Lime-GPSDO v1.0 hardware description

Lime-GPSDO Board Key Features

The Lime-GPSDO development board provides high stability clock source for timing sensitive applications. Clock frequency is being constantly monitored inside MAX10 FPGA and tuned by PPS signal from GNSS module.

Lime-GPSDO v1.0

For more information on the following topics, refer to the respective documents:

• MAX10 device family, refer to Intel documentation link
• N20B GNSS module resources link

Lime-GPSDO board features:

• USB Interface
  • Silicon labs USBXpress Family USB-to-UART bridge CP2102N.
• FPGA Features
  • MAX10 10M16SAU169C8 device in 169-pin UBGA
  • 16K logic elements
  • 549 Kbits embedded memory (M9K) and 2368 Kbits of user Flash Memory
  • 45 embedded 18x18 multipliers
  • 1 PLLs
• FPGA Configuration
  • JTAG mode configuration
• Memory Devices
  • 4Mbit FLASH
  • 128Kbit (16K x 8) EEPROM
• Connections
  • microUSB2.0 (type B)
  • SMA connectors for clock IN/OUT, time pulse output and GNSS antenna
  • FPGA GPIO header (0.05” pitch)
  • FPGA JTAG connectors (0.05” pitch and side connector)
  • 5V DC power jack and pinheader
  • Backup battery connector for GNSS receiver
  • Clock output pinheader
  • External UART connector
  • External I2C connector
• Clock System
  • 30.72MHz VCOCXO:
    • Frequency calibration ±0.5ppm;
    • Frequency stability over temperature in still air ±20ppb;
    • Frequency slope ΔF/ΔT in still air ±1.2ppb/°C
  • Possibility to tune VCOCXO by onboard DAC
  • Possibility to use GNSS PPS signal as a reference when tuning VCOCXO frequency
• Board Size without connectors 50.50mm x 80mm (1.99” x 3.15”)

Board Overview

Lime-GPSDO board version 1.0 picture with highlighted major components and connections presented in Figure 1 and Figure 2. There are three connector types – data and debugging (USB2.0, FPGA GPIO and JTAG), power (DC jack and external supply pinheader), clock source output, GNSS antenna and time pulse output.

Figure 1 Lime-GPSDO top side components and connectors

Figure 2 Bottom side components

Board components description listed in the Table 1 and Table 2.

Table 1. Board components

Featured Devices
Board reference	Type	Description
IC5	GNSS module	GNSS receiver
IC5	FPGA	Intel MAX 10 (10M16SAU169C8G 169-UBGA)
IC9	USB UART	Silicon labs USB-to-UART bridge
Miscellaneous devices onboard
IC13	IC	Temperature sensor LM75
Configuration, Status and Setup Components
J9	JTAG chain pin header	FPGA programming pin header for Altera USB-Blaster download cable, side connection.
J10	JTAG chain pin header	FPGA programming pin header for Altera USB-Blaster download cable, 0.05” pitch
LEDS1, LEDS2, LEDS3	Red-green status LEDs	User defined FPGA indication.
General User Input/Output
J12	Pin header	8 FPGA GPIOs plus 2 power pins, 0.05” pitch
SW1	Slide switch	4 slide switches connected to FPGA
SW2	Push button	Push button connected to FPGA
Memory Devices
IC11	EEPROM	128K (16K x 8) EEPROM connected to FPGA
IC10	IC	I²C EEPROM Memory 128Kb (16K x 8), connected to FPGA I2C bus
IC7	Flash memory	4Mbit FLASH memory connected to FPGA
Communication Ports
J11	USB2.0 connector	microUSB2.0 (type B) connector
J8	Header	GNSS USB 2.0 connection header (unused)
J15	Header	External UART interface header, can be used to control external periphery. Additional logic has to be implemented in FPGA.
J16	Header	External I2C interface header, can be used to control external periphery. Additional logic has to be implemented in FPGA.
Clock Circuitry
XO1	VCOCXO	30.72MHz voltage-controlled crystal oscillator used as a reference clock.
XO2	XO	50MHz crystal oscillator, used for FPGA logic.
IC2	DAC	Analog devices 16bit Digital-to-analog converter for VCOCXO voltage control
J1	Pin header	Optional clock output of XO1
J2	Pin header	Optional Voltage control input for XO1
J3	SMA connector	Time pulse output from GNSS modules
J5	SMA connector	Reference clock output
J6	U.FL connector	Reference clock output, connector is not fitted by default.
Power Supply
J14	DC input jack	External 5V DC power supply
J13	Pin header	External 5V DC power supply and main internal power rail
Other
J4	SMA connector	Antenna input for GNSS module
J7	Pin header	Backup battery connection header for GNSS module. Typical 3.0V (follow recommendation in fitted GNSS module datasheet)