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Ubuntu-enabled open source SDR board shrinks in size and price

Sep 15, 2017 — by Rick Lehrbaum — 2,271 views
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Lime Microsystems launched the $139 “LimeSDR Mini,” a size- and cost-reduced sibling of its Ubuntu Core-enabled LimeSDR board, at Crowd Supply.

Lime Microsystems, a developer of field programmable RF (FPRF) transceivers for wireless broadband systems, has gone to Crowd Supply again, to fund a size- and cost-reduced variant of the LimeSDR board that it launched there last year. Like its larger sibling, the LimeSDR Mini is a “free and open source project” that supports the company’s “entirely open-source” LimeSuite host-side software that supports a range of SDRs.



Original LimeSDR (left) compared to LimeSDR Mini
(click image to enlarge)

At 69 x 31.4mm, the LimeSDR Mini is about one-third the size of the original model, and is not meant to replace it. “Rather, they are complementary,” says the project’s Crowd Supply campaign page.


LimeSDR Mini front (left) and back renders
(click images to enlarge)

The LimeSDR Mini targets the same types of applications as the original model: low-cost, multi-protocol cellular base stations and IoT gateways. Supported wireless protocols and communication standards similarly include UMTS, LTE, GSM, WiFi, LoRa, Bluetooth, Zigbee, RFID, Digital Broadcasting, among many others.

The Mini’s reduced size and cost resulted from implementing a subset of the original LimeSDR board’s features. Specifically, the Mini has a reduced frequency range, RF bandwidth, and sample rate, half as many receive and transmit channels, and significantly fewer programmable logic gates. The key specs of both boards are tabulated below, and more detailed specs for the Mini are listed farther below.


Comparison of LimeSDR and LimeSDR Mini Key Specs

LimeSDR LimeSDR Mini
Frequency range 100KHz – 3.8GHz 10MHz – 3.5GHz
RF bandwidth 61.44MHz 30.72MHz
Sample depth 12-bit
Sample rate 61.44MSPS 30.72MSPS
TX channels 2 1
RX channels 2 1
Duplex Full
Interface 1x USB 3.0
Prog. logic gates 40k 16K
Chipset LMS7002M
Oscillator precision +/-1 ppm initial,
+/- 4 ppm stable
Transmit power 10 dBm max.
(depends on freq.)
Open source Full
Dimensions 100 x 60mm 69 x 31.4mm
Price $299 $139


The two LimeSDR siblings are also very similar architecturally, as indicated by their respective block diagrams, below.


Block diagrams of original LimeSDR (left) and LimeSDR Mini
(click images to enlarge)

As in the case of its predecessor, the LimeSDR Mini’s FPGA manages DSP and interfacing tasks, while a USB 3.0-connected host system running Snappy Ubuntu Core provides user interface and various high-level supervisory functions. With Snappy Ubuntu Core’s built-in support for an app marketplace, LimeSDR apps can easily be downloaded, installed, developed, and shared. Additionally, the board’s host driver architecture supports both the SoapySDR and UHD APIs, providing further flexibility of application development.


LimeSDR Mini enclosure prototype and its pair of antennas
(click images to enlarge)

The LimeSDR Mini’s on-board firmware supports advanced features such as timed TX bursts and RX sample timestamps, “as required for use with GSM and other time-sensitive protocols,” says the project. The LimeSDR drivers that run on the host system under Ubuntu are built with a “Lime Suite” library that’s said to handle programming and calibration of the LimeSDR board’s LMS7002M FPRF transceiver, as well as other low-level functions.

Specifications listed for the LimeSDR Mini board include:

  • RF Transceiver — Lime Microsystems LMS7002M
  • FPGA — Altera MAX 10:
    • 169-pin FBGA package
    • 16K Les
    • 549KB M9K memory
    • 2,368KB user flash memory
    • 4x fractional phase locked loops (PLLs)
    • 45x 18×18-bit multipliers
    • 130x general purpose input/output (GPIO)
    • Single supply voltage
    • Flash feature
    • FPGA configuration via JTAG
  • Memory:
    • EEPROM memory — 256KB for RF transceiver MCU firmware/data
    • Flash memory — 4MB flash memory for data
  • Interfaces:
    • 8x FPGA GPIO pin-header (3.3 V)
    • USB 3.0 Type-A
    • Coaxial RF (SMA) connectors
    • FPGA GPIO and JTAG connectors
  • Other features:
    • Clock system — 30.72 MHz onboard VCTCXO; VCTCXO tunable via onboard DAC
    • LEDs — 2x dual-color (red/green)
  • Dimensions: 69 mm x 31.4 mm
  • Operating system support — Snappy Ubuntu Core (Linux), running on USB-connected host system

 
Further information

The LimeSDR Mini board’s Crowd Supply campaign is currently 65 percent funded. The board is available starting at $139, with options including a $40 case and a $40 antenna set (both are shown above). Shipments, which are free to the U.S. or $10 elsewhere, are expected to begin by the end of this year. More information may be found in the LimeSDR Mini Crowd Supply page.
 

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