Ok, I got it. The timing resolution is affected by the signal-to-noise ratio over the rise-time of your signal. You find the full formula herer:
Your sine wave input signal has a slow rise time, and therefore limits the time resolution. I reproduced your measurement with a 20 MHz sine wave and got the same result:
If I increase the frequency to 100 MHz and increase the amplitude, I get a better resolution:
This is 5 ps which is better than 37 ps, but still not 2.5 ps. This can only be reached by sending single pulses to the evaluation board which have a rise time of > 300 mV / ns, which can be seen here:
It is important to understand the relation timing - resolution vs. rise time / noise as explained in the quoted paper. If you have tiny pulses from your detector, you never will be able to measure excellent timing. This is physics, and not related to the specific electronics you are using.
thanks for the paper. That makes sense. I thought about sth. like that but wasn`t sure. Couldn´t check higher frequencies (limit of my function generator).
What do think about the other picture I attached yesterday where Chn1 shows a totally different offset than Chn2-4. Moreover Chn4 shows some streaks (red circle) ?
Concerning the offset, it looks to me like you moved the offset slider slider of channel 1 to a non-zero position. You see that from the marker at the very left side of the screen, where the yellow marker is at a different position as the others. Hint: a right-click on that slider sets it to zero. The little streak could be some kind of external noise.
Thank you very much! I will check it tomorrow!
Hello Mr. Stefan Ritt
For DRS4 differential inputs ranges form 500mV to 1100mV, with ROFS set to 1.55V, O_OFS set to 1.3V, the outputs of DRS4 is shown in the attachment.
The left part of the waveform,DRS4 works in transparent mode, and then the readout take place. The DMV of transparent mode is bigger then the readout mode, and that makes ADC sampling harder.How may I solve this problem?
The ROFS signal has no effect in the transparent mode, so you have to adjust O_OFS between sampling and transparent mode accordingly. Either use a DAC or two voltages with an analog switch.
Here's the problem. My external ADC has 2Vpp differtial input voltage range. And the common-mode voltage of the inputs need to be 1.3V. I cannot make both the transparent-output and the readout-output meet the ADC input requirement.
I see your point. Actually I will soon have the same issue since we design right now a board with an AD9637 using the transparent mode. Which one are you using? The common mode range given in the datasheet is limited to guarantee optimal performance. But some ADCs allow a slightly bigger common mode range with reduced performance, but which might still be ok for some application. A "real" solution would be to put switchable level shifters between the DRS and the ADC, but that requires 8 additional chips which is bad. Alternative the ADC could pick up the signal not at the DRS output but at the DRS input, but that would aslo require additional chips for multiplexing. So unfortunately no perfect solution for that...
I'm using an AD9252, 0.9V common mode voltage is suggested and I already use 8 un-switchable level shifters. Just as you said, this common mode range is recommended for optimum performance and the device can function over a wider range with reasonable performance. So I think I could adjust O_OFS to a minor level during transparent output.
There might be a solution. How do you bias th input of the DRS4 chip? If you use a scheme as described in elog:84, you can bias DRS_IN+ and DRS_IN- as desired. Take for example a board input range of 0-1V. For a 0V input, you bias DRS_IN+ and DRS_IN- both with 0.9V. A 1V input signal then puts DRS_IN+ to 1.4V and DRS_IN-to 0.4 V. In the transparent mode, DRS_OUT+ = DRS_IN+ and DRS_OUT- = O-OFS - DRS_OUT+. So if you put O-OFS to 0.9V, you get for a 0V board input signal DRS_OUT- = 2*0.9V - DRS_OUT+ = 0.9V. So DRS_OUT+ = DRS_OUT- = 0.9 V which is in the middle of your ADC range.
If you do now a DRS readout, you need a ROFS of roughly 0.9V. For a 0V input, the storage capacitors have a zero differential voltage (DRS_IN+ = DRS_IN- = 0.8V), so DRS_OUT+ = (0.8V - 0.8V) + ROFS = 0.9V, and since you have O-OFS=0.9V, you will also get DRS_OUT- = 2*0.9V - DRS_OUT+ = 0.9V. So you ranges for transparent mode nad DRS readout mode will be roughly the same.
Yes. I use exactly the same scheme as you mentioned. I'll try your solution.
If using a ROFS of 0.9V, the input would not between 1.05V~2.05V better non-linearity area. Is that appropriate?
To get the good linearity, you need indeed ROFS = 1.05V. With a O-OFS of 0.9V, a zero input signal would give you DRS_OUT+=1.05V and DRS_OUT-=0.75V. I think this is till in the range of your ADC, right? So it's a tradeoff between linearity and available range. I do not know how nonlinear the DRS4 will be for ROFS < 1.05V, you have to try. If it's getting too bad, you still can correct for this off-line.
I have two BaF2 detectors with PMT connected to Ch1 and Ch2. At this time Im using external triger module to start DRS4. My evalution board is version 3 so I have no possibility to trigger on two or more pulses occurence on different channels. But I have this idea, trigger with analog trigger on channel 1 (start detector) will start measurement on all channels. After that using FPGA inside EVM to look if some value in Ch2 is bigger as treshold value for example 0,5V and if yes then send data by USB to PC, if signal in Ch2 is lower then restart measurement and wait on triger in Ch1. This way I want to eliminate false data transfer throw USB. Is this possible to implement it into DRS4 evaluation board firmware ?
It is muuuuch easier to upgrade to a V4 board!
Modification of firmware is not so easy. You have to learn and understand VHDL. Then, you have to add additional registers for this thresholds, which requires modification of the C library as well. The data inside the evaluation boards is not yet calibrated (this is only done on the C library), so you have an uncertainty of 30-40mV in this data.
Ok, except this, I would have a question regarding to the new trigering posibility in V4 board. At this time, I am using Ztec ZT4612 which has some pattern triger posibility. Output from this card is used as an external trigger. Regarding this I have found a problem. Pulses from PMT have about 5-8 ns width. But I need to measure time diferences between pulses in range from 0-50ns. Problem is, that coincidence between pulses is working only on short pulse area (5-8ns) when they are overlapped. Additionaly the result histogram of time diferences is proportional to the pulse shapes. I solve this problem enabling 20MHz LPF filter in ZT4612, so the pulses are wider and overlaped on larger area. But, how it is with the V4 board? Will it trigger if I have for example one 5ns pulse on begiinning of CH1 and second pulse for example 50 ns later on Ch2 with the same probability when pulses are in the same time position?
Hello. I need to digitize pulses from two PMT. After pulse on first PMT I have to save all pulses from second PMT in range 200 ns (and starting pulse from the first, and time range between pulse from 1st PMT and pulses from 2nd PMT). Is it possible with DRS evaluation board?
If you run at 2 GSPS, you have a time window of 500 ns like on an oscilloscope. If you trigger on 1st PMT, you will get the traces of all 4 inputs for the next 500 ns. So I guess this is what you want.
Ok. And, If I understand correctly, the main bottleneck in data readout is USB. I.e., theoretically maximum readout rate is 500 Hz. Is it true?