Board Description

More detailed description of LimeSDR XTRX board components and interconnections is given in the following sections of this chapter.

LMS7002M RF transceiver digital connectivity

The interface and control signals are described below:

• Digital Interface Signals: LMS7002 is using data bus LMS_DIQ1_D[11:0] and LMS_DIQ2_D[11:0], LMS_EN_IQSEL1 and LMS_EN_IQSEL2, LMS_FCLK1 and LMS_FCLK2, LMS_MCLK1 and LMS_MCLK2 signals to transfer data to/from the XILINX FPGA. Indices 1 and 2 indicate transceiver digital data PORT-1 or PORT-2. Any of these ports can be used to transmit or receive digital IQ data. By default PORT-1 is selected as transmitter port and PORT-2 is selected as receiver port. The FCLK# is input clock and MCLK# is output clock for the LMS7002M transceiver. TXNRX signals are used to indicate ports direction. Please refer to LMS7002M transceiver datasheet page 12-13. [link] for the LMS7002M interface timing.

• LMS Control Signals: these signals are used for the following functions within the LMS7002 RFIC: * LMS_RXEN, LMS_TXEN – receiver and transmitter enable/disable signals connected to FPGA Bank 14 (3.3V). * LMS_RESET – LMS7002M reset is connected to FPGA Bank 14 (3.3V).

• SPI Interface: LMS7002M transceiver is configured via 4-wire SPI interface: FPGA_SPI_SCLK, FPGA_SPI_MOSI, FPGA_SPI_MISO, FPGA_SPI_LMS_SS. The SPI interface is connected to FPGA Bank 14 (3.3V).

• LMS I2C Interface: can be used for LMS EEPROM content modification or debug purposes. The signals LMS_I2C_SCL and LMS_I2C_DATA are connected to EEPROM.

Table 1. LMS7002M RF transceiver digital interface pins

Chip pin (IC1)	Chip reference (IC1)	Schematic signal name	FPGA pin	FPGA I/O standard	FPGA I/O standard
E5	xoscin_tx	LMS_TX_CLK			Connected to 26.00 MHz clock
AB34	MCLK1	LMS_MCLK1	L17	3.3V
AA33	FCLK1	LMS_FCLK1	G19	3.3V
V32	TXNRX1	LMS_TXNRX1	V15	3.3V
U29	TXEN	LMS_TXEN	W19	3.3V
Y32	ENABLE_IQSEL1	LMS_EN_IQSEL1	P19	3.3V
AG31	DIQ1_D0	LMS_DIQ1_D0	J17	3.3V
AF30	DIQ1_D1	LMS_DIQ1_D1	H17	3.3V
AF34	DIQ1_D2	LMS_DIQ1_D2	H19	3.3V
AE31	DIQ1_D3	LMS_DIQ1_D3	K17	3.3V
AD30	DIQ1_D4	LMS_DIQ1_D4	G17	3.3V
AC29	DIQ1_D5	LMS_DIQ1_D5	V16	3.3V
AE33	DIQ1_D6	LMS_DIQ1_D6	J19	3.3V
AD32	DIQ1_D7	LMS_DIQ1_D7	M19	3.3V
AC31	DIQ1_D8	LMS_DIQ1_D8	P17	3.3V
AC33	DIQ1_D9	LMS_DIQ1_D9	N19	3.3V
AB30	DIQ1_D10	LMS_DIQ1_D10	U17	3.3V
AB32	DIQ1_D11	LMS_DIQ1_D11	U16	3.3V
AM24	xoscin_rx	LMS_TX_CLK			Connected to 26.00 MHz clock thru 0R (NF)
P34	MCLK2	LMS_MCLK2	W5	3.3V
R29	FCLK2	LMS_FCLK2	W6	3.3V
U31	TXNRX2	LMS_TXNRX2	U5	3.3V
V34	RXEN	LMS_RXEN	W18	3.3V
R33	ENABLE_IQSEL2	LMS_EN_IQSEL2	W7	3.3V
H30	DIQ2_D0	LMS_DIQ2_D0	W2	3.3V
J31	DIQ2_D1	LMS_DIQ2_D1	U2	3.3V
K30	DIQ2_D2	LMS_DIQ2_D2	U3	3.3V
K32	DIQ2_D3	LMS_DIQ2_D3	V3	3.3V
L31	DIQ2_D4	LMS_DIQ2_D4	V4	3.3V
K34	DIQ2_D5	LMS_DIQ2_D5	V2	3.3V
M30	DIQ2_D6	LMS_DIQ2_D6	V5	3.3V
M32	DIQ2_D7	LMS_DIQ2_D7	V4	3.3V
N31	DIQ2_D8	LMS_DIQ2_D8	V8	3.3V
N33	DIQ2_D9	LMS_DIQ2_D9	U4	3.3V
P30	DIQ2_D10	LMS_DIQ2_D10	U8	3.3V
P32	DIQ2_D11	LMS_DIQ2_D11	U7	3.3V
U33	CORE_LDO_EN	LMS_CORE_LDO_EN	W17	3.3V
E27	RESET	LMS_RESET	U19	3.3V
D28	SEN	FPGA_SPI_LMS_SS	W13	3.3V	SPI interface
C29	SCLK	FPGA_SPI_SCLK	W14	3.3V	SPI interface
F30	SDIO	FPGA_SPI_MOSI	W16	3.3V	SPI interface
F28	SDO	FPGA_SPI_MISO	W15	3.3V	SPI interface
D26	SDA	LMS_I2C_SDA			Connected to EEPROM
C27	SCL	LMS_I2C_SCL			Connected to EEPROM

RF network control signals

LimeSDR XTRX RF network contains matching networks, RF switches, loopback variable attenuator and U.FL connectors (X1, X3 - TX and X2, X4 - RX) as shown in Figure 1.

Figure 1. LimeSDR XTRX v1.2 RF diagram

LMS7002M RF transceiver TX and RX ports has dedicated matching network which determines the working frequency range. More detailed information on LMS7002M RF transceiver ports and matching network frequency ranges is listed in the Table 2.

Table 2. LMS7002M RF transceiver ports and matching networks frequency ranges

LMS7002M RF transceiver port	Frequency range
TX1_1, TX2_1	2 GHz - 2.6 GHz
TX1_2, TX2_2	30 MHz - 1.9 GHz
RX1_H, RX2_H	2 GHz - 2.6 GHz
RX1_W, RX2_W	700 MHz - 900 MHz
RX1_L, RX2_L	300 MHz – 2.2 GHz

RF network switches are controlled via 2.4V logic signals. This is achieved by resistor dividers connected between FPGA (TX_SW, RX_SW1, RX_SW2) and switch control pin (TX_SW_DIV, RX_SW1_DIV, RX_SW2_DIV). RF network control signals are described in the Table 3.

Table 3. RF network control signals

Component	Schematic signal name	I/O standard	FPGA pin	Description
SKY13330-397LF(IC5 and IC6)	TX_SW/TX_SW_DIV	3.3V	P1	FPGA 3.3V logic level signal divided to 2.4V logic level.
SKY13414-485LF(IC3 and IC4)	RX_SW1/RX_SW1_DIV	3.3V	K3	FPGA 3.3V logic level signal divided to 2.4V logic level.
	RX_SW2/RX_SW2_DIV	3.3V	J3	FPGA 3.3V logic level signal divided to 2.4V logic level.

LMS7002M baseband connectors

LMS7002M RF transceiver (IC1)) baseband signals (RX ADC and TX DAC) can be accessed via 0.3mm pitch 15 pin FPC connectors (X13 and X8). RX DAC connector pinout is shown in Table 4. TX ADC connector pinout is shown in Table 5.

Table 4. LMS7002 base band TX DAC connector (X13)

Pin	Schematic signal name	Description
1	GND	Ground
2	DAC1Q_P	Channel 1 quadrature signal differential positive
3	DAC1Q_N	Channel 1 quadrature signal differential negative
4	GND	Ground
5	DAC1I_P	Channel 1 in-phase signal differential positive
6	DAC1I_N	Channel 1 in-phase signal differential negative
7	GND	Ground
8	GPIO13	General purpose input/output (FPGA pin T17)
9	GND	Ground
10	DAC2Q_P	Channel 2 quadrature signal differential positive
11	DAC2Q_N	Channel 2 quadrature signal differential negative
12	GND	Ground
13	DAC2I_P	Channel 2 in-phase signal differential positive
14	DAC2I_N	Channel 2 in-phase signal differential negative
15	GND	Ground

Table 5. LMS7002 base band RX ADC connector (X8)

Pin	Schematic signal name	Description
1	GND	Ground
2	ADC1I_P	Channel 1 in-phase signal differential positive
3	ADC1I_N	Channel 1 in-phase signal differential negative
4	GND	Ground
5	DAC1Q_P	Channel 1 quadrature signal differential positive
6	DAC1Q_N	Channel 1 quadrature signal differential negative
7	GND	Ground
8	GPIO13	General purpose input/output (FPGA pin T17)
9	GND	Ground
10	ADC2I_P	Channel 2 in-phase signal differential positive
11	ADC2I_N	Channel 2 in-phase signal differential negative
12	GND	Ground
13	ADC2Q_P	Channel 2 quadrature signal differential positive
14	ADC2Q_N	Channel 2 quadrature signal differential negative
15	GND	Ground

USB 2.0 controller

LimeSDR XTRX could be powered and programmed via USB 2.0 by connecting it to micro-B port or mini PCIe connector. USB 2.0 is implemented using Microchip USB3333E-GL transceiver [link]. The controller signals description are shown below:

• USB_D[7:0] – 8-bit data interface is connected to FPGA.

• USB_NRST, USB_NXT, USB_DIR, USB_STP – interface control signals.

• USB_CLK – interface clock. Clock from transceiver is fed to XILINX FPGA.

• USB_26M – interface clock. Clock from FPGA is fed to Lime transceiver.

USB 2.0 controller pins, schematic signal names, FPGA interconnections and I/O standard are described in Table 6.

Table 6. USB 2.0 controller interface

Chip pin (IC19)	Chip reference (IC19)	Schematic signal name	FPGA pin	I/O standard
C2	RESETB	USB_NRST	M18	3.3V
E3	DAT7	USB_D7	C15	3.3V
E4	DAT6	USB_D6	A14	3.3V
E5	DAT5	USB_D5	A15	3.3V
D4	DAT4	USB_D4	B15	3.3V
D5	DAT3	USB_D3	A16	3.3V
C4	DAT2	USB_D2	B16	3.3V
C5	DAT1	USB_D1	A17	3.3V
B4	DAT0	USB_D0	B17	3.3V
A3	STP	USB_STP	C17	3.3V
B5	NXT	USB_NXT	A18	3.3V
A4	DIR	USB_DIR	B18	3.3V
A5	CLKOUT	USB_CLK	C16	3.3V
A2	REFCLK	USB_26M	E19	3.3V

Indication LEDs

LimeSDR XTRX board comes with two green indicator LEDs. These LEDs are soldered on the top of the board near the USB Micro-B connector.

Figure 2. LimeSDR XTRX indication LEDs (top)

LEDs are connected to FPGA hence their function may be programmed according to the user requirements. Default LEDs configuration and description are shown in Table 7.

Table 7. Default LEDs configuration

Board Reference	Schematic name	Board label	FPGA pin	Description
LED1	FPGA_LED1	LED1	N18	User defined
LED2	FPGA_LED2	LED2	V19	User defined

Low speed interfaces

FPGA_SPI pins, schematic signal names, FPGA interconnections and I/O standards/levels are shown in Table 8.

Table 8. FPGA_SPI interface pins

Schematic signal name	FPGA pin	I/O standard	Comment
FPGA_SPI_SCLK	W14	3.3V	Serial Clock (FPGA output)
FPGA_SPI_MOSI	W16	3.3V	Data (FPGA output)
FPGA_SPI_MISO	W15	3.3V	Data (FPGA input)
FPGA_SPI_LMS_SS	W13	3.3V	IC1 (LMS7002 (IC1)) SPI slave select (FPGA output)

FPGA_CFG_SPI pins, schematic signal names, FPGA interconnections and I/O standards are shown in Table 9.

Table 9. FPGA_CFG_SPI interface pins

Schematic signal name	FPGA pin	I/O standard	Comment
FPGA_CFG_CCLK	C11	3.3V	Serial Clock (FPGA output)
FPGA_CFG_CS	K19	3.3V	IC18 SPI slave select (FPGA output)
FPGA_CFG_D00	D18	3.3V
FPGA_CFG_D01	D19	3.3V
FPGA_CFG_D02	G18	3.3V
FPGA_CFG_D03	F18	3.3V

FPGA_I2C1 (temperature sensor, EEPROM, CLK DAC, switching regulator) and FPGA_I2C2 (switching regulator) interface slave devices and related information are given in Table 10.

Table 10. FPGA_I2C1 and FPGA_I2C2 interfaces pins

I2C slave device	Slave device	Inteface	I2C address	I/O standard	Comment
IC9	Temperature sensor	FPGA_I2C1	1 0 0 1 0 1 1 RW	3.3V	TMP1075NDRLR
IC13	EEPROM		1 0 1 0 0 0 0 RW	3.3V	M24128
IC17	CLK DAC		1 0 0 1 1 0 0 RW	3.3V	AD5693RACPZ
IC22	Switching regulator		1 1 0 0 0 0 0 RW	3.3V	LP8758A1E0YFFR
IC31	Switching regulator	FPGA_I2C2	1 1 0 0 0 0 0 RW	3.3V	LP8758A1E0YFFR

To debug FPGA design, flash bitstream to FPGA and/or Flash memory JTAG X9 connector is used. It is located on the PCB bottom side (see Figure 5: LimeSDR XTRX v1.2 board bottom connectors and main components) and is compatible with Molex 788641001 connector. JTAG connector pins, schematic signal names, FPGA interconnections and I/O standards are listed in Table 11.

Table 11. JTAG connector X9 pins

Connector pin	Schematic signal name	FPGA pin	I/O standard	Comment
1	TDO	W8	3.3V	Test Data Out
2	TDI	W10	3.3V	Test Data In
3	TMS	W9	3.3V	Test Mode Select
4	VCC3P3			Power (3.3V)
5	TCK	C8	3.3V	Test Clock
6	GND			Ground

GPIO connectors

Four GPIOs from FPGA are connected to 8 pin FPC connector (X12). GPIOS are separated by ground pins. Additional pin is dedicated for power as shown in Table 12.

Table 12. FPGA GPIO connector (X12) pins

Connector pin	Schematic signal name	FPGA pin	I/O standard	Comment
1	VCC3P3		3.3V	Power (3.3V)
2	GPIO9_P	H1	3.3V
3	GND		3.3V	Ground
4	GPIO9_N	J1	3.3V
5	GND		3.3V	Ground
6	GPIO11_P	K2	3.3V
7	GND		3.3V	Ground
8	GPIO11_N	L2	3.3V

Clock Distribution

LimeSDR XTRX board clock distribution block diagram is as shown in Figure 3.

Figure 3. LimeSDR XTRX v1.2 board clock distribution block diagram

LimeSDR XTRX board features an on board 26.00 MHz VCTCXO as the reference clock for LMS7002M RF transceiver and FPGA PLLs.

Rakon E6982LF 26.00 MHz voltage controlled temperature compensated crystal oscillator (VCTCXO) is the clock source for the board. VCTCXO frequency may be tuned by using 16 bit DAC (IC17). Main VCTCXO parameters are listed in Table 13.

Table 13. Rakon E6982LF VCTCXO main parameters

Frequency parameter	Value
Calibration (25°C ± 1°C)	± 1 ppm max
Stability (-40 to 85 °C)	± 0.2 max
Long term stability (1 year, 3 years)	± 1 ppm max, ± 2 ppm max
Control voltage range	0.5V .. 2.8V
Frequency tuning	± 3 ppm
Slope	+4 ppm/V

Analogue switch gives option to select clock source for RF transceiver and FPGA from buffered VCTCXO onboard clock XO1 (CLK_XO) and external U.FL (X7)/mPCIe (X10) sources (CLK_IN_BUFF). Buffered VCXO clock (CLK_OUT) can also be fed to other board using U.FL (X7)/mPCIe (X10)connectors.

The board clock lines and other related signals/information are listed in Table 14. VCCIO_CLK voltage can be selected between 1.8V and 3.3V (default).

Table 14. LimeSDR XTRX main clock lines

Source	Schematic signal name	I/O standard	FPGA pin	Description
External	CLK_IN	VCCIO_CLK		External reference clock input
Clock buffer (IC10)	CLK_OUT	VCCIO_CLK		Reference clock output
Clock buffer (IC14)	FPGA_CLK	3.3V	A9	Reference clock connected to FPGA
Analog mux (IC15)	CLK_XO	1.8V		Reference clock connected to LMS
RF transceiver (IC1)	LMS_TX_CLK	1.8V		Reference clock input
	LMS_TX_CLK	1.8V		Reference clock input (0R)
	LMS_MCLK1	3.3V	L17
	LMS_FCLK1	3.3V	G19
	LMS_MCLK2	3.3V	W5
	LMS_FCLK2	3.3V	W6
USB 2.0 controller (IC19)	USB_CLK	3.3V	C16	Clock output from USB controller
	USB_26M	3.3V	E19	Clock input for USB controller
GNSS Receiver (IC11)	GNSS_1PPS	3.3V	P3	PPS output from GNSS receiver to FPGA
FPGA (IC7)	1PPSI_GPIO1(1N)	3.3V	M3	FPGA PPS input
FPGA (IC7)	1PPSO_GPIO2(1P)	3.3V	L3	PPS output from FPGA to X6 ND mPCIe pin 5
External	1PPS_IN	3.3V	M3	PPS input for FPGA

Power Distribution

As indicated, LimeSDR XTRX board may be powered via USB port (5V) or mini PCIe edge connector (3.3V). LimeSDR XTRX board power delivery network consists of different power rails/voltages, filters and power sequences. LimeSDR XTRX board power distribution block diagram is presented in Figure 4.

Figure 4. LimeSDR XTRX v1.2 board power distribution block diagram

Mini PCIe edge connector

LimeSDR XTRX board communicates with the host system via mPCIe connector. LimeSDR XTRX mini PCIe connector pinout and signals according to the specification is given in Table 15.

Table 15. Mini PCIe x1 edge connector pinout

Pin	Mini PCIe x1 Specification	LimeSDR XTRX Schematic signal name	Description
1	Wake#	NC	Not connected
2	3.3 Vaux	VCC3P3_MPCIE	Main power input 3.3V (VCC3P3_MPCIE)
3	COEX1	1PPSI_GPIO1(1N)	External 1PPS input or GPIO1 or GPIO1N, CMOS 3.3 V
4	GND	GND	Ground
5	COEX2	1PPSO_GPIO2(1P)	GPS 1PPS output or GPIO2 or GPIO1P, CMOS 3.3 V
6	GND	NC	Not connected
7	CLKREQ#	CLK_REQUEST#	Tied to GND through resistor 330 Ohm
8	UIM PWR	UIM_VCC	User Identity Module interface power 1.8 V or 3V
9	GND	GND	Ground
10	UIM_DATA	UIM_DIO	User Identity Module interface data 1.8 V or 3V
11	REFCLK-	PCI_REF_CLK_N	PCI Express Reference clock differential pair negative signal
12	UIM_CLK	UIM_CLK	User Identity Module interface clock 1.8 V or 3V
13	REFCLK+	PCI_REF_CLK_P	PCI Express Reference clock differential pair positive signal
14	UIM_RESET	UIM_RST	User Identity Module interface reset 1.8 V or 3V
15	GND	GND	Ground
16	UIM_VPP	NC	Not connected
17	Reserved	TDD_GPIO3_N	TDD TX Enable output or GPIO3N or GPIO4, CMOS 3.3V
18	GND	GND	Ground
19	Reserved	CLK_IN	External clock input 3.3 V
20	W_DISABLE#	TDD_GPIO3_P	GPIO3P or GPIO3 (or Pair of TDD TX Enable), CMOS 3.3V
21	GND	GND	Ground
22	PERST#	PCIE_PERST#	PCI Express interface reset
23	PERn0	PCI_TX0_N	PCI Express interface output differential pair negative signal
24	3.3Vaux	NC	Not connected
25	PERp0	PCI_TX0_P	PCI Express interface output differential pair positive signal
26	GND	GND	Ground
27	GND	GND	Ground
28	1.5Volt	NC	Not connected
29	GND	GND	Ground
30	SMB CLK	SMB_CLK	Clock output (CLK_OUT)
31	PETn0	PCI_RX0_N	PCI Express interface input differential pair negative signal
32	SMB Data	SMB_DATA	GPIO8
33	PETp0	PCI_RX0_P	PCI Express interface input differential pair positive signal
34	GND	GND	Ground
35	GND	GND	Ground
36	USB_D-	USB_D_N	USB 2.0 data differential pair negative signal
37	GND	GND	Jumper to GND. Connected by default
38	USB_D+	USB_D_P	USB 2.0 data differential pair positive signal
39	3.3Vaux	PCI_TX1_N	PCI Express interface output differential pair negative signal
40	GND	GND	Ground
41	3.3Vaux	PCI_TX1_P	PCI Express interface output differential pair positive signal
42	LED_WWAN#	LED_WWAN#_GPIO5	Output for LED WWAN (Negative) or GPIO5 3.3 V
43	GND	GND	Jumper to GND. Connected by default
44	LED_WLAN#	LED_WLAN#_GPIO6	Jumper to GND. Connected by default
45	Reserved	PCIE_RESERVED	Connected to FPGA (V7)
46	LED_WPAN#	LED_WPAN#_GPIO7	Output for LED WPAN (Negative) or GPIO7 3.3 V
47	Reserved	PCI_RX1_N	PCI Express interface input differential pair negative signal
48	1.5Volt	NC	Not connected
49	Reserved	PCI_RX1_P	PCI Express interface input differential pair positive signal
50	GND	GND	Ground
51	Reserved	PCIE_W_DISABLE2#	Connected to FPGA (W3)
52	3.3Vaux	VCC3P3_MPCIE	Main power input 3.3V (VCC3P3_MPCIE)