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36 Threads found on edaboard.com: Vref Dac
vref is the maximum output that dac shall give when the biggest binary input word (0xFF for 8 bits) is given. vref is the maximum voltage for which an ADC shall give the biggest binary output word (0xFF for 8 bits). I don't know what will happen if the input to the ADC is bigger than vref though. Why do many ADCs have (...)
First eliminate all static sources of error using a calibrated dac. THis includes ground shift of vref from digital currents and thermal drift of vref. When I designed a 12bit SCADA system in the 70's I used BB 12 bit ADC's and dac and was happy with dac but had issues with monotonicity missing codes and (...)
hi all i am working with dac 0808 i have implemented the circuit given in the datasheet (circuit schematics is attached)108209 i have changed the positive vref to +12v and vee to -12v and capacitor bypass to ground on positive vref ,rest circuit is same, the problem is after giving power to the system IC 0808 get heated ,
I use STM32 discovery value line board. Normally, the voltage that get from dac of this board will be 0-3V from the define value 0-4095. But right now, the voltage that I got it vary between 0-300mV only. As I know, this board is the old board and never modify vref. Could you please help, what should be cause of this problem?
Hi there, I have heard that an internal ADC used in the delta sigma (DS) ADC is a low resolution one, but the internal dac needs to be as accurate as the whole DS ADC. Assume we want to design a 10-bit delta sigma with a 3-bit internal flash ADC. we know that offset of flash ADC could be less than vref/2^3. But what about dac, its offset (...)
Hello, I am looking for a differential resistive dac in literature/papers, which - has single vref reference voltage - common-mode of output differential signal is CM -and CM > vref I didn't find any information/example/paper. Could you please show me such examples? Thanks.
Hello, SAR - ADC clock period = 1/20Mhz LSB size = vref / 4096 for a 12 bit ADC So if vref = 2.5V, then LSB is 600uV As a general rule the settling must be within (1/2)LSB in (1/2) clock period Is there any ADC reference buffer architecture that can fulfill such a tight requirement ?? Should I use a voltage regulator which has a fast load regulati
Unless you are following special intentions and fully understood the function of each dac0800 pin, you should refer to a standard schematic from the datasheet. vref+ and vref- are the reference inputs and can't work when connected to the supply rails.
Hello everyone!!! I m using dac in LPC2148 ARM7. Here Pin 9 has been connected to resister divider network. this divided potential is fed to op-amp. now when i write a value in dacR resister o/p on pin 9 is shown acc to the value written with respect to vref. but when i rewrite the value in dacR which is lower then previous (...)
Can any body suggest me dac specifications ,required for SAR 4-bit ADC.How to start the design ? what can be the values for Resister and op-amp specifications like gain etc and vref required ? please suggest some guidelines to design.... Thanks in advance..
I am designing an 8-bit capacitor dac (thermometer coded). I am confused about the clocking in the dac. I have gone through several datasheets and I didn't find the CLK pin on any dac chip!! They just have supply pins, input-pins, output, and vref. Then what about CLK signal? Are the clocks generated internally or how (...)
I need some help in understanding how a dac's programmable gain is used and how to change it. The circuit I am working with is using a AD5446 dac from Analog Devices. The Rfb is set up as the input and the output, Iout1, is fed through an op amp before being feedback into vref. I am pretty lost on where to begin or what to do. Overall, (...)
What ever vref you decide with direclty affect your opamp specs . vref is normaly given and from vref we decide LSB and opamp specs .
look at my answer in your previous thread, you seem to be using the unipolar configuration which has an output of -vref to 0. Alex
when the input will have the same voltage as the vref value the output will be all 1s (this depends on the adc and if it supports negative values). In general for a 10 bit adc you have 1023 different values so each step will be vref/1023 for example if vref=5v then 5/1023=0.0049v so if the input is 0.0049v the output will be 0000000001 (...)
hi all, I want to do adc in pic18f452. For verification i am applying a sine wave(amplitude=1v and frequency=2Hz) as an analog input to the pic and want to convert the digital output of pic again to analog sine wave using a dac0808 pic18f452 has a 10bit adc but i have adjusted the input voltage and vref in such a way that digital output is in 8 b
Hello, i am working on SAR ADC design in cadence schematic composer..i am getting proper ouput from shift register but after shift reg. to SAR register ,not getting proper output...can any one help me? for 5-bit dac , shift register output is 10000 but therotically,we get out of 2.5v for vref=5v..but practically, i get 0.3125mv.. a
Hi, I think you need only a +/-5V supply for the Op= its done! K. Added after 5 minutes: These becouse dac8831 has self an voltage output between 0V & vref! With the OpAmp as a buffer only you have it repeated/amplfied, bat if the OpAmp is connected into your circuit (with dacs onchip resistors); control
there are 256 resistors placed from vref to gnd and some switch behind of each res node,when one of switch is off and another switch is on the charge will be injected in the res string and the node voltage of res string will be changed ,through about 500ns the node voltage back to the initial value , this time is so long and the output voltage will
I am having some difficulty with this circuit. My input is an iPod who's signal centers around 0V and swings +/-1V. The ADC, in this example, is set to 12-bit processing. According to the transfer function and when vref+ - vref- = 3.3V, the theoretical ranges for conversion are: 0V - bottom 1.65V - midpoint 3.3V - max My op amp circuit
hi i want to calculte the INL/DNL of ADC, the method given in "cmos analog circuit deisgn " by allan and holberg. in this method he described that put an ideal dac after ADC and sweep the input signal from 0 to vref and make the differnece of dac output and input signal and plot this equvalant vin-vin1 with respect to input . we can then (...)
could you re-upload a more clear pic? in generally, the r2r calculate is easy, please from the terminal close the vref,then one by one to the termal close the opamp.
hi, i'm reading the book cmos analog circuit design by Allen and i have a question about the charge scaling dac. if the switch S1 is closed, the voltage of C1 is vref and the voltage of C2 is zero, and i think it will not change whether S1 is open or not. So Vout is zero, it's impossible. i don't know what does S1 use for in this circuit. [ur
Hi H_D_R, The equation given by you is same as that given by Mr Murali as shown below: Vo = KRf ( A1/2 +......+ A8/256) ----(a) ; where A1..A8 is a binary number From the above equation, vref = KRf (1) ----(b) ; (A1/2+... +A8/256) =1 since for vref A1 to A8 all are one. Dividing (a) by
Bottom plate should be connected to vref+/-. As bottom plate is always connected to vref+/-, so impedance is low, relatively compared to some floating nodes, so insensitve to noise. Remember all floating nodes are sensitve to noise as impedance is not well defined and any charges from noise injected to that node will accumulate and cannot skip aw
Deal all: Today, I study the R-2R dac, I find that I can not calculate the voltage by hand. I draw a pic show below. If S4 is high, it is easy to calculate that vout is 1/2 vref, but if S3 is high and the other is zero, how can calculate the vout by hand? I calculate it and vout is 1/4. but if S2 is high, how to c
IN PH1 AZ close and dac input vin,in ph2 az open dac input vref then C1 C2 function? please help me
I going to use an dac like the simple schematic below. The Vin on vref is Multiplied/Divided with the digital value inn the dac. I have understood that there are to types of dac; voltage and current. In the datasheet for the current type they are refering to Multiplying dac, while on the voltage type (...)
Can we connect negative vref pin of dac 0808 to -10 voltage.? I tried but it was not ok. vref_pos=+10V,VEE=-15V. Please help !!!!
In the pipelined ADC, there needs vref+ and vref- voltage for the dac. Because of the large number of stages, the caps load is huge for the reference voltage, which requires buffer for the quick settling. I have two questions about it. 1. All stages share only one reference buffer, or each stage use one. The reason is I concern the (...)
Voltage that the dac could convert, 8 bits means 256 "levels"(2^, and the resolution should be: vref/256; in the case of vref= 2.5 Volts, 0.5 would be represented by aproximately 51 in binary "00110011".
hi all, I am a rookie of this board. Does anyone know what is the vref which in the attached Figure? and how many amplitude of vref? thank you Hi, The vref shown in the figure is the voltage associated with the feedback dac. If the output of the comparator is high, +vref/2 is selected and fed back (...)
The resistor to the summing junction should be connected to the vref (2.5Volts), isn't it?. I am thinking in using a non-inverting op.amp.
Max512 is maxim 8 bit dac with ext vref pin, it is not special multiplying dac,can I use it for multiplying dac function?
connect to negative or positive vref means to connect vref to negative or positive integrator input. vref is positive.
Can you be more specific? The M-dac function is: Vout(t) = vref(t)*Din(kT) where T is the inverse of the input digital sampling frequency. I assume you request a wide-bandwidth Mdac for the vref? Willy