Project C04 - Silicon Integrated Transceiver Components for Multi-Color
Imaging and Mobile CW Spectroscopy

Principal Investigator: Prof. Dr. Ullrich Pfeiffer

Achieved results and methods

The 1^st phase of C04 addressed the fundamental bandwidth, output power, and sensitivity limitations of integrated continuous-wave transmitters and receivers, resolving various issues related to the second research sub-question (Circuits). Fig. 1 summarizes the progress of C04. The central aim of the first two phases was to extend the multi-color concept toward gapless spectral coverage of a whole decade of bandwidth with a dynamic range larger than 50 dB (0.15-1.5 THz). Achieving this aim required substantial progress in sub-harmonic THz front-end design, circuit-antenna cointegration, and the design of broadband on-chip frequency multiplier-chains. Table 1 highlights the breakthroughs achieved in these fields within C04 and compares them to the state of the art prior to MARIE. By using novel methods for efficient harmonic signal generation, we achieved world records and a five times improvement of the output power for silicon-integrated THz sources around 430 GHz [3]. Moreover, we have increased the bandwidth of on-chip frequency multiplier chains by a factor of two, while at the same time increasing the maximum output power by a factor of ten around 300 GHz. Although we expect further progress regarding circuit design methods and device technology to be necessary for realizing remote spectroscopy in the whole THz band, the herein-achieved component-level advances enabled us to build bistatic silicon-based THz spectroscopy systems for the frequency range between 0.15-1.5 THz. Addressing the first research sub-question (Multi-color spectroscopy systems), we will present an integrated multi-color spectrometer chipset continuously covering this frequency range with a (simulated) dynamic range larger than 75 dB which is currently under characterization.

* will be published soon

Table 1: Comparison table highlighting the advances of C04 regarding integrated multiplier chains and harmonic THz sources as compared to the state of the art preliminary to MARIE.

A leap in on-chip driving circuit bandwidth is necessary to enable gapless spectral coverage with the multi-color approach, which motivated our research in novel multiplier-chain architectures in C04. We achieved a record 3-dB bandwidth for on-chip multiplier-chains by exploiting broadband optimization of phase relations between the transconductance pair and  the switching squad in three cascaded Gilbert-cell doublers [2]. The measured 3-dB bandwidth spans between 210-290 GHz (32%), and the measured output power is -7.7 dBm. During the 1^st phase we identified that complex parasitic harmonic content of conventional on-chip multiplier chains may severely impair multi-color spectrometers  due to resulting intermodulation distortions. Thus, we investigated novel tripler-based multiplier-chains with dedicated harmonic filters between the multiplication stages. The filters exploit the odd and even symmetry of differential circuits for wideband all-pass filtering of parasitic harmonic content by using tightly coupled line sections. This was used for the synthesis of a new class of compact low-loss on-chip filters. An x9 multiplier chain with cascaded triplers, amplifiers [6], filters, and broadband interstage matching is fabricated and characterized in a high-speed 0.13-µm SiGe-HBT technology with f_max of 700 GHz serving as a basis or the final multi-color demonstrator [4]. Measurements show a 3-dB bandwidth spanning 244-300 GHz (28%), a peak output power of 9.6 dBm, and a spurious-free dynamic range between 25 dB and 50 dB in the entire passband [4].

Integrated multi-color spectrometer

Different system topologies were studied for the final multi-color spectrometer. Despite the advances in circuit bandwidth, a single multiplier-chain is not capable of providing gapless frequency coverage. Notably, an odd- and even-mode harmonic generator, e.g., a single-ended driven nonlinear device, would require a relative bandwidth of at least 66% for continuous spectral coverage. Thus, C04 utilized two parallel frequency multiplier paths with different multiplication factors to close the covered spectrum by harmonic interleaving in both the receiver and the transmitter. The two multiplier-chain paths feed separate harmonic generators (in the transmitter) or sub-harmonic mixers (in the receiver) (Fig. 3a)). The interleaved harmonic content is then radiated orthogonally with dual-polarized on-chip antennas. Extensive simulations have been performed to assess the projected system performance (Fig. 3b)). The simulated transmitted power per harmonic is around -25 dBm and the receiver sensitivity is better than -100 dBm/Hz up to 1.7 THz. As such, our simulations indicate that it should be technically feasible to cover the entire frequency range between 0.15-1.5 THz with a dynamic range larger than 70 dB (when referred to a 1-Hz bandwidth) without any gaps. The system is currently fabricated in a high-speed 0.13-µm SiGe-HBT technology with f_max of 650 GHz and is under characterization. Fig. 1 (in current) shows the die photo of the fabricated chip.

Monostatic architecture development

In parallel with the characterization of the transmission-based bistatic system in Fig. 3, a novel concept for designing a reflection-based monostatic system is also developed. To make the system monostatic, a duplexer is required between the transmitter and receiver which are on the same chip, the transmitted signal is reflected back by the material under test and received by the same antenna. In order for such a system to work properly there must be adequate isolation between the receiver and the transmitter such that the receiver is not blocked and desensitized by the transmitter. Moreover, such a duplexer must have harmonic behavior and low loss. Fig. 4 shows the simulation results of the proposed duplexer. The green curve shows the harmonic behavior of the TX to antenna (and antenna to RX) and the red curve shows the TX to RX leakage. As frequency increases the path loss increases inevitably, however, its harmonic behavior compensates the loss at high frequencies. In addition, although leakage is degraded as frequency increases, the generated power at higher harmonic also falls, not saturating the receiver.

Selected project-related publications

1. P. Hillger, J. Grzyb, R. Jain, U. R. Pfeiffer, “Terahertz Imaging and Sensing Applications With Silicon-Based Technologies“, IEEE Transactions on Terahertz Science and Technology, Jan. 2019 – most popular paper on IEEE Transactions on Terahertz Science and Technology for 15 months. [DOI:10.1109/TTHZ.2018.2884852]
2. T. Bücher, S. Malz, K. Aufinger and U. R. Pfeiffer, "A 210-291-GHz (8x) Frequency Multiplier Chain With Low Power Consumption in 0.13-μm SiGe," IEEE Microwave and Wireless Components Letters April 2020. [DOI: 10.1109/LMWC.2020.2979715]
3. P. Hillger, J. Grzyb, S. Malz, B. Heinemann, U. R. Pfeiffer, “A lens-integrated 430 GHz SiGe HBT source with up to -6.3 dBm radiated power”, IEEE Radio Frequency Integrated Circuits Symposium (RFIC), Honolulu, 4-6 June, 2017. [DOI:10.1109/RFIC.2017.7969042]
4. Arjith Chandra Prabhu, Janusz Grzyb, Philipp Hillger, Thomas Bücher, Holger Rücker and U. R. Pfeiffer, "A 300 GHz x9 Multiplier Chain With 9.6 dBm Output Power in 0.13-μm SiGe Technology," IEEE Radio Wireless  Week conference 2024 [DOI: 10.1109/SiRF59913.2024.10438581]
5. Arjith Chandra Prabhu, Janusz Grzyb, Philipp Hillger, Bernd Heinemann, Holger Rücker and U. R. Pfeiffer, "A W-Band Frequency Tripler With a Novel Mode-Selective Filter for High Harmonic Rejection ," 18^th European Microwave Integrated Circuit Conference (EuMIC) 2023, [DOI: 10.23919/EuMIC58042.2023.10288850]
6. Thomas Bücher, Janusz Grzyb , Philipp Hillger, Holger Rücker , Bernd Heinemann, U. R. Pfeiffer, “A Broadband 300 GHz Power Amplifier in a 130 nm SiGe BiCMOS Technology for Communication Applications ”, IEEE Journal of Solid-State Circuits, Vol.57, Issue.7, July 2022, [DOI: 10.1109/JSSC.2022.3162079]
7. K. Statnikov, J. Grzyb, B. Heinemann and U. R. Pfeiffer, "160-GHz to 1-THz Multi-Color Active Imaging With a Lens-Coupled SiGe HBT Chip-Set," IEEE Transactions on Microwave Theory and Techniques, Feb. 2015. [DOI:10.1109/TMTT.2014.2385777 ]
8. N. Sarmah, B. Heinemann and U. R. Pfeiffer, "235–275 GHz (x16) frequency multiplier chains with up to 0 dBm peak output power and low DC power consumption," 2014 IEEE Radio Frequency Integrated Circuits Symposium, Tampa, FL, 2014. [DOI:10.1109/RFIC.2014.6851691]
9. E. Öjefors, B. Heinemann and U. R. Pfeiffer, "Active 220- and 325-GHz Frequency Multiplier Chains in an SiGe HBT Technology," IEEE Transactions on Microwave Theory and Techniques, May 2011. [DOI:10.1109/TMTT.2011.2114364 ]
10. R. Jain, P. Hillger, J. Grzyb and U. R. Pfeiffer, "29.1 A 0.42THz 9.2dBm 64-Pixel Source-Array SoC with Spatial Modulation Diversity for Computational Terahertz Imaging," 2020 IEEE International Solid- State Circuits Conference - (ISSCC), San Francisco, CA, USA, 2020. [DOI:10.1109/ISSCC19947.2020.9063025]