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58 Threads found on Opamp Biasing
I have implemented an Instrumentation Amp circuit as shown in the picture below: 136589 The inputs ?SIG_POS? and ?SIG_NEG? are coming from a remote location (not on-board) Problems: Case1: When both inputs ?SIG_POS? and ?SIG_NEG? are floating, the actual voltage levels measured at in
For the benefit of other readers: This problem is as old as audio amplifiers. An active stage, whether a vacuum tube, BJT, JFET, MOSFET or an opamp requires some amount of DC voltage "bias" to operate in class "A"; thus allowing an AC waveform to be amplified. Unfortunately this DC would have a detrimental effect on the previous stage, and thus i
The results with the single supply voltage depend on the output impedance of the power supply. The circuit you show feeds half of any hum and noise on the positive supply to the reference input of the opamp. Do it liked this:
Hello, I have collected a direct conversion receiver on 3 breadboards: the first one contains rf stage, the second one contains opamp audio preamplifier/bandpass filter and the third LM386 audio amp in minimal configuration with gain 20. The rf part is based on NE612 famous mixer. The receiver works quite weel (I can hear 10 nanowatt beeping
Greetings to everyone. I am currently designing a folded cascode amplifier, but my concern is if it would be suitable for ultra low power application? like more or less, 50uW without sacrificing it's speed? Here is my reference for this design. I like this paper since the hand calculations are provided but it's not complete. www
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.
Hi guys I need to bias a telescopic opamp with input and output CM at 0.9V. Currently I am not able to bring the transistors in saturation by using voltage sources for biasing. What kind of current mirror circuit can I use? Please help. Thanks!
Hi, Can you guys please help me with designing the bias circuit for the fully diff folded cascode opamp (attached) i.e., to generate the bias voltages Vb1, Vb2, Vb3. 108205 I tried to search in many books, but none seem to explain properly the biasing schemes that can be used. Any reference to relat
Hi, I have designed a folded cascode two stage opamp on 130nm process. The opamp works fine. Figure below shows the gain and phase response of opamp. It has 45 degree phase margin. Now the next step is to design circuit which generated the bias voltages for opamp. For initial case i used a resistive voltage divider to (...)
An opamp that is biased at +2.5V with 2 resistors can be used with an input coupling capacitor to replace the LM386 power amplifier. The LM386 has internal biasing and has internal feedback resistors for a voltage gain of 20. Two feedback resistors added to an opamp can make its voltage gain 20. The output of an LM386 with a 5V supply and (...)
Hi, I designed a folded cascode opamp with gain boosting and it works properly, now I want to design biasing voltages of the opamp. I could design a biasing circuitry for the main opamp, but I had a hard time finding a way to generate the dc voltages that need to be applied to the gain booster input. I (...)
Hi Guys!! I am new to Analog IC design. Could some one please help me with derivation of biasing circuits for a complementary differential pair input for a rail to rail operational amplifier. (Please see the attached .jpg for reference ) Thanks! Saoni
R4 provides a DC path.The small bias current of the opamp will charge the cap otherwise.
I am not sure what is going on here though I my guess is that the opamp output does not have enough voltage to swing about. Could some one help me out here? Thanks You must use split supply, unless you provide a specific biasing circuitry for single supply operation.
I have designed a white noise generator. the o/p is very low, so i used amplifiers to take the level upto mV. I also need to incorporate a dc level to the o/p. I used many circuits for this prupose, but no dc shifting. I tried simple voltage divider, opamp ( Non-inverting ac coupled) biasing etc etc, result is same : no biasing. Here is (...)
The resistive feedback should not disturb the biasing of a properly designed opamp. The problem probably lies elsewhere. At 40dB, you are looking at a 100x gain. Are you sure your output is not saturated? Or is your output so large that the biasing of the output stage is off? Some schematics might help.
The very old 741 (43 years old) opamp usually has a positive supply and a negative supply. Then when its input is at 0V it has plenty of bias voltage. The input can swing positive or negative a little.
hola! what is better solution to feed current mirror through 1uA current path or through voltage one ? the second question is about opamp's biasing. do you bias it locally by simple mirror and diode or do you supply current mirror with reference curent ? regards
it doesn't work... the first opamp is an active filter, to make some filtering on the received signal from the antenna. This stage works fine. ............... I am a bit surprised - the 1st stage works fine? Are you sure? How do you know? To me, it seems to be impossible because of incorrect dc bias.
Why do we insert a large cap on the input and a large inductor in the feedback when performing an AC analysis on an opamp? Like this...
Hi guys, How should I simulate the gm of the input rail-to-rail stage(since gm is dependent with the biasing of the opamp)? Thanks Regards
In typical two-stage opamp, second stage is usually a common source gain stage with current mirror load, like in miller opamp. How to actually bias this stage? Since it is essentially an inverter, the dc operating point of output node is very unstable and either nmos or pmos could easily goes into linear region and kill the gain... any suggestio
Hi all, I'm simulating intrinsic gain of a mos fet using ckt suggested in berkeley ee240 course. (ckt in the attachment) But I don't understand why using opamp here (vcvs in spice) could set the bias voltage correct..Similar bias ckt is used in another cs amplifier example (also attached). Please help~
Hi Guys, I am trying to design a symmetrical load ring oscillator using the self biasing circuit shown in the maneatis paper. Attached is a schematic showing the self bias circuit. My question is, it shows an opamp. How do I design this? Do I have to design each individual stage of the opamp (buffer + push pull, etc.)? Can I substiute (...)
Hi, I'm using Calibre PEX and Cadence Spectre to do post-layout simulation of an opamp. I'm using Charterd 0.35um technology. The pre-layout simulation is alright and i also passed LVS. But the Post-layout simulation is not correct, the biasing point of these transistors looks weird. Take a current mirror for example: MP10 and MP0 f
Hi all and good day! I have question regarding correct biasing of opamp input pins. I am studying desing of fully differential opamp and have misunderstanding of correct biasing procedure. As I understand from books opamp is self powered and biased element so it not need biasing at normal (...)
Does anyone know what this circuit do? The input is from a heart rate infrared/phototransistor sensor. The output goes into an opamp. To me it seems like the voltage divider is biasing the opamp and the capacitor is to block DC. But it also looks like its a highpass filter since the ouput to the opamp is taken after the (...)
Hi; I have a question in biasing an opamp. I only have +3volts supply on my circuit. The opamp i am using requires +3volts and -3volts. So, do i need to generate -3volts supply for biasing? If i use 0volts instead of -3volts then my simulation is incorrect. What is the bestway to fix this problem. Is there a fix (...)
biasing circuit is used widely in analog circuit design to bias circuit in proper operating point. let sat if you design opamp, all the transistors must be biased in saturation mode because in this mode we can get large gain. example of bias circuit is voltage reference circuit, current mirror/sink/source. it depend on your applications. hope my ex
To do this you need to put feedback caps from both outputs into both inputs (in negative feedback obviously). The problem with this approach is that you don't have a direct way of biasing neither the input nor the outputs of your opamp so you'll need CMFB to set the bias. Hope this helps, diemilio
looks like a simple biasing circuit were Vbn and Vcn can be used to bias the N network of lets say for example an opamp, and Vbp and Vcp are used to bias the P network of the same opamp. All the transistors at the far left seem to be part of the start-up circuit. Hope this helps, diemilio
An opamp's input must be biased at half of its total power supply voltage for the highest symmetrical output swing. biasing an opamp has nothing to do with its voltage gain. Its voltage gain is the ratio of its negative feedback resistor to the other resistor (the input resistor if the opamp circuit is inverting or the (...)
hi all i'm trying to design a biasing circuit for an low power opamp. Circuit diagram is attached below. i'm trying to bias the transistor in subthreshold region to reduce the power. but i dont know the proper approach to design the biasing circuit. plz help me if somebody knows the thing... Thnking u.
I am looking for a circuit that can generate the bias voltage for the opamp that I have far that circuits I have looked at are either supply or temperature there any circuit out there that does not use diode and can generate the bias voltage for opamp?
hi all! to bias the tail current of the opamp, bias with which one as below is better 1. Ptat current 2. Constant current
If you place the opamp in a closed loop, as is almost always the case, it depends on the feedback. The gain-bandwidth product (=UGB) is constant in a voltage amplifier, so the lower the gain of the feedback path (return ratio) the higher the closed loop dominant pole in general. In the limit of unity feedback (unity gain buffer) the closed loop cu
Has anyone wrked on the following architecture ? Cud u please tell the design approach for this..And also how to take care of THD in this design..
When simulating opamp, I found that when applying a constant voltage to NBIAS, the gain of the opamp is nearly 50dB, but when self biasing the gain of the opamp boosted to nearly 90db. Who can explain this problem detailed for me,
Could be your opamp is limited by the input common mode range. Try to increase the slew rate of your opamp, that is by increasing the biasing current, which will help in fasten the rise and fall times.
Try to increase the dc biasing current of your second stage design, this will help you to drive the load that slowing your opamp design.
Hi Your question has been defined very generally! If you want to find out biasing in analog integrated circuits (e.g. in Op amp) fundamentally, you may use famous books such as John & Martin, Gray & Hurst, Razavi, their chapters about opamp design; in the first case chapter 6 is the best! but if you want to study for state of the art; I suggest
Hai Guys: I had designed an error amplifier for dc biasing purpose. The stability of the design shown in plot (Stb1.jpg) and plot(Stb2.jpg), are in the range of 60-90 degrees in terms of the phase margin. But I had also been informed that the zero and the second pole shouldn't be located nearby each other to avoid roll off. I would appreciate
anybady know the function of a capacitance putting in the input satge of a AmOpa? thanks
What are the extra circuitry if there is any that are needed in a differential ring oscillator? I saw some use opamp ans something called replica feedback biasing. what is that?
Normally, the bias circuits must make all the transistors of opamp to work in the saturation region
Why would we want to have the tail current to bias an opamp to be PTAT?? The gain of a diffamp is gm ro , and gm = Id/(Vgs-Vth) (Id is the tail current) Vth has a negative temp coefficient so for gm it makes sense to have Id as PTAT to prevent gm from falling. But ro = 2/λId, that would decrease when we increase Id. Is t
hello i'm trying to design a low voltage buffer. i use the circuit as attached. low voltage operation is great. i mean for vdd=1.3V it works very good. rail to rail input ensures wide input swing. the opamp works in a unity buffer configuration. with 10uA biasing it has enough driving capabilities for me. the problem is it doesn't want to
Hi Guys, Currently im designing an opamp for my design familiriaty. If you noticed from my schematic there are 2 PMOS biasing. For bias1, i believe what i have done is correct that is I biasing them according to W/L ratio. But as for bias2, i believe that biasing shouldn't be like that as the VGS is not same at the two (...)
I designed a folded-cascode opamp, and ran the simulation in tt_corner. One of the MOS Ids=13uA, but when used ff_corner(other parameters not changed,only replace tt_corner by ff_corner), then Ids changed to 29uA, so large! And when using ss_corner, this MOS cutoff! How should I do? Thanks.