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The 700 to 2600 MHz frequency band will be used by ever more mobile devices (up to 50 billion by the end of the decade according to forecasts), as it will remain the sweet spot in the frequency spectrum for wide area coverage macro cells due to the optimal propagation loss in the light of frequency reuse. The capacity of the cellular networks has to be increased through:

• An increase in the number of cells, albeit at the expense of rising infrastructure deployment cost and power consumption
• An increase in the used spectrum per cell - i.e. the number of frequency bands per base transceiver station (As of 4G, there are 41 and counting frequency bands licensed in the 400 MHz to 3.8 GHz band.). This technique however requires multi-band support at the smartphone side as well.

In addition, solutions are necessary to increase the ACLR and the efficiency of the transmitter, and to reduce the EVM of the receiver and the overall footprint of the antenna, front-end module and transceiver. Indeed, without a reduction in ACLR, the network will become unreliable as more mobile connections will be interrupted or dropped, due to increasing interference. In addition, the inter-band CA and the MIMO technique, which are touted to improve the data rate, will require more complex front-end modules. The MIMO technique in particular requires multiple antennas, front-end modules and transceivers per mobile device, and therefore also a smaller footprint per antenna, front-end module and transceiver, as well as improved efficiency, in order to maintain the current battery autonomy and to prevent sleek mobile device designs from becoming overheated.

State-of-the-art duplexers and power amplifiers, and to a lesser extent antennas, are frequency band-specific components - i.e. they are neither ultra-wideband nor frequency-tunable. Given the ever-increasing number of cellular communication frequency bands to be supported and hence the higher part count, it should be clear that a tunable approach reduces BOM cost...

Tunable Antenna

The design of antennas for mobile devices is becoming increasingly challenging. New wireless standards, touting enhanced throughput, require both the coverage of more frequency bands per antenna (to support LTE-A inter-band carrier aggregation for example), as well as more antennas per mobile device (to support IEEE802.11ac or LTE-A MIMO for example). At the same time, mobile devices become sleeker. The Chu-Harrington limit, however, bounds and relates the bandwidth, the efficiency and the volume of electrically small antennas. ChipDesign has therefore developed a multi-functional tunable antenna, which allows multi-band 2G/3G/4G cellular communication, 866 MHz RFID tag reading, L-band DVB-H and S-band SDARS broadcast reception, L2 GPS navigation and 2.45 GHz WLAN (IEEE802.11a/b/g/n/ac) and WPAN (Bluetooth and ZigBee) connectivity. ChipDesign believes that its on-demand-reconfigurable multi-functional antenna paradigm can provide a solution to the spectrum shortage and the MIMO-on-the-handset conundrum and enable the next leap in download capacity for mobile devices.

ChipDesign's tunable antenna for mobile devices consists of a low-profile electronically-tunable electrically-small (18.5 cm long) slot antenna, which allows for improved receiver selectivity^1,2.

• Band coverage:
  • Well-matched (dB20(|S₁₁|) < -10 dB, VSWR < 1.9) frequency bands are the 700 MHz, 866 MHz (ISM), 900 MHz, 1227 MHz (GPS L2), 1800 MHz, 1900 MHz, and 2100 MHz band. For the cellular bands, the full TX band, the duplex gap, and the full RX band are covered, allowing contiguous and non-contiguous intra-band CA with an instantaneous bandwidth up to 100 MHz, if applicable.
  • Poorly-matched (dB20(|S₁₁|) < -6 dB, VSWR < 3) frequency bands are the 433 MHz (ISM) and 450 MHz band for the Seeed version, and the 2.45 GHz (ISM) and 2.6 GHz band for the OEM version.
• Directivity: The full-space radiating version is recommended for IoT devices and tablets, whereas half-space radiating version, currently under development, is recommended for smartphones in order to meet the SAR specification. A λ₀/2 full-space radiator has a directivity of 1.6 dBi, whereas λ₀/2 half-space radiator has a directivity of 10log₁₀(π) ≈ 5 dBi.
• Efficiency: TBD. The bandwidth and efficiency of electrically-small antennas with sufficient instantaneous bandwidth are bounded by the Chu-Harrington limit.
• Programming: The frequency band can be programmed using three PWM outputs of Arduino micro-controller boards, such as the Arduino Uno or the Seeeduino Lotus, or 5 V Arduino shield compatible mbed³ micro-controller boards, such as the u-blox C027.
• Tunable elements: 3 RF varactor diodes integrated in the radiating aperture for improved antenna match tuning. The tuning time is limited by the RC constant of the low pass filter on the PWM outputs. The RF varactor diodes do generate spurious emission.

OEM version: 700 MHz - 2.6 GHz - Test hardware influencing the antenna match: 5 V Seeeduino Lotus micro-controller board and 10 cm U.FL to SMA adapter.

Freq. [MHz]	Application	dB20(|S11|)	VSWR	leftValue	topValue	rightValue
700	Cellular	-18	1.27	123	2	255
866	ISM	-23	1.14	114	27	0
900	Cellular	-30	1.05	125	1	34
1227	GPS L2	-18	1.28	96	1	253
1452-1492	DVB-H	-11/-4.9	1.8/3.5	255/1	255/1	255/1
1575.42	GPS L1	-6.6	2.75	2	0	2
1800	Cellular	-14	1.5	163	1	2
1900	Cellular	-31	1.05	141	1	18
2100	Cellular	-16.5	1.35	181	1	91
2320-2345	SDARS	-7.6	2.42	20/74	192/253	14/13
2450	ISM	-7.1	2.5	162	1	2
2600	Cellular	-9.2	2.05	0	2	216
See presentation

Seeed version: 433 MHz - 2.1 GHz - Test hardware influencing the antenna match: 5 V Seeeduino Lotus micro-controller board and 10 cm U.FL to SMA adapter.

Freq. [MHz]	Application	dB20(|S11|)	VSWR	leftValue	topValue	rightValue
433	ISM	-8.2	2.26	147	0	255
450	Cellular	-7.8	2.35	142	0	255
700	Cellular	-20	1.2	255	23	255
866	ISM	-20	1.2	33	254	94
900	Cellular	-22.7	1.2	33	254	111
1227	GPS L2	-25	1.12	112	135	201
1452-1492	DVB-H	-11.5/-6.6	1.72/2.7	254/254	254/254	254/254
1575	GPS L1	-5.5	3.2	1	0	1
1800	Cellular	-9.8	1.9	121	1	0
1900	Cellular	-13.7	1.5	144	0	50
2100	Cellular	-31	1.05	101	22	44
2320-2345	SDARS	-12.3/-10.8	1.6/1.8	1/1	82/89	0/255
2450	ISM	-4.7	3.7	22	133	141
2600	Cellular	-2.9	5.8	0	0	0

The unique selling proposition of ChipDesign's tunable antenna:

• The OEM version of this tunable antenna is an on-demand reconfigurable multifunctional antenna, supporting 2G/3G/4G cellular communications, 866 MHz RFID tag reading, DVB-H (L-band) and SDARS (S-band) broadcast reception, GPS (L1/L2) navigation, and 2.45 GHz WLAN/WPAN (Bluetooth, ZigBee) connectivity.
• It raises the bar in
  • Cost:
    • Part count reduction to 3 identical tunable antennas per mobile device to allow for concurrent cellular communication, GPS navigation, as well as WLAN/WPAN connectivity. The use of identical antennas implies a single SKU.
    • It enables the use of low cost FR4 substrate through the electronic compensation of its dielectric constant and thickness variations.
    • Product development cycle time reduction through the electronic compensation of the battery, case and screen coupling effects.
  • Performance:
    • A single feed reduces the antenna switch module (ASM) complexity.
    • A single tunable antenna can be made larger than the antennas of a multi-antenna cellular antenna solution and will therefore have a larger bandwidth and/or higher efficiency, as the Chu-Harrington limit upper-bounds the bandwidth and the efficiency specifications by the volume specification. Higher efficiency allows lower EVM and an increase in data rate.
• It furthermore enables:
  • A further increase in data rate through inter-band CA and MIMO (A second tunable antenna can be reconfigured on-demand as either a second cellular antenna for inter-band CA or a cellular/WLAN diversity antenna for MIMO),
  • Cognitive radio solutions to frequency band-specific mobile network congestion.

Price:

• 100 EURO for the OEM version (Order now or request a quote for a non-exclusive license fee).
• 25 EURO for the Seeed version (Order now).

Tunable Front End IC

ChipDesign's tunable front end IC architecture for cellular devices is centered around a novel envelope tracking CMOS power amplifier design, featuring integrated tunable duplex filtering. CMOS power amplifier design for cellular front end modules is challenging, because of the stringent requirements for the adjacent channel leakage ratio (ACLR), the bandwidth, the out-of-band noise in the RX band, the power added efficiency (PAE) and the output power.

New capacity-increasing LTE-A techniques, such as inter-band CA and MIMO will further constrain the footprint and the power dissipation of the power amplifier. ChipDesign therefore proposes to implement PA power combining, as well as highly-selective duplex filtering, in the acoustic energy domain, using integrated tunable piezoelectric transducers (see BE patent application 20140066). PA power combining in the acoustic energy domain allows for a footprint and loss reduction⁴, because reactive components implemented in the acoustic energy domain are smaller and have higher Q factors. In addition, tunable filter stages can be added to suppress noise and spurs, most notably in the RX band. The tunability of the duplex filter stages will furthermore reduce the BOM, as well as the complexity of the antenna switch module, which is to be inserted between the duplexer and the antenna matching tuner.

Contact us for the Verilog IP cores of the digital building blocks and the Verilog-A models for the RF building blocks.

IoT Development Board

The term internet of things (IoT) initially referred to networks of RFID tagged objects in order to ease identification and tracking of these objects. Over the years, though, the meaning of the term has evolved to include countless devices connected wirelessly to the internet. These connections can be sensor-to-machine, machine-to-people (M2P), or machine-to-machine (M2M).

Preliminary specifications:

• Cloud access:
  • USB 2.0 device/host/OTG controller
  • 10/100 Mbps Ethernet controller
  • Quad-band (850/900/1800/1900 MHz) GSM/GPRS module with integrated ChipDesign tunable antenna:
    • AT command support
    • SMS messaging support
    • TCP/UDP and HTTP protocol support
    • Optional: voice call support (An external speaker and microphone circuit is needed.)
• Power supply options:
  • Battery (4.5-9 V)
  • PoE:
    • IEEE802.3af compliant
    • 36-57 V input voltage range
    • 9 V output
    • 1500 V isolation (input to output)
    • High efficiency DC/DC converter: typically 75% @ 50% load
    • Low output ripple and noise (100 mVpp)
    • Overload and short-circuit protection
  • Solar panel
  • USB charger (5V)
• Programming: mbed
• Sensor & actuator support:
  • 96 MHz ARM Cortex-M3 microcontroller with 32 kb of SRAM and 512 kb of flash
  • Serial peripherals besides ethernet and USB:
    • 3 x UART with fractional baud rate generation, RS-48, modem control, and IrDA
    • CAN 2.0 controller
    • 2 x SPI controllers
    • 2 x I²C-bus interfaces with one supporting fast mode plus (1-Mbps data rates)
  • Analog peripherals:
    • 6 x 12-bit ADC
    • 6 x PWM
    • 10-bit DAC
  • Other peripherals:
    • Ultra-low-power (< 1 μA) RTC
    • General-purpose DMA controller with eight channels
    • Up to 10 x GPIO
    • PWM motor control support for single-phase motors and quadrature encoder interface support for three-phase motors
    • 4 32-bit timers/counters
• Size:
  • Breadboard fitting prototyping form-factor
  • 40-pin 0.1 inch pitch DIP package, 100 x 35 mm

Footnotes

^{1. The tunable antenna can be used in conjunction with software defined radios (SDRs) such as for example the Ettus/NI USRP, the FlexRadio, the FUNcube Dongle, the HackRF and the RTL-SDR.↩}

^{2. UWB antennas, such as the log-periodic and the Archimedean spiral antenna, are electrically-large and therefore do not allow for MIMO on the handset, and offer no selectivity.↩}

^{3. 3.3 V mbed micro-controller boards will require 3.3 V to 5 V level shifters to be inserted to bias the varactors up to 5 V and cover the entire tunable frequency range of the tunable antenna.↩}

^{4. Efficiency-enhancing techniques such active load modulation (outphasing and Doherty) or supply modulation (envelope tracking and envelope elimination and restauration) could be used. The implementation of these efficiency-enhancing techniques itself however is also based on power combiners and dividers.↩}