Integrated Phased Array Systems in Silicon Presented by Srikrishna Seshan, and Omar Vicencio

Agenda Introduction Integrated Phased Arrays System Architecture Circuits Implementation Performance Applications Future

Introduction G. Moore, 1965: “Even in the microwave area, structures included in the definition of integrated electronics will become increasingly important… The successful realization of such items as phased array antennas, for example, using a multiplicity of integrated microwave power sources, could completely revolutionize radar”. The functions of a radar system were shrunk into a tiny silicon chip and small integrated antennas.

Introduction: Technology Succesful implementation of an entire microwave system in silicon at 24 GHz SiGe based eight element phased array receiver 0.18 CMOS four element phased array transmitter Used for: High speed directional communications Ranging and sensing applications (radar) The subject of the article, we are going to talk about is the succesful implementacion of an entire microwave system in silicon at 24 GHz. The microwave system in silicon includes: A fully integrated 24 GHz eight element phased array receiver in 0.18 μm silicon-germanium And a fully integrated 24 GHz four element phased array transmitter with integrated power amplifiers in 0.18 μm CMOS This can be used for high speed directional communications and ranging and sensing applications, radar.

Introduction: Silicon The Silicon offers a new set of possibilities and challenges for RF, microwave, and millimeter-wave applications, Compared to other technologies is cheaper And takes advantage of the growth of CMOS technology driven by digital circuits And the integration leads to a system-on-a-chip solution: smaller size Lower cost compared to other technologies. Takes advantage of the rapid growth of CMOS technology driven by digital circuits. Integration leads to a system-on-a-chip solution: smaller size.

Why 24GHz? Why do they use the 24 GHz frequency? Because in Higher frequencies there are more bandwidth while reducing antenna size and spacing. The Industrial Scientific and Medical band from 24 to 24.25 is used for wireless point top point communcations The Federal Communications Commission opened the 22-29GHz band for vehicular radar systems (Ultra Wide Band –UWB)

Phased Arrays Multiple antenna system, can form beams and nulls in desired directions by controlling the time delay and gain of the signal in each path independently. Phased array, historically employed in radar and radio astronomy applications, is a class of multiple antenna systems. It can form beams and nulls in desired directions by controlling the time delay and gain of the signal in each path independently. The array gain and spatial directivity achieved in a phased array system provide a logarithmic increase in channel capacity with an increase in the number of elements in the phased array due to the logarithmic dependence of channel capacity on signal-to-noise ratio (SNR)

Phased Arrays: Advantages Phased array provides a directional communication channel. Reduction of interference, and better sensitivity capabilities at the receiver. Improvement of SNR, increasing channel capacity. The antenna size and the spacing between the elements are inversely proportional to the frequency: Larger bandwidths are available at higher frequencies. In high speed wireless communications, the limiting factors are the multipath fading and the co-channel interference. Multiple spaced antennas form statistically independent communications channels in a fading environment, and phased array provides a directional communication channel. The phased array antennas can be made insensitive to unwanted signals, limiting interference, the power from a undesired direction can be reduced. The reduction of interference, improves the SNR signal to noise ratio, and this increases the channel capacity. The antenna size and the spacing between the elements are inversely proportional to the frequency. This inspires a move to higher frequencies to leverage spatial processing techniques, as multiple antenna systems can be made physically smaller. In addition, larger bandwidths are available at higher frequencies. Small-sized highly integrated low-power multiple-antenna systems can also be used for ranging and sensing applications such as radar.

System Architecture Phased array transmitter or receiver: several signal paths each connected to a separated antenna, arranged in different spatial configurations. For a given power level at the receiver, the power that has to be generated is lower For a transmitter with m elements, radiating each P Watts, the total power is m2P watts in the receivers desired direction (m2 comes from the coherent addition of the electromagnetic fields) The directivity of the transmit-receiver pairs can result in higher frequency reuse ratios. Multiple antenna phased arrays can be used to imitate a directional antenna whose bearing can be controlled electronically. This electronic steering makes it possible to emulate antenna properties such as gain and directionality, while eliminating the need for continuous mechanical reorientation or the actual antenna. A phased array transmitter or receiver consists of several signal paths each connected to a separate antenna. The antenna elements of the array can be arranged in different spatial configurations. The array can be formed in one, two, or even three dimensions, with one or two dimensional arrays.

System Architecture: Principle of Operation Receiver The radiated signal arrives at different times at each of the spatially separated antennas. The difference in time of arrival depends upon the angle of incidence and spacing between the antennas. An ideal phased array receiver compensates for the time delay difference between signals coherently to enhance the reception from the desired direction while rejecting emission from other directions Receiver is capable of nulling out interferers as long as they do not originate from the same direction as the signal

System Architecture: Principle of Operation Transmitter The signals in different elements are delayed by different amounts so that the signals add up coherently only in the desired direction. Incoherent addition of the signal in other directions results in lower radiated power in those directions Transmitter generates less interference at receivers that are not targered

Circuit Implementation: Receiver LNA Low noise factor, Well defined real input impedance, Adequate gain to compensate for mixer noise Low power design SiGe HBT with cutoff frequency of 120 GHz Power output 50 W Mixer and IF Combining Network Input of mixer stages matched to output of LNA Gilbert-type mixers are used to downconvert the 24 GHz RF signal to a 4.8 GHz IF signal IF Amplifier and Mixer Interference in this section is minimum thereby relaxing design requirements Receiver 1) LNA: The LNA is the most critical block in the receive chain in terms of sensitivity. It needs to have a low noise factor, a well-defined real input impedance (typically 50 W), and sufficient gain to suppress the noise of the subsequent mixer. The LNA used in a phased array system requires a particularly low power design. Recent advances in the silicon CMOS and SiGe BiCMOS processes have extended the operation range of silicon-based integrated LNAs from low gigahertz range to much higher frequency bands. The process used in this work provides SiGe HBT with cutoff frequency of 120 GHz. The LNA is designed to be well matched to 50W (S11 less than -10 dB). 2) Mixer and IF Combining Network: Gilbert-type double-balanced multipliers are used to downconvert the single-ended 24GHz RF signal to a differential signal at 4.8GHz. 3) IF Amplifier and Mixer: The IF amplifier is the first circuit block after signal combining. The IF amplifier and mixer consume 1.6 and 2.3 mA of dc current, respectively.

Circuit Implementation: Trasmitter IF and RF Upconversion Mixers Gilbert-type upconversion mixers using 0.18 um CMOS transistors. Tunable passive loads Cascade of tuned stages in the RF path of each element Switchable capacitors controlled by programmable shift registers. PA Cacaded 2 stage PA PA designed to be single ended Transmitter IF and RF Upconversion Mixers: The base-band to 4.8GHz mixers common to all elements and the 4.8GHz to 24GHz upconversion mixers in each element are Gilbert-type upconversion mixers using 0.18mm CMOS transistors. The first upconversion mixer consumes 3.8 mA of the current while the buffers following this consume 4.3 mA. Tunable Passive Loads at 24 GHz: There are a cascade of tuned stages in the RF path in each element. This exacerbates any off-tuning in the passive loads. To avoid the problem of gain loss due to off-tuning, switchable capacitors, controlled by programmable shift registers, were implemented at the output of some of the high-frequency stages. PA: All the circuits up to and including the 24 GHz PA driver are differential while the PA was designed to be single ended. To avoid power and efficiency loss in PA, a balanced-unbalanced converter (balun) was placed before the PA. This eliminates the need for an off-chip balun or a differential antenna. The balun was realized with a single-turn transformer to minimize substrate loss through capacitive coupling. The CMOS PA, consists of two gain stages. Each gain stage is composed of a cascode transistor pair to ensure stability and increase breakdown voltage.

Circuit Implementation: LO Path Circuitry Similar on transmitter and receiver chips. 16-phase VCO with a center frequency of 19 GHz is used VCO designed as a ring of eight differential CMOS amplifiers with tuned loads. The 16 phases generated by the VCO are distributed to the phase selectors in each element The LO path circuits are similar on transmitter and receiver chips. In both chips, a 16-phase VCO with a center frequency of 19 GHz is used to generate the LO. The VCO is designed as a ring of eight differential CMOS amplifiers with tuned loads.

Circuit implementation: Tx

Circuit implementation: Rx

Performance Transmitter Receiver Image signal attenuation 24 dB Overall image singal rejection of 43 dB Isolation 35 dB Output power measured PA 14.5 dBm Receiver Gain of single element 43 dB at 23 GHz Overall Noise figure 7.5 dB over 250 MHz Improvement in output power due to array function 18 dB Improvement in Noise power is 9 dB The phased array system is implemented in IBM 7HP SiGe BiCMOS technology with a bipolar of 120 GHz and 0.18 mm CMOS transistors with an of 65 GHz. It offers five metal layers with a 4 mm-thick top analog metal used for on-chip spiral inductors as well as for transmission lines routing the high-frequency signals. The size of the receiver chip is 3.3 mm X 3.5 mm while the transmitter chip occupies 6.8 mm X 2.1 mm of die area. LO Path Performance Receiver Performance Transmitter Performance

Applications Short range radar systems Radio astronomy Motion sensors Wireless communications Military applications Vehicular Radar systems The high-frequency beams that the system generates and receives may one day handle many functions, including the usual radar jobs of ranging and location. In cars, for example, the chip might be used to detect other vehicles looming in the fog. The chip may also be used for wireless communications, since it has a broad bandwidth or range of frequencies at which it communicates. And it produces a bit stream at roughly the rate of fiber optics, more than enough for quick downloads of movies and other digital data. ''D.S.L. can go to several hundred kilobits, and fiber can go to several gigabits per second,'' Dr. Hajimiri said. The radar chip can achieve bit rates up to a gigabit per second, partly because of the concentrated nature of the beam, he said. ''The beam created by the chip is highly focused,'' he said. The chip could combine the functions of sensing and communication, say, for a group of army tanks that needs to stay in touch in the field. ''Using these extremely high frequencies, you can first capture location, sending out pulses and scanning the area like a bat,'' said Volkan Ozguz, chief scientist at Irvine Sensors in Costa Mesa, Calif. Irvine Sensors makes miniature electronic systems, including sensors. ''Then, using the same chipset, you can start communicating at high frequency,'' exchanging information without switching to different equipment, he said.

Future Gigabit wireless LAN’s Automotive radar applications High data rates without increase in available bandwidth Automotive radar applications Assisted parking Blind spot detection

References A. Hamiri, H. Hashemi, A. Natarajan, X. Guan,“Integrated Phased Array Systems in Silicon”, Proceedings of the IEEE, vol. 93. no. 9, pp. 1637-1655, Sept. 2005. X. Guan, H. Hashemi, and A. Hajimiri, “A fully integrated 24-GHz eight-element phased-array receiver in silicon”, IEEE J. Solid-State Circuits, vol. 39, no.12, pp. 2311-2320, Dec. 2004. A. Natarajan, A. Komijani, and A. Hajimiri, “A 24 GHz phased-array transmitter in 0.18 um CMOS”, in ISSCC Dig. Tech. Papers, vol. 48, 2005, pp. 212-213.