i think matt is right about the sync output voltages and impedance. the roach2 sync output should be about 0 to 6 volts with no load, and about 0 to 3 volts when this signal is terminated in 50 ohms.
so no attenuator is needed if the sync signal is connected to a 50 ohm load. if the device that is receiving the sync signal doesn't have a 50 ohm input, then matt's suggestion of adding an inline connectorized 50 ohm terminator, or using a T and 50 ohm termination resistor will get the voltage to CMOS/TTL levels. best wishes, dan On Thu, May 18, 2017 at 1:31 AM, Zhu, Yan <[email protected]> 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" <[email protected]> > To: "[email protected]" <[email protected]> > 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 " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > > -- > You received this message because you are subscribed to the Google Groups " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > -- You received this message because you are subscribed to the Google Groups "[email protected]" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected].
