EVA-8M and EVA-M8 series - Hardware Integration Manual
UBX-16010593 - R06
Design-in
Page 14 of 47
Early Production Information
2.3.3.2
3-pin antenna supervisor
The 3-pin antenna supervisor is comprised of the
ANT_DET
(active antenna detection),
ANT_OK
(short detection) and
ANT_OFF
(antenna on/off control) pins. This function must be activated by
sending the following sequence to the EVA-8M / EVA-M8 series receivers in production:
•
B5 62 06 41 0C 00 00 00 03 1F CD 1A 38 57 FF FF F6 FF DE 11
☞
Applying this sequence results in a permanent change and cannot be reversed. An unstable supply
voltage at the
VCC_IO
pin while applying this sequence can also damage the receiver.
Function
I/O
Description
Remarks
ANT_DET
I
(pull-up)
Antenna detected
“high” = Antenna detected
“low” = Antenna not detected
Byte sequence given in section 2.3.3.2
should be applied.
ANT_OK
I
(pull-up)
Antenna not shorted
“high” = antenna has no short
“low” = antenna has a short
Byte sequence given in section 2.3.3.2
should be applied.
ANT_OFF
O
Control signal to turn on and off the antenna
supply
“high” = turn off antenna supply
“low” = short to GND
Byte sequence given in section 2.3.3.2
should be applied.
Table 4: 3-pin Antenna supervisor pins
The external circuitry, as shown in Appendix A.8, (see Figure 20) provides detection of an active
antenna connection status. If the active antenna is present, the DC supply current exceeds a preset
threshold defined by R4, R5, and R6. It will shut down the antenna via transistor T1 if a short circuit
has been detected via U7 or if it
’
s not required (e.g. in Power Save Mode).
The status of the active antenna can be checked by the UBX-MON-HW message. More information
see the
u-blox 8 / u-blox M8 Receiver Description Including Protocol Specification [3].
The open drain buffers U4, U7 and U8 (e.g. Fairchild NC7WZ07) are needed to shift the voltage levels.
R3 is required as a passive pull-up to control T1 because U4 has an open drain output. R4 serves as a
current limiter in the event of a short circuit.
2.3.4
Electromagnetic interference and I/O lines
Any I/O signal line (length > ~3 mm) can act as an antenna and may pick up arbitrary RF signals
transferring them as noise into the GNSS receiver. This specifically applies to unshielded lines, lines
where the corresponding GND layer is remote or missing entirely, and lines close to the edges of the
printed circuit board. If for example, a cellular signal radiates into an unshielded high-impedance line,
it is possible to generate noise in the order of volts and not only distort receiver operation but also
damage it permanently.
On the other hand, noise generated at the I/O pins will emit from unshielded I/O lines. Receiver
performance may be degraded when this noise is coupled into the GNSS antenna (see Figure 9).
In case of improper shielding, it is recommended to use resistors or ferrite beads (see Appendix B.12)
on the I/O lines in series. These components should be chosen with care because they will affect also
the signal rise times. Alternatively, feed-thru capacitors with good GND connection close to the GNSS
receiver can be used (see Appendix B.13).
EMI protection measures are particularly useful when RF emitting devices are placed next to the
GNSS receiver and/or to minimize the risk of EMI degradation due to self-jamming. An adequate
layout with a robust grounding concept is essential in order to protect against EMI. More information
can be found in subsection 2.13.6.3.
