_____________________________________________________ 1 PolaRx4_PRO and PolaRx4TR_PRO
PolaRx4 Product Family Hardware Manual v2.0.0
8
It takes a few minutes after start up to lock the clock to GNSS time. The REFOUT_LOCKED bit of the
RxState
field in the
ReceiverStatus
SBF block indicates when lock is achieved.
1.1.5
PPS IN (BNC) – PolaRx4TR_PRO Only
This connector is only available on PolaRx4TR_PRO. It is a time synchronization input (input level
3.3V CMOS with 10k
pull down resistor, 5V tolerant, V
IH
>2.3V, V
IL
<1V), to be connected to a one
pulse-per-second external reference.
Use this input to synchronize the internal receiver time to an external time source. For proper operation,
the PPS IN input should be used in combination with the REF IN input. REF IN provides the receiver
with a precise external frequency reference, and PPS IN provides a precise time reference. It is important
that the PPS input signal and the 10-MHz reference be generated from the same external clock and that
the PPS input signal be synchronized with UTC (offset with UTC smaller than 0.5 milliseconds). It is
also necessary that REF IN and PPS IN be present from the start-up of the receiver. Plugging in a PPS
input signal when the receiver is already operating will lead to erroneous measurements.
The receiver synchronizes its measurement latching with the first low-to-high transition it detects on the
PPS IN connector. There is no user command to enter. Once this initial time synchronization is done,
the signal on the PPS IN connector is ignored: the receiver simply integrates its frequency reference to
keep track of the time. If the PPS input signal originates from the same clock as the 10-MHz reference
signal, the receiver time will stay in sync with the external clock time.
The delay between a low-to-high transition on the PPS input connector and the latching of the
measurements in the receiver depends on the setup, and in particular on the phase relationship between
the 10-MHz frequency reference and the PPS input signal at the REF IN and PPS IN connectors. It can
take a value from 130.3 to 150.3 ns (+/-2 ns), as shown in the figure below.
10
0
10
1
10
2
10
3
10
-12
10
-11
10
-10
10
-9
[seconds]
s
ig
m
a
y
(
)
PolaRx4 REF OUT Allan standard deviation
