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102 Threads found on edaboard.com: Ptat And
I'm designing fully differential amplifier to utilize at bandgap reference circuit. and I studied CMFB for fixing output common mode level of amplifier. But I have heard CMFB also drives input voltages of amplifier which is virtual short. It is true? Actually I already made fully differential amplifier. But if i connect amplifier with (...)
I'm using Vdd=1.9V for 0.18u technology and obtaining the ptat and CTAT currents. Now i've to obtain the current reference output using these currents. How is it possible to do so?122105
Please refer to the attached circuit. 117083 It's obvious that MP1-3, R1&R2, Q1&Q2 work as a bandgap reference circuit itself. With appropriate combination of the ptat current and the CTAT Veb voltage drop, a desire bandgap voltage reference can be produced. However, what about the middle part? It seems like there's a
ptat is good when you want constant bandwidth against a capacitance that rises with temperature, or constant gain against a device whose gain may fall w/ temp (like MOSFETs). You should work backward from the outcome you want and the device vs-temp behaviors that would degrade it, to the bias profile you want. You may want more than one in (...)
Hi All, I am using the circuit from this paper in designing a ptat circuit "A Novel Wide-Temperature-Range, 3.9 ppm/C CMOS Bandgap Reference Circuit",by changing the input transistor of opamp from MOSFET to BJT. This is the ptat circuit and the detailed schematic of Opamp. Startup circuit is not included in this figure. (...)
Hi , If any body can explain the working principle of this bgr ckt which is attached. or a general bgr ckt. I am confused whether at the input of the opamp, one input should be ptat and other be at CTAT? Ikept the both inputs varying on the same direction with bell shape when we see volt vs Temp. because we have to sum together thats why if sam
1) I had designed ring oscillator with 3-stage differential amplifier with resister load. when bias current for differential stage in constant, I observed frequency is changing with temperature. But with ptat current frequency is constant with tempearture. I didn't undersatnd what was the reason. Can some body help me to understand why ptat (...)
I suspect the best play is to put large shunt C between op amp output and the PMOS-pair gate node in the ptat section. This will help HF PSRR as well. Miller comp in the op amp that keeps its output stable wrt Gnd, will make the PMOS pair amplify supply noise. Of course simple shunt comp tends to want more area than Miller comp, and this (...)
Usually, please some one correct me if I am wrong, there are two stable states for this kind of circuits. Depending on the initial conditions the circuit could go to a state where the current is zero, so for this reason some sort of start up circuitry is needed. There can be a third stable state, if you close the
dear all I have designed a biasing reference current by adding ptat and CTAT currents together. the result is a biasing current with small temperature coefficient. However, since both the PTA and CTAT has R in their equations, the total current still depending on the process variation. not like the bandgap reference (...)
You could start with just what "didn't work" means. A result you didn't like, or failure to produce a result at all? bandgap / ptat loops without explicit startup mechanisms, can easily converge in one testbench and fail in another, because when they start up they're doing so on "numerical noise" which depends on the circuit matrix (...)
Hi Meliza, Well adjusting the amplitude of ur bandgap reference depends on the type of ur reference. If it is in a type that it first sums ptat and CTAT current and then conducting this current through a resistor to generate voltage with low TC, in this way u have to change just the resistor to adjust ur final (...)
I'd use that one with the lowest TC resp. VC -- probably polyres. If you have resistors with pos. and neg. TCs available, you could add them appropriately to achieve a very low TC -- or even (nearly) compensate the ptat TC -- if this is wanted.
The Is term has a non-trivial temperature dependence which explains your contradiction. You can write Vbe=kT/q*ln(Ic/Is) and say that Vbe is ptat. WRONG!
1st order is the ptat, diode TC vs diode+resistor TC. Linear. 2nd order would be curvature-correction. You should be able to find a lot about curvature correction in older textbooks, as much of it had to do with base current / Rb error. Because curvature correction uses a square-law phenomenon of some sort (whatever you can find) it's tricky a
hi all, i got PATA current from Razavi at chapter there is no more detailed start-up for this circuit. whether the circuit needn't start-up circuit? if start-up circuit must have, can anyone recommend or what document i can r
I just read the paper "Process and Temperature Compensation in a 7-MHz CMOS Clock Oscillator" by Krishnakumar Sundaresan. There is a cicuit as attached which is temperature independent current source. But it looks like a ptat current source in some kind of bandgap structure.Can somebody explain "temperature independent current source" to me? (...)
The attachment is a CTAT and ptat current generator circuit for low voltage operation. My understanding is that as temperature increases, the Vbe(Q1) decreases and Id5 decreases since Vbe / R2 has decreases. This generates the CTAT current. Combination of the CTAT and ptat currents makes a (...)
Hi palmeiras, here are some new outcomes from my side: 1) When you wrote: “the resistor leading to a reduction in VGS2=VGS1”. Do you mean VGS2 minus VGS1, right? Because VGS1 is always different from VGS2, never equal. Sorry, this was a typo: Of course it must be Vgs1=Vgs2+Ids2*Rs=Vgo2 (referred to ground). A last thing:
Compensate a ptat current with a CTAT current.
How to simulate a ptat circuit? Run a DC analysis and sweep the temperature. can someone show me how to set the parameter of the component for ptat circuit? Your question isn't clear to me: Which parameter of which component? How is your circuit? Schematic, Verilog-A, AHDL, functi
In bandgap, the ptat current is obtained by the delta_Vbe/R circuit. The implicit assumption is that the same current flows through both transistors! In Bandgap A, the opamp offset and mismatch will contribute to the current difference. In Bandgap B, if we ignore R2/R3 for the time being, the current (...)
The bandgap voltage of silicon is 1.12eV. That is Ec-Ev That does not depend on a mosfet channel length. Maybe you mean the "magic" voltage that is typically the output of a Brokaw bandgap cell? A current summing bandgap can add ptat and CTAT currents below 1.2V rather than adding (...)
You'd have to show the circuit, but I have personally seen ptat loops in bipolar technologies exhibit three stable states - "off", "setpoint" and "saturated" (current mirrors of some forms have a superlinear response (out/in) when their devices saturate, while others are sublinear and do not have such issues).
I need bias voltage which changes with temperature, so a ptat circuit. at -40 C , the voltage will be 900mV and at 125 C voltage will be 960mV. that means, change is 0.36mV/C. I designed a circuit but its changin from 500mV to 1V for -40 to 125C. Can I designed such ptat which is change 0.36mV/C ?
Hi Yitch, First you need to understand the concept of ptat and CTAT in bandgap reference. if you dont understand the complete circuit of bandgap then just break it into several pieces. like opamp, current mirror, diode or bjt combination, role of two resistor if you are (...)
Could anyone explain where's the positive and negative feedback in the attached ptat current ref? Thanks a bunch!
A ptat current reference circuit is based on the concept of adding (subtracting) vbe voltages. Typically you would use two vbe voltages with different areas and a resistor closing the loop to put the ptat voltage across it. Such a circuit has two stable Operating Points, one of them is with every voltage equal to zero, the other one is the (...)
... 1. To generate a bias current why is a ptat current generator used. The current will be proportional to absolute temperature so won't that affect the circuit performance. Instead shouldn't a bandgap reference voltage be generated and then use that voltage to generate the bias current? ... 3. ... Again I don't understa
Can't make a ptat without a resistor. A trimmed resistor is process invariant, in the end. But you pay a cost in area and test time to get there.
as we know, there is a opa in the ptat circuit.and the opa has a positive input and a negative input, we should form negative feedback to make the two input terminal have the same voltage.Usually, one of the two inputs of the opa is connected to the triode branch,and the other one is connected to the branch which conclude a (...)
Dear all, Currently, I am doing a ptat circuit design using traditional pn junction. I found the linearity of output current will be different when I choose different material of resistor. experimentally, rpoly2 has a positive Temperature coefficient, rpolyh has a negative TC. I am thinking of mixing these two type of resistor to cancel the impa
Hi For 1.5V supply I would not use the classical bandgap approach The classical approach will show some serious problems in the low-temp/slow corners, especially during startup ... Look out for some papers about low voltage bandgaps. The basic idea there is, that you add a ptat and an iptat current. (...)
If you have current mirror racks in your ptat / bandgap, then adding yet another mirror with a different combination of emitter area and emitter resistor can produce yet another temperature coefficient (more resistor makes current TC less positive / more negative). A MOS mirror rack might not be quite as well behaved, don't know how (...)
I'm not sure that your process has the luxury of NPN but not the substrate PNPs. Coming to the schematic, your reference is referred to the supply instead of ground. If you use the ptat current and generate the reference wrt ground you wont see huge supply dependence.
Marked up; the diff pair and mirror naturally must match; the common-source gain stage has a matching requirement but not 1:1, its load current needs to be 1/2 the diff pair tail current (assuming unit devices) for equal current density / VT. In the ptat reference matching may not be strictly necessary but hygeine never hurts. The output Clas
I have seen this circuit being used to establish a ptat bias current in the right branch of the circuit. The interesting thing is that this current does not depend on the current in the left branch. Usually, and I mean in what I've seen, the left branch just carries a small start-up current. So, if this is what you're asking, yes, the left branch c
The equation you're writing is correct. What you have to take a look into is the following: The circuit shown is supposed to generate a ptat current by having the voltage that you called VR across the resistor R1. The reason this current is proportional to temperature is because the difference of two base-emitter voltages (Vbe1+Vbe2 and Vbe3+Vbe
as we know, an opamp is usually used in ptat circuit, and its DC gain should be large; but what is the DC gain requirement? how to determine the value of DC gain, and how much is enough? can anyone give me an explanation?thanks.
first, if i use a ideal switch (switch of analoglib) to simulate something, and it has 4 terminals N+\N-\NC+\NC- , then how to simulate a ideal swith use it if i want to use a pulse to control its on\off,when vclk=vdd,it is on,when vclk=0,it is off? i use N+ and N- for input and output,NC- is grounded,NC+ connects a pulse(vpulse of (...)
you implement temperature insensitivity by forcing an NTAT current , a ptat current and a ptat-square current, rather than an NTAT+ptat current
i designed a ptat reference in 0.18mm process, but i find the psrr is only 48dB (0~1KHz),and above 1KHz, psrr decreased gradually. is that ok? and how to improve it?pls tell me.
how to analyze the ac and dc characteristics of opamp(cascode or two-stage) and bandgap(ptat)? which aspects do the ac and dc characteristics contain? how to analyze them in general?
pls tell me how to calculate psrr of ptat reference(in theory)? and how to get the psrr expression from the circuit visually? thanks. is there any advice or papers?
dear lhlbluesky: In my design, ptat: to combine bjt to output a reference voltage for common mode voltage. constant-gm: for gm- filter and AGC. mpig
Hi, By equating Vo1 and Vo2 you impress the difference in VBEs (which is a ptat...Proportional to Absolute temperature) across that resistor which forces the currents to be ptat,. which you need to generate a ptat voltage to sum with CTAT voltage inorder to get BGR. Without the resistor, you need to amplify the (...)
by using temperature dependent element like voltage of diode or ptat current. As a starting point I would suggest to check the bandgap voltage reference, I would simply modify a basic bandgap....
Simulate the supply ramping with a transient simulation. Use either a positive and a negative offset on your error amplifier. If only one polarity works you get the issue. Startup in CMOS bandgap set the operating point at a value where the ptat generate enough voltage to overcome offsets.
i have designed a ptat bandgap,which is current mode,that is,vref is generated by only a resistor,and the current is consisted of vbe2/r2+deta(vbe)/r1,so vref=(vbe2/r2+deta(vbe)/r1)*r3;i don't know whether it is clear; my question is, i use csmc 5v high voltage process,and when i simulate the temp coeffient,i find that (...)
a) ptat, NTAT, CTAT? b) only CMOS or bipolars allowed if bips are ok - just tak a simple bangap reference and take current out of it. 5uA would be ok.