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1000 Threads found on edaboard.com: Opamp Output Impedance
I am trying to measure the output impedance of an opamp in the attached configuration. Results are attached. Basically, Zo = Vo/Io = 10mV/40mA = 0.25 Ohms. Without the capacitor in the circuit, I get mostly a large dc current. Is there a better method to measure output impedance? I would like to (...)
opamps DO NOT HAVE a single-ended collector output in class-A. Their output is produced by very low output impedance complementary emitter-followers in class-AB.
hi To get a low output impedence (need when drive resistive load), you can use opamp as a buffer, prefer use rail to rail opamp because r2r output can go to very low voltage. If your output driving capacitive load, high output impedence has no problem to drive, for example gate of (...)
hi, |IAngel| I think aryajur's reply hit your point. You can find simulation of opamp in Allen's book, second edition section 6.6. BTW:you said your supply is 500mV, quit low. What process do you use?
can you give me some papers about simulation of input/output impedance of opamp both open loop and closed loop. thanks To measure output impedance, regardless closed loop or open loop, u just put ideal current source Idc with ac=1 at the output, then measure the voltage at the (...)
Hello all, Would some one help me to figure out the formula of the output impedance of a class-AB opamp? I attached the schematic of the opamp. My purpose is to reduce the output impedance of the opamp to about 5 KOhm (currently, it is 28 KOhm).
Hi all, what we have learnt is that the output impedance of an opamp is very small. I cannot seem the find this information in the datasheet of the opamp I am looking at. May I know how can I measure the output impedance of an opamp using only spice?
what's the output impendence do you preferring? a R-R opamp plus push-pull MOSFET pair is an option. mike -------------------------------------------
How to simulate the output impedance? Thanks!
Thanks supposing your amplifier has a one dominant pole, you can plot the Bode's diagram of the opamp gain and then calculate: Rout=Aol/Gm where Aol is the DC gain you can read from the Bode's plot and Gm is the global transconductance of the opamp (which value also depends on with how many stages the opamp is built
XF is very usefull for CMRR and PSRR characterization. output impedance u are able to easy obtain using AC analysis. Just put AC voltage source (e.g. 1V) with 0V DC in series with output of amplifier. Measure AC voltage at ouput and Ac current flow though output: Zout=Vout/Iout P.S. Generally when you simulate (...)
... It should deliver as much power as possible to a 20 ohm load. Therefore, I am trying to make the output impedance as near to 20 ohm as possible. No, to achieve this, Rout ≪ 20Ω ! Thus, obviously I should use a common drain MOSFET. However, the problem is output impedance of a common drain mos
If you neeed output resistance to be exactly 50Ω, I would recomend you to use an opamp voltage follover and attach a 50Ω resistor to it. With your circuit, you have to know the output resistance before you can alter it by adding a resistor to it. I'm sorry to say I can't calculate the current output (...)
Why is that the output impedance of the OTA is ideally very high? I thought we need a high output current but why is it that the ideal output impedance is very high? Can you please explain it to me? In contrast to the well known opamp (which is a voltage source) the OTA shall act as a (...)
Hi dino, two additional remarks: What do you mean * with "ideal amp"? Transistor, opamp, OTA? * with Rout? (The term Rout in your formula primarily consists of the load resistance and - in most cases - is not the output resistance of the amplifier itself).
A common gate amplifier is very different from an opamp or a common source amplifier.
why the LNA in o.18um,in the different processor TT,SS,FF,the output impedance changed very much the TT Z=35-j*41 in the SS Z=60-j*62;and in the FF,Z=7-j*7 who can tell me why ,my LNA is cascode instructure .
How to measure the output impedance of closed loop system in the simulink? Such as two-loop system controlled by digital controllers.
Hello, Is there anybody who already designed a PA that should drive a SAW filter ? Should we provide a particular output impedance to the SAW to reduce VSWR ? Lots of design papers says that you should transform the load to the optimum load to have best efficiency. Suppose I have a 50Ohm SAW filter that is terminated with a 50 Ohms impedanc
I am designing a LC-VCO,would you give me any advice on the following questions: (1)How to calculate the output impedance of LV-VCO? Because I should do the impedance matching when measurement. (2)I ever saw that the buffer and Bias-T are added into the LC-VCO for measure on IEEE papers.What the role of the buffer and Bias-T?
Hello! How could I get only positive pulses at opamp output? I mean Look at the picture attached. Supply of opamp are: +5V and -0 gnd. At input V+ is sinus 18*sin(2pi*50*t) and at V- is DC 10V. I want positive output of opamp only when positive sinus i greater than 10VDC. Thanks.
for example: op ,buffer,....
The circuit is the simple differential amplifier where the output is taken differentially as Vout1-Vout2 and the input is given differentially Vin1-Vin2. What is the output impedance across the output. Is it ro||Rd or is it 2*ro||RD ?? And why.
I got some question about opamp output stage. 1. Is it necessary to have large current in the output stage? why? 2. Should i add a miller compensation cap between input stage and output stage? just as in two-stage opamp? 3. The main purpose of the output stage is provide low (...)
Hello, I have the output of my audio amplifier with 4 to 8 ohm output impedance which can give 350mW of power to 8 ohm speaker. I want to make it 600 with 350mW of power, how to do it? What is the meaning of 600/600 matching transformer? Waiting for your encouraging reply, Regards Bakhat Rawan
How to calculate the output impedance of amp with feedback when I want to calculate the openloop gain,thank you.
How can I find output impedance in Cadence? ( I mean the whole circuit's o/p impedance and not transistors' ro) I have to use one of the periodic analysis types because my circuit is driven. Is there something quick to do that? Or would I need to add a port at the o/p, and use PSP analysis? Thanks in advance
From the attachment, is it the right way to measure the output impedance of a hardware circuit? Rs is the output impedance of a discret circuit. The Out will connect to V1 and get the Out voltage and after that the Out again connect to V2 and get the Out voltage. And after these 2 measurement, solve the equatioin to get out (...)
Does anyone know why LVPECL interface do not care its output impedance 50 ohm to match 50 ohm transmission line?
Dear all, How do I find output impedance in my current source? I use hspice. Thanks.
Hello there , I am wondering why we are used to shorting the input terminal while finding out the output impedance of any ckt . Based on two port networks Z?? is defined like that ,ok.Then tell me how it yields good results even if we use the same op resistance(for which we shorted ip and found the impedance) while (...)
the balun model in spectre (verilog-a) has an unbalanced input impedance of 50 Ohm and a balanced/differential output impedance of 50 Ohm. these impedance values can be varied. to my knowledge, if the diffrential output impedance is 50 Ohm, each output has an (...)
I have vector network analyzer, which can measure input impedance. I just put device on port 1, and measure the S11, then can get Zin from S11. For there is no output power from the device in port, and the measured power is just the reflect power, which is a portion of port1 output from the analyzer. But some device can out (...)
Hello experts, Do you have any practical experiences on how to measure power supply output impedance? Say, to identify its output impedance <0.01Ohm@DC and 0.05Ohm@1MHz. Any comments or hints are welcome. Best regards, bittware
Why the current consumption varies with output impedance when using collector-voltage control (ex: RFMD3146) power amplifier ? Is it a common phenomenon in PA design ? Thanks.
Regarding PA, different output power level resulted in different output impedance. Is this because of DC bias change so that it changes the characteristics of PA ? Thanks.
Infinite input impedance means that the opamp draws no current, which means that all of the current goes to the load. Zero output impedance means that there is no voltage drop within the opamp, which means that all of your signal is delivered to the load. Hope this helps
in general you want to have high input impedance and low output impedance. this type of circuit is more immune to changes in the load. opamp was designed with this goal in mind.
the efficiency of any amplifier depends on the input and output impedances, so your design goal to achieve a very high input impedance and a very low output impedance , the ideal opamp has infinity input impedance and zero output impedance (...)
When I do not connect any load resistance Rd, what is the output impedance of the cascode BJT in terms of gm,ro,r π (pi)?
Last time i asked about input/output impedance formula with reference to one circuit from a boook. I got good info at my post . But now i found another wideband circuit of similar type from I am herewith posting pages
Is there any easy method or software to find input output impedance of transistor at RF frequencies with help of S parameters?
What is meant by output impedance and what is its importance i know what is meant by input impedance and that it should be large for amplifiers but what is the importance of output impedance in amplifiers should it be large or small
Hi, Would like to know what is the implication(advantage or disadvantage) of having high input impedance or low input impedance in a circuit. What about high/low output impedance? Thanks
Hi, there I know some guy suggested to use statement, what if i just want to see the the change of ro with respect to the change of other quantities, say, output voltage. how could i write my spice commmand.. TIA Julian .
I am trying to make an audio amplifier using the lm741 op amp, and I want to measure its output impedance , so that I can attach a speaker of matching impedance, this way I think, I will be transferring more power,, but how do I measure the output impedance of my circuit, also are there any (...)
Hi, I've got a receiver which mixes down a 1GHz signal to ≈ 100kHz. The receiver has two outputs (differentially, 180° phase shift) which both have an output impedance of 65Ω. In the datasheet of the receiver it says "The loading resistance on each output (single-ended) should be larger than 300Ω to assure (...)
Dear All : I design a LNA now , the band is 70M ~ 120M , I usae spectre do simulation. I Run SP , PSS+ Pnoise. I have some question about the simulation. I use Vport or Vsource fot input / ouput. My question is input is 50 ohm. How to define the ouput impedance ? The Next stage is Mixer. I read some document , it apply ouput impedance is 50 oh
hello i built a small fm transmitter.pls tell me how to measure the output impedance of the oscillator stage inorder to match the antenna.
hi i need to measure output impedance of a circuit as a function of frquency, in spectre.... can anybody tell me just how to do it.... or can i get some good user guide of spectre... thanx in advance...