On Wednesday, May 04, 2016 02:22:22 PM Gerhard Hoffmann wrote: > Am 04.05.2016 um 10:46 schrieb Bruce Griffiths: > > Integrating A Time interval to charge TAC at the front end of a capacitive > > charge redistribution SAR ADC should allow a conversion time of 300ns or > > so.. Using 16 such TDCs should permit 1ps resolution with a 50MHz > > timestamp rate without too many cascaded gates in the selection logic for > > the next available TAC. Bruce > > One or two years ago I investigated a solution around a 16 Bit / 100 > MSPS ADC (LTC2165), a 2C64 Coolrunner, > an Avago PHEMT as current switch and a little bit of analog voodoo. That > would have fit on a 2"*2" board. > Good enough for a 10 MHz event rate, with some easy pipelining for at > least 20 MHz. > That includes the coarse counter from the last 1pps. > But we stayed with a classical time stretcher, and my private project > pipeline is already full. > > regards, Gerhard > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the > instructions there. Yes, taking advantage of the fact that one merely uses the fine time interval measurement to measure the delay of a synchroniser clocked with the same clock as the ADC makes the design relatively simple. The output of the synchroniser samples a counter clocked with the same clock as the ADC to produce the fine count. The Time to amplitude converter output is merely held for 1 or 2 clock cycles so the ADC can sample the relevant part of the output. The TAC output is then reset to zero (or better the opposite limit of the ADC input). Either a buffer is used between the TAC and ADC or a direct connection should be feasible as long as the effect of sampling during ramping of the TaC output (TAC output capacitor is being charged) is corrected for. That is correcting for the charge transfer during this undesired sample. The sample taken when the TAC is in hold being corrected for the charge transfer incurred by the sample taken during ramping. Alternatively the TAC current could be used to drrive a network with a suitable impulse response so that no explicit reset is required. The output of this network being sampled by the ADC. The fine time interval can then be recovered by curve fitting to the samples taken by the ADC.
Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
