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34 Threads found on edaboard.com: Diff Offset
Well the design constraints are the noise, speed, offset and power dissipation. For high speed, you will need minimum length transistors. The noise is mostly dominated by the input differential pair. So you have to do a PNOISE sim and keep increasing the width of input diff pair till you achieve your target. Similar exercise needs to be (...)
Hello, Can anyone explain me whether A is better or B is better in terms of implementing a diff pair? Please find the attached for the figure. 114186 Regards, Ananthesh
Can I reduce the input diff pair size and increase the current source transistor sizes to achieve the same performance? If you can provide a link to some text or refer me to some book that would be great. Reducing the input diff pair size is counter-productive to offset voltage, increasing the current source
Gm has a peak and this is usually a little bit below VT. Which direction you'd go, depends on where you started. Increasing gm helps kill the backend offset contribution, whether it improves matching significantly in the diff pair itself I don't think is the issue. I rarely if ever see mismatch data besides VT-match, and there only for a single
How low current do you want to limit to? Your using a AD622, <100uV offset, so unless you need limit at 1mA, advise to decrease shunt resistor, or use a cheaper diff amp, because it seems a waste there. The current sensor should be moved to the input before the series voltage reg IMO. Can't see how your current limit is going to work with the em
Are you saying that in a differential amplifier the input offset will not be amplified too?
I'm missing a specification of the involved gerber formats. The scaling seems strange, I got ten times the physical size when reading the data to GCPrevue. Also the gerber files have arbitrary offsets, I would prefer the lower left corner aligned to zero. Drill data have been generated without an embedded tool table and have an offset (...)
Generally you can improve CMRR by reducing offset and by increasing of output resistance of diff. pair's tail current. If you have simple mirror for tail current you can enhance it to cascode or ever to regulated cascode.
offset cancellation it's necessary for high-gain amplification, otherwise you may have to increase the size of your input diff. pair to make a ultra-low-offset input. anyway, it finally depends on how large the gain is. If the gain is not so large and you can tolerate some drift of the DC point, you'll be fine. btw, even though you've (...)
definitly matching techniques A only............... No compromise for diff pair of an amplifier even it is related to layout area
When I simulate the comparator offset, what percentage of input diff pair mismatch should be set? And what is the typical value of offset when using TSMC 0.18um technology? Thanks!
can any one help me, how common centroid diff pair layout is done and wt are it's advantages. reference to some papers is appreciated, Thanks in advance.
Testing my 10bit pipelined ADC,(SMIC 0.18 process) when diff input both connect dc commen input voltage(0.9V), the output code is not 511. and the output code in 3 Evaluation Board is different respectively(1# is 485,2# is 540, 3# is 604). It may because offset of opamp ,but should not so large(about 50mV). So ,what else may (...)
Some preliminaries: 1. If the opamp have some mV offset and the diff-stage act as a gm-cell you have a differential switched current. 2. If you crossswitch these differential current in synchronism with the input voltage switch to an output current mirror the offset of the mirror does not get chopped (...)
1- The 1.45V is the output common mode, it's not a dc offset. This voltage is the drop from the supply caused by the Vgs of the diode connected loads. You can adjust this value by adjusting both W and L of the load devices. 2- For the architecture you chose, you can't set Vic to 0V because you need Vt of the diff pair devices+Veff of active dev
Gray p231, it is said both offset voltage and current source are required to represent the effect of mismatch in general so that the model is valid for any source resistance... Why only a offset voltage source is insufficent?Anyone konw this?
to simulate offset of a comparator,i use mos transistor model *_mis which is used for monte carlo analysis in spectre of cadence, but i dont know what the 'correlation index' of the input diff pair should be set, anyone knows? and i also want to know how to get histogram thx for ur answer
See my post and reference links on: The best case for matching is diff. pair and cascode MOSTs working in weak inversion region and mirror MOSTs working in strong inversion region. Be care with rail-to-rail input because offset voltage will change with input common mode voltage.
Layout and Circuit. Use input diff. pair with large area MOSTs operating in weak or moderate inversion region. Use well matched load of diff. pair, proper sizing and strong inversion for current mirror. One of source of systematic offset is difference of drain-source voltages of input diff. pair. U can (...)
Sub-threshold (aka weak inversion) region is normal for diff. pair of OPAMP. In this region u've maximized transconductance efffectiveness Gm/Id. This gives u an advance in terms: gain (Gm*Ro=>(Gm/Id)*Va), GBW (Gm/Cc), Input Refered Noise, Input offset/Matching (offset close to threshold voltage mismatch). At the another side the slewrate (...)
All these have diff meaning for diff situations.. wats ure ref situation, ADC?
Hi there, I am wondering whether anyone can guide me for the following questions. Appreciate your help. 1. The first one is a naive question, I forgot why CMOS diff-pair opamp always has very larger DC offset, comparing with bipolar-diff-pair opamp? 2. Why opamp offset is one critical point when designing BandGap (...)
Can any1 suggest me a good offset cancellation technique for a comparator(with a 3 stage preamplifier followed by a latch). I am currently using Input offset storage technique (IOS), but the offset cap value become very big as it has to be much greater than input diff parasitic cap value. Hence I observe an error because (...)
guys please reply the diff between the deadzone and phase offset and how these can be measured. it will be really appreciable
It doesn't makesense of the GBW=450MHz. It's too large. If your GBW=450MHz then your SR will more than 20 v/us. Since your GBW=450MHz, I think your differentail pair input would be very very big. (Consume large area and power). If your GBW wnat be <=100 MHz, there is a lots of type opamp your can use. (like, tow-satge, folded-cascode, balanc
Hallo Hallo Bipolar is Ok , but how to get rid of base current? Anyways it depends , if u have bicmos technology. Generally Take mos as diff pair and try to dimmension it , so that it has enough gm/B.W/ 1%matching error. Don't forget to concentrate on ur current load(u have to consider 1% matching error). Most imortant thing is
Choosing the larger dimension of diff pair may help in reducing offset values or use offset cancellation techniques. hi tekno1, Why are you referring back bias here? Is it not any finite value of Vsb (source to bulk) but it will be same for the both nmos diff pairs? Also, what is impact ionization? thanks -Bharat
That's simple: The offset of a NMOS pair depend on matching of the main physical parameters. There are 1. Threshold voltage mismatch 2. Mobility mismatch 3. Substrate effect mismatch The common mode voltage dependence of the input related offset of the NMOS diffpair is only related to the mismatch if the substrate effect. The (...)
how does one estimate offset voltage in the design process (i.e., opamp)? As a rule of thumb any technologie has a certain offset intrinsic per um . The offset of a diff input pair is proportional with 1/sqrt(W*L) so ..the first aprox you can do is : biger area means lower offset The layout can (...)
Hi As can be seen from the attached figure, there is an equation for a differential pair: Vos*CMRR=Itail/Gtail Could you explain how this is derived? Thanks in advance! regards, jordan76
If you designed your fuly-diff amplifier in the right way, your common mode output level is fixed, whatever is the differential input voltage. So, leave you amplifier in open loop and just scan the differential input voltage. The input offset is the voltage at which the differential output becomes zero. (...)
One other thing also comes to mind. Usually and especially for reducing offset you need to increase W/L, not just WL. For a fixed current, increasing W/L beyond a certain limit will put your diff-pair transistors in subthreshold region of operation, usually not a good thing to do.
There are two view points for the gm of matched transistors and how it affects offset and current matching. gm increases as you reduce Vgs-Vt i.e the overdrive voltage. If you have an offset in a diff amplifier, you'd want to apply a compensating differential voltage at the input in order do remove the (...)
which is the best one? Any idea of the Pros and Cons of differential line speaker audio amplifier? what if if we short the negative line to ground and drive only positive line with single ended amplifier? RG Synq