On Tue, Feb 25, 2020 at 2:00 PM Heikki Laamanen <heikki.laama...@dlc.fi> wrote:
> Thanks Brian. You are right, there exists three VCOs and PLLs in the > AD9361 which can be controlled independently. > > > > AD9361 Reference Manual UG-570 shows a more detailed diagram in Figure 7. > on page 20. The baseband PLL comprises an N/N+1 divider controlled by a > high-precision sigma-delta modulator. AD9361 Register Map Reference Manual > UG-671 describes that the control word of the sigma-delta modulator > consists of 29 bits giving a relative frequency resolution of 1.9 ppb > (parts per billion). > > > > A brief description of the timing system. The objective is a system for > protecting or replacing GPS-based timing. In addition to navigation, the > GPS system is used for generating an accurate clock which is in synchronism > with the Coordinated Universal Time (UTC). A clock synchronized with the > UTC, can be for example a 1 Hz physical clock signal whose rising edge goes > up exactly at the start of an UTC second. The accuracy of an GPS-based > timing system is about +-50 ns. Thus, we can say that the phase accuracy of > GPS-based timing is about 50 ns. The objective is to generate such clock > by receiving a broadcast radio signal which is known to be in synchronism > with the UTC. > > > > You mentioned that time is completely relative. If we think of the UTC, we > could say that it gives an absolute time which is defined by several atomic > clocks around the globe. A copy of the UTC can be generated, with a certain > accuracy, by receiving the GPS or other similar satellite signal (Galileo, > Glonass, Beidou) and synchronizing to it. > So you want to produce something like a stable 10MHz reference and a 1PPS which is synchronous to UTC using broadcast/terrestrial signals such as DVB-T, ATSC, LTE, etc? And your edges can be within +/-50ns of actual UTC? I guess I'm still unsure if you do or do not believe the radios out there allow for this to happen? I'm not sure where you believe you have a limitation. Brian
