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52 Threads found on edaboard.com: Opamp Biasing
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 trying to hook up a pressure sensor 79700 to a National Instruments DAQ analog input to read the pressure reading. However as the sensor is unamplified it is too noisy to read. I built an instrumentation amplifier to amplify the circuit with some LM358N that I had lying around. I followed the example circuit in the
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.
Hope these help you............. Op-Amp Basics Part III (Internal Circuit) - YouTube Op-Amp Internal Circuit pages 45......
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
Hi, I was searching the net for this topic but it's hard to find... I have a sine signal obtained by an active opamp filter from a square wave. This opamp has single supply, and so the reference for input and output signals is Vcc/2. But if I have to add a second amplifier stage (another opamp), how can I connect it to the output (...)
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
HI GUYS I AM DESIGNING FOLDED CASCODE opamp FOR SWITCHED CAPACITOR APPLICATIONS I AM FACING FOLLOWING PROBLEMS 1) biasing THE PMOS M18 AND M10 WHAT SHOULD BE THE CIRCUTARY FOR biasing IT OR WAT I HAV DON IS CORRECT THE CASE FOR NMOS M23 ,M24 TOO ( CHECK ATTACHMENT FOR PIC OF DESIGN ) 2) NO PMOS OF CASCODE BRAN
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
How does the bandwidth of opamp depend on biasing current ?
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..
Ok. I've understood ur problem. U try to design bandgap like or Ur main mistake is that u simulate only error amplifier without actual feedback influence. U really need to simulate the whole circuit of bandgap to obtain true dc ope
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.
Hi This is what appears to me: 1. ed_vbias: May consist of a constant gm to generate current for biasing and also generate biases for the opamp architecture ed_OPA_REF 2.ed_OPA_REF: Hopefully a singlended folded cascode as it requires 3 bias voltages. ed_OPA_REF along with M13 and C0 and R0 looks more like a internally compensated linear regulato
Importantly, is the Y-axis right? I mean you have a Y axis which calls of degrees. I do not think so. I do not think that there is an opamp which will cause a 5 degree phase shift. Secondly, have you put the options as .OPTIONS UNWRAP for the phase plot? If you have done so, then the cause is due to two RHP zeroes and not multiple poles. The pr
How can i read a pulsed voltage(PWM) which can be positive or negative, by pic's adc? What kind of circiut must i use before inputting to the adc? Filter, opamp circuit for biasing etc? Also what must i do to calculate the rms value of the voltage? Should i read mean values at certain times over a period and then calculate? How's this job done co
An ideal symmetric opamp surpress the common mode noise components from the bias. If the opamp is used in circuits which have to reject some big signals the common mode noises get modulated by the big signal and distort the wanted small signal. So in addition to AC small signal noise optimisation run a period noise analysis with a blocking signal.
u can refer to a book Analog Integrated Circuit Design by Daved Johns & Ken Martin. In chapter 5 & 6 have depth explaination on biasing circuit for opamp. one of the circuit i have posted at
Suppose in your second stage you have NMOS common-source amp and PMOS current source load. Then your second stage biasing current is mainly controlled by the PMOS current source, and actually Vgs of the NMOS is determined by this current. However if the opamp is used as a feedback amplifier, the common-mode feedback will automatically adjust the Vg