advanced!
In GaAs fet bias network, a source resistor is used to set the DC point and bypassed by an cap. Why is it said that this cap may cause oscillation? Another question: Is it necessary to make the fet unconditional stable (such as add a parellel resistor at output) before matching networks design? Is it (...)
First of all, the circuit is not a varaible gain. Put the fet connected as R6. Does the input of your OpAmps have an input bias current?
A hint for PA designers: It is well known the problem to bias a power MESfet or GaAs fet due the need to have a negative gate voltage. Does anybody tried to do the gate bias using a resistor at source instead of a negative power supply? I have been using this approach successfully designing PAs ranging (...)