60 GHz T/R Module Enables Short-Range Multi-Gigabit Communications
A number of wireless multimedia distribution applications under consideration for development include high-definition multimedia interface (HDMI) cable replacement/uncompressed high-definition (HD) video streaming, mobile distributed computing, wireless docking stations, wireless gigabit Ethernet, fast bulky file transfer and wireless gaming. Additionally, some are looking to install a larger number of WPAN clients in an in-building environment without cross-talk amongst other users or other WLAN/LAN electronics. These broadband applications call for a significant increase in the capacity of wireless networks, far in excess of what can be accommodated in RF frequency bands.
For several years, the 60 GHz region of the electromagnetic spectrum has received considerable interest due to benefits such as the availability of wide unlicensed bandwidth (up to 7 GHz in the US), the range-limited propagation characteristics (higher path loss and oxygen absorption of 15 dB/km) that allow high-density short-range links, and because of the short wavelength that allows very compact antenna structures. Hence, the 60 GHz spectrum provides the necessary bandwidth and inherent interference mitigation to provide multi-gigabit short-range communications (radial range of 10 meters or less).
One exciting application is WirelessHD™ aka WiHD™, which will serve as the first and only wireless digital interface to combine uncompressed high-definition video, multi-channel audio, intelligent format and control data, and Hollywood approved content protection. For end-users, elimination of cables for audio and video will dramatically simplify home theater system installation and eliminate the need to locate source devices in the proximity of the display. The technology will also support the development of adapter solutions that will be capable of supporting legacy systems.
The WiHD specification has been architected and optimized for wireless display connectivity, achieving in its first generation implementation of high-speed data rates up to 4 Gbps at ten meters for the CE, PC and portable device segments. Its core technology promotes theoretical data rates as high as 25 Gbps, permitting it to scale to higher resolutions, color depth and range. The 60 GHz band has the spectral availability to achieve multi-gigabit data rates necessary to reliably distribute high quality, high-definition uncompressed video. In addition, the 60 GHz band has high allowable transmit power to achieve these high data rates at distance.
A key to bringing 60 GHz-based products to the market place will be the availability of reasonably priced, repeatable, mass producible transceiver electronics. Numerous challenges exist for 60 GHz transceiver design, including the limited amplifier gain, reduced power output capabilities for transistors, amplification of frequency instability (phase noise) and the proliferation of parasitics that essentially forces designers to take an MMIC/RFIC approach.
One of the first commercially available transmit/receive modules to overcome these challenges was announced by Endwave Corp. in June at this year’s IMS show in Atlanta, GA. The high-performance and reliable T/R module seamlessly integrates transmit, receive and LO functions together into the overall system architecture.
Packaging a transmitter and receiver together without “crosstalk” or performance degradation is a challenge, especially at V-band (60 GHz). The engineers introduced a measure of frequency-plan versatility to help users avoid system spurious nightmares. Attention was also paid to group delay caused by VSWR induced pass-band ripple and out-of-band filter skirts as well as suppression of local oscillator (LO) leakage that might otherwise adversely affect transmitter linearity.
The transceiver design, shown in Figure 1, is based on a direct-conversion architecture that utilizes independent Tx and Rx local oscillators and versatile programmable phase lock loops. A reference frequency can be supplied externally at any of a number of different frequencies up to 100 MHz.
The T/R module contains a direct-conversion receiver, where the received radio frequency signal is amplified by a low noise amplifier (LNA) and directly down-converted to a baseband signal via a mixer with a LO provided by a frequency doubler driven by a PLL-controlled voltage-controlled oscillator (VCO). The PLL provides a frequency regulating system that prevents frequency shift due to temperature changes and other influences. The doubler allows the VCO to be designed at half the LO frequency, easing the VCO design itself while reducing the injection pulling from RF signals conducted or radiated from the LNA. Typical receiver specifications at 60 GHz are a noise figure of 5 dB and a gain of 14 dB.
The transmit chain is also based on a direct-conversion architecture with a similar PLL-controlled VCO, doubler and up-converter mixer driving a pair of cascaded driver and power amplifiers. The transmitter output power measured at P1dB compression exceeds +5 dBm with ±1.0 dB flatness over any 2 GHz operating bandwidth. Balance between I and Q ports measures better than 1.5 dB in amplitude and 10 degrees in phase over a 10 MHz (DC) to 1 GHz baseband frequency range.
To overcome the difficulties normally associated with direct-conversion or zero-IF architectures, Endwave’s modules provide a bias line for each of the I and Q mixers. The user can adjust the voltages on these lines to completely null out the carrier on the transmitter and to zero the DC output of the receiver. Alternatively, they can be adjusted to reject images.
Versatility was a primary focus during the design of the modules. Though most users will prefer the direct-conversion mode, the design will also allow IF signals to be fed to the transmitter and exit from the receiver with IF frequencies up to 1 GHz. In addition, it is possible to adjust the transmitter and receiver frequencies to coincide to create a high sensitivity radar.
Units measure only 9 cm (3 ½ in) in length and are available with built-in patch antenna arrays or with waveguide inputs and outputs. With 60 degree half-power beamwidths, the built-in antennas create a broad pattern suitable for unaligned links. If desired, the user can add lenses or reflectors (at low cost) to achieve narrower beamwidths and longer ranges. Of course, the units with waveguide ports allow the user to attach antennas with an even broader range of radiation patterns.
Among other things, the 60 GHz community is looking to facilitate technical advancement in a wireless high-definition digital interface in order to simplify high-definition A/V transmission and high-definition content portability for consumers. With the proliferation of digital devices in the home, along with the increasing availability of higher resolution high-definition content, consumers are seeking flexible ways to transfer content among these devices, playing it back and taking it with them. The Endwave 60 GHz T/R module is one of the new and exciting millimeter-wave enablers to this movement.
RS No. 306