LISA-U series - System Integration Manual
UBX-13001118 - R17
Advance information
Design-In
Page 136 of 190
Digital Clock Output (CODEC_CLK)
: can be used to provide a 26 MHz or 13 MHz digital clock to an
external audio codec
Follow these hints for high speed digital pins layout:
High-speed signals become sources of digital noise, route away from RF and other sensitive analog signals
Keep routing short and minimize parasitic capacitance to preserve digital signal integrity
It is recommended to match the length of SPI signals
2.2.1.8
Digital pins and supplies
External Reset (RESET_N):
input for external reset, a logic low voltage will reset the module
SIM Card Interface (VSIM, SIM_CLK, SIM_IO, SIM_RST)
: the SIM layout may be critical if the SIM card is
placed far away from the LISA-U modules or in close proximity to the RF antenna. In the first case the long
connection can cause the radiation of some harmonics of the digital data frequency. In the second case the
same harmonics can be picked up and create self-interference that can reduce the sensitivity of GSM
Receiver channels whose carrier frequency is coincidental with harmonic frequencies. The latter case, placing
the RF bypass capacitors, suggested in the section 1.8, near the SIM connector will mitigate the problem. In
addition, since the SIM card is typically accessed by the end user, it can be subjected to ESD discharges: add
adequate ESD protection to protect module SIM pins near the SIM connector
Digital Audio (I2S_CLK
,
I2S_RX
,
I2S_TX
,
I2S_WA
and
I2S1_CLK
,
I2S1_RXD
,
I2S1_TXD
,
I2S1_WA)
: the
I
2
S interface requires the same consideration regarding electro-magnetic interference as the SIM card. Keep
the traces short and avoid coupling with RF line or sensitive analog inputs
DDC (SCL, SDA)
: the DDC interface requires the same consideration regarding electro-magnetic
interference as the SIM card. Keep the traces short and avoid coupling with RF line or sensitive analog inputs
UART (TXD, RXD, CTS, RTS, DSR, RI, DCD, DTR)
: the serial interface requires the same consideration
regarding electro-magnetic interference as the SIM card. Keep the traces short and avoid coupling with RF
line or sensitive analog inputs
General Purpose I/O (GPIOx)
: the general purpose input/output pins are generally not critical for layout
Reserved pins
: these pins are reserved for future use. Leave them unconnected on the baseboard
USB detection
(VUSB_DET)
: this input will generate an interrupt to the baseband processor for USB
detection. The USB supply (5.0 V typ.) must be provided to
VUSB_DET
by the connected USB host to enable
the USB interface of the module
Interfaces Supply
(V_INT)
: this supply output is generated by an integrated switching step down
converter, used internally to supply the digital interfaces. Because of this, it can be a source of noise: avoid
coupling with sensitive signals
