Proceedings of the 11th European Radar Conference
122 GHz Single-Chip Dual-Channel SMD Radar Sensor with Integrated Antennas for Distance and Angle Measurements Mekdes Gebresilassie Girma∗ , Juergen Hasch∗ , Markus Gonser∗ , Yaoming Sun† , and Thomas Zwick‡
∗ Robert
Bosch GmbH, Corporate Sector Research and Advance Engineering, P.O. Box 10 60 50, D-70049 Stuttgart, Germany † HK Microsystem Integration Ltd., Hong Kong ‡ Institut f¨ ur Hochfrequenztechnik und Elektronik, Karlsruhe Institute of Technology (KIT) Kaiserstr. 12, 76128 Karlsruhe, Germany Email:
[email protected]
Abstract—This paper presents a single-chip, dual-channel Surface-Mounted-Device (SMD) radar sensor with two integrated on-chip antennas operating at D-band. The design comprises of a fully integrated transceiver circuit with quasi-monostatic architecture and a 60 GHz push-push voltage-controlled-oscillator (VCO) that operates between 114 GHz and 124 GHz. All analog building blocks have digital-control interfaces and are controlled via a serial-peripheral-interface (SPI) to reduce the number of bond-pads and facilitate the communication between digital processor and analogue building blocks. The two electromagnetically coupled patch antennas are placed on the top of the die with 9-dBi gain and have a simulated efficiency of 60%. The chip consumes 450 mW and is wire-bonded in an open-lid 5 mm × 5 mm quadflat no-leads(QFN) package. Appropriate signal processing for the estimation of range, and azimuth angle in multiple object situation is presented. Index Terms—Millimeter wave integrated circuits, 122 GHz transceiver, SiGe-BiCMOS, D-band, On-chip Antenna, FMCW, DoA, Mono pulse, D-band
noise amplifiers (LNAs), and sub-harmonic mixers (SHMs). The chip is implemented in 130 nm SiGe-BiCMOS process with fT /fmax = 280/300 GHz and dissipates 450 mW. II. M ONOPULSE F UNCTIONAL P RINCIPLE Multichannel reception can be used for direction of arrival (DoA) finding. Therefore, the principle of monopulse phase direction finding lies in the reception of signals reflected from a target simultaneously along several independent receiving channels with the subsequent comparison of their parameters. Figure 1 shows a schematic representation of angle measure-
I. M OTIVATION Due to the tremendous progress in BiCMOS and CMOS silicon technologies, millimeter-wave (30 GHz- 300 GHz) applications become achievable and affordable for mass-production, and therefore a higher market penetration in consumer electronics. Compact, low- power and low cost sensors are the key parameters with promising industrial and consumer applications. Signal frequencies at D-band are very attractive due to their high spatial resolution, the resulting compact chip size, and small antenna dimension. In addition to a contactless distance and speed sensing, determining the direction to a target is one of the basic tasks of a radar. A minimum of two receiving channels are required to obtain information about the direction of signal reflection. Several 122 GHz radar sensors have been demonstrated to date, [1], [2], [3], while effective, they can only measure distance or velocity, and cannot track a target angle. To address this issue, a dual channel single chip SiGeBiCMOS transceiver integrating two on-chip antennas for angular measurement was developed. The monolithically integrated radar includes a VCO, power amplifiers (PAs), low-
978-2-87487-037-8 © 2014 EuMA
Fig. 1. Principle of angular measurement based on phase difference in the azimuth plane
ment principle with two parallel RX channels. Assume two antenna separated by a distance d, with a wavefront incident angle θ, then the extra path the signal must travel between RX1 and RX2 results in a phase difference, ΔΦ, between the two antennas. This can be used to calculate the direction of arrival using: λΔΦ θ = asin (1) 2πd Due to the azimuth position of the target, a linear phase shift can be observed in the receive signal between the consecutive antennas. These phase shifts can be exploited in order to obtain the corresponding frequency and hence the DoA. Due
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to the distance d = λ2 between the two antenna elements and according to the spatial sampling theorem, azimuth angles in the range of ϕ = − π2 , π2 can be measured in an unambiguous way. For unambiguous results, the antennas should be spaced half a wavelength apart, or less. III. T RANSCEIVER A RCHITECTURE The block diagram of the proposed transceiver is illustrated in Figure 2. The transmitter is driven by a 60 GHz LO signal generated by a push-push oscillator to further reduce the VCO fundamental to around 30 GHz. A divide-by-16 chain, at approximately 3.8 GHz, is provided to an off-chip phase-locked loop (PLL), in order to lock the VCO to a stable reference frequency and modulate the transmit signal in frequency-modulated continuous-wave (FMCW) mode. Each of the two identical transmit channels include, a frequency doubler, a coupler and bi-directional power detector (PD) to measure the absolute output-power and antenna matching. This configuration allows to fully characterize the transmitter path up to the antenna by using DC measurements. Two antennas are integrated to transmit and receive a signal simultaneously, thus illuminating the target from different directions. In the receiver chain, the Low-Noise-Amplifiers (LNAs) are followed by two sub-harmonically pumped mixers (SHM), to mix the receive and LO signal to baseband. The two passive SHMs are driven by the same 60 GHz LO signal as the input of the frequency doubler. The baseband signals are further amplified by a pair of variable-gain amplifiers (VGA) before they reach the external analog-to-digital converter (ADC). All building blocks can be controlled digitally via SPI.
A. On-chip Antenna concept Figure 3 presents the layout of the 122 GHz electromagnetically coupled on-chip microstrip antennas. The proposed antenna configuration consists of a parasitic resonator placed on top of the radio chip excited by a shorted patch antenna implemented in the back-end layer stack, a similar approach as in [1]. In addition to the global ground plane the 3- bottom metal layers (M1 -M3) are shunted together and they acts as the ground plane for the antenna, and it isolates the antenna from the lossy silicon substrate. The quarter wavelength patch is located at the top-metal layer (TM). The simulated directivity for two antenna elements is D ≈ 9.2 dBi and the simulated gain is G = 8.6 dBi ±0.7 dB at 120 - 123 GHz (G=D, efficiency = 60±8%). The spacing between the two antennas is 0.5λ at 122 GHz. The mutual coupling between the antennas is simulated using the 3-D electromagnetic simulator, CST, and is
