hi zhu yan and michael, to bring the roach2 sync output voltage down to 0 to 5 volts when driving 50 ohms, you could use a connectorized 50 ohm 3 dB attenuator.
a 3 dB attenuator should lower the voltage from 0 to 7 volts, down to 0 to 5 volts. best wishes, dan On Thu, May 18, 2017 at 1:31 AM, Zhu, Yan <zhu...@nao.cas.cn> wrote: > Hi Michael and all, > > I'm also intended to use sync_out or other GPIO to output square wave to > control noise source, > I measured 6V for sync_out and GPIO pin 1.5V. > > After digging into ROACH2 schematics(page 25 in > roach2_rev2_schematics.pdf), > I found the differential signal is first converted into single ended by > SN65LVDT2 > than > buffered out by THS3091. The THS3091 is given a 12V supply. > After a quick look at THS3091 datasheet, it will output about 12V at > 50Ohm load with 15V VS > and 3V with 5V VS, so 6~7V output is reasonable for 12V power supply(a > little lower than expect?). > > Can anyone remember why pull the sync_out that high instead of normal TTL > or CMOS level? > If I want to use it to drive a load which expect TTL or CMOS level, how > should I connect them? > > > Thanks > Yan > > > > > > ------ Original Message ------ > From: "Michael D'Cruze" <michael.dcr...@postgrad.manchester.ac.uk> > To: "casper@lists.berkeley.edu" <casper@lists.berkeley.edu> > Sent: 2017-05-12 02:10:26 > Subject: [casper] ROACH2 sync_out > > Dear all, > > > > I’m planning to use a 0.5Hz square wave, generated from the FPGA and > output via sync_out, to eventually fire our cal diode (via much cabling). A > quick hardware test today shows the sync_out port driving at circa 7V (!). > This is a bit higher than I was expecting. Does this venture as a whole > seem like a particularly bad idea to anyone with experience using sync_out? > Is this output voltage roughly as expected? > > > > Thanks a lot, > > Michael > > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To post to this group, send email to casper@lists.berkeley.edu. > > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To post to this group, send email to casper@lists.berkeley.edu. > -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu" group. To unsubscribe from this group and stop receiving emails from it, send an email to casper+unsubscr...@lists.berkeley.edu. To post to this group, send email to casper@lists.berkeley.edu.
