Hi I think the tradeoff of "harmonics still better than -60dbc" is fine if the floor does indeed drop a few more db. For time nut applications, it's going to be the phase noise close to carrier that matters. Harmonics with reasonable terminations would not be the big issue.
It will be interesting to see if the supplies really do contribute to the close in noise in this case. If so, there are a lot of ways to take care of that. My guess is that a couple simple linear regulators will take care of it if there's an issue there. If you have a setup to do so, take a look at the output return loss next time it's up and running. One thing this approach *should* do is to give you very good return loss. Bob -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Tuesday, February 28, 2012 1:21 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] OP-Amps for 10MHz distribution...? The datasheet indicates that an input of +13dBm should be OK albeit with somewhat more 3rd harmonic distortion (~-65dBc) in the output. I'll unearth the prototype single transistor (2N5943) transformer feedback discrete buffer and use it to boost the signal before the splitter. I'll also measure its phase noise, or at least attempt to do so as its likely to be very quiet. The OPA653 was mounted on the TI evaluation board using its internal feedback resistors to set the gain to 2x before the 2x attenuation produced by the source termination and load resistors. The board was powered by a couple of HP E3611A bench supplies. Its likely that the low frequency power supply noise modulation of internal opamp capacitances (and hence the output phase) is greater than that due to opamp noise. Measurements with quieter power supplies may be useful. The OPA653 is a voltage feedback amplifier, a current feedback amp like the AD8007 is likely to have a somewhat higher phase noise floor (+6dB) due to the inverting input noise current (22.5pA/rtHz) flowing in the feedback network resistors (2 x 500 ohm for a gain of 2 ). Bruce Bob Camp wrote: > Hi > > Very cool. How much power can you run through the device? Put another way, if you drive it with +13 dbm do all the numbers get 5 db better? > > I doubt very many of us will be worrying about weather it's below -153 at 10 Hz or not. > > Bob > > > On Feb 28, 2012, at 5:42 AM, Bruce Griffiths wrote: > > >> The attached plot indicates the phase noise performance obtainable with a wideband FET (OPA653) input opamp. >> With a 10MHz +9dBm input, the phase noise floor is around -163dBc/Hz at 1kHz offset and around -154dBc/Hz at 10Hz offset. >> A quieter test source would be useful particularly for offsets below 10Hz. >> >> Bruce >> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
