Herbert Jaeger

A Fully Differential 77-GHz Active IQ Modulator in a Silicon-Germanium Technology

A 77-GHz IQ modulator in a fully differential circuit configuration is presented. It includes an local oscillation (LO) buffer amplifier, a medium-power output stage, a double-balanced active mixer architecture and on-chip baluns for easy characterization. A differential branch-line coupler provides quadrature phase signals at the upconversion mixer LO inputs. The circuit is manufactured in a 200-GHz transit frequency technology, and the circuit performance is shown by on-wafer measurements.

An Active Quasi-Circulator for 77 GHz Automotive FMCW Radar Systems in SiGe Technology

One of the key functions of transmit and receive modules with a single antenna is the separation of the weak receive signal (RX) from the strong transmit signal (TX). In state-of-the-art FMCW radar MMICs, this function is usually implemented using passive devices, which have relatively large physical dimensions compared to the chip area and exhibit insertion losses. In this letter the design of an active quasi-circulator (QC) is presented with a special emphasis on TX/RX isolation. An analysis is presented to aid in the circuit design, so that the desired isolation requirements can be achieved. The implemented active QC is fabricated in a 200 GHz fT Silicon-Germanium (SiGe) HBT technology. On-wafer measurements show a TX/RX isolation of 16 dB over a bandwidth of 8 GHz. The measured insertion loss for the TX and the RX signal is less than 1 and 1.5 dB, respectively.

A New Active Quasi-Circulator Structure with High Isolation for 77-GHz Automotive FMCW Radar Systems in SiGe Technology

A new structure of an active quasi-circulator(QC) is presented to separate the weak receive signal(RX) from the transmit signal (TX) in 77-GHz monostatic FMCW radars. Process variations, antenna mismatch as well as parasitics in the circuit degrade the TX/RX isolation. A control unit in form of a W-band impedance tuner is used for compensating these effects. The QC with impedance tuner is fabricated in a 200-GHz fT Silicon-Germanium (SiGe) HBT technology. Based on on-wafer measurements, a TX/RX isolation of 50 dB at 77GHz is demonstrated. Over a bandwidth of 1 GHz the isolation remains more than 30 dB. The insertion loss for the TX-path and the RX-path is around 0 dB and 1 dB, respectively. Now the tuner facilitates the change of the QC performance during one frequency ramp. With respect to isolation, satisfying results for automotive FMCW radars can be shown from 65-85 GHz.

Characterization of Differential Transmission Lines for Integrated Millimeter-Wave Applications

This letter focuses on the characterization of differential transmission lines (T-lines) typically used in millimeter-wave integrated circuits. Common- and differential-mode propagation constants were calculated and validated in two experimental steps. A four-port scattering parameter (S-parameter) measurement followed by a multi-line calibration was performed. In addition, several two-port S-parameter measurements were conducted using a set of three marchand baluns. Comparison of the values extracted from simulations and two experiments shows very good agreement over a broad frequency range from 65 to 170 GHz.

A Differential Pair-Based Direct Digital Synthesizer MMIC With 16.8-GHz Clock and 488-mW Power Consumption

This paper presents a low-power, high-speed direct digital synthesizer monolithic microwave integrated circuit in a SiGe bipolar technology with 8-bit phase and 6-bit amplitude resolution. The phase-to-amplitude mapping circuit is implemented as a differential pair in saturation. The use of a modern SiGe bipolar technology enables both a low power consumption of 488 mW at a 3.3-V supply and a high clock frequency of 16.8 GHz; here, the maximum output frequency is 8.3344 GHz and the frequency resolution is 65.625 MHz. A spurious-free dynamic range (SFDR) between 47-20 dBc is achieved. First Nyquist zone SFDR, narrowband SFDR, and frequency-modulation measurements of the signal are shown and discussed. The chip is fabricated in a 0.35-¿m 200-GHz fT SiGe bipolar technology and occupies only 1128 × 1028 ¿m2. The chip is mounted on a printed circuit board for measurement.

An active quasi-circulator with a passive linear TX-path for 77-GHz automotive FMCW radar systems in SiGe technology

An active quasi-circulator (QC) for transmit (TX) and receive (RX) signal separation in monostatic FMCW 77-GHz radar transceivers is presented with special emphasis on linear behavior in the TX-path. To increase the compression point in the TX-path, the conventional structure of an active QC circuit is modified. A transformer is used to transfer the transmit power to the antenna, which performs DC decoupling at the antenna port at the same time. The circuit is implemented in a 200-GHz fT Silicon-Germanium (SiGe) HBT technology and measured onwafer. Since there is no active device in the TX-path, there is no compression of the transmitted signal, which has been verified up to 10dBm input power. The TX/RX isolation is maintained independent of the transmit power. The measured return loss at 77 GHz is below 10 dB at each port, whereas the transmission parameter for the TX signal and RX signal are -7.2 dB and 2.7 dB, respectively. The TX/RX isolation is about 23 dB over a bandwidth of 8 GHz.

An active quasi-circulator with controllable leakage canceler and passive TX path for 77-GHz automotive FMCW radar systems in SiGe technology

A modified structure of an active quasi-circulator (QC) is proposed for receive signal (RX) and transmit signal (TX) separation in 77-GHz monostatic FMCW radars. The circuit includes an impedance tuner, operating as leakage canceler, which performs compensation for process variations, parasitics of transistors as well as antenna mismatch. Additionally, the TX path is designed to be passive, to avoid any compression in the transmit signal. The QC is fabricated in a 200-GHz fT Silicon-Germanium (SiGe) HBT technology. On-wafer S-Parameter measurements show an isolation of 43 dB at 78 GHz. The insertion loss for the TX-path is around 7dB, whereas the gain in the RX-path is around 3 dB. Due to the tuner, the center frequency of the isolation can be varied from 67 GHz to 85 GHz.

77-GHz active quasi-circulator based Doppler radar with phase evaluation for object tracking

A 77-GHz Doppler shift radar is demonstrated based on an Active Quasi-Circulator (QC) monostatic approach. The QC system includes a leakage canceler as well as a modulator for time division IQ switching. A flexible decimation chain, implemented in an FPGA, facilitates the use of a low cost ADC with moderate SNR performance. By analyzing the drift behavior of the system, the parameters for an appropriate high pass filter can be obtained. The system is capable of measuring Doppler shift frequencies from 0.05 Hz up to around 4 kHz. By means of a phase evaluation algorithm, it is possible to observe objects with varying velocities. Finally, the system has been verified with a breathing test, where the depth and the frequency of the breath can be determined accurately.

Analysis of leakage in a 77-GHz Quasi Circulator based transceiver with time division IQ switching

A detailed analysis of leakage in a 77-GHz Quasi Circulator (QC) based transceiver is performed. The evaluated system includes an IQ modulator in the LO path for time division IQ switching. A leakage canceler, realized as a varactor based W-band impedance tuner, is employed in the transceiver. The leakage canceler can be controlled based on the DC-offset of the mixer. With an appropriate model of the occurring leakage, the relation between DC-offset and different leakage sources can be explained. Furthermore, the limitations of canceling the DC-offset in the system are derived. A simulator has been developed to demonstrate the effects of the non ideal IQ modulator as well as the nonlinear characteristic of the impedance tuner. This facilitates the understanding of the DC-offset output behavior. The model as well as the simulation have been verified based on on-wafer measurements.

High bandwidth of 8 GHz active quasi-circulator with integrated digital leakage canceler in SiGe BICMOS technology for automotive radar systems

An active quasi-circulator (QC) with high bandwidth is proposed for monostatic FMCW automotive 77-GHz radar sensors. The QC is build around a commonly used differential LNA. As the layout of the QC is symmetrical in contrast to traditionally active QCs, the system is robust and offers a high bandwidth in respect with transmit (TX) to receive (RX) signal isolation. A single ended to differential conversion is also provided by the proposed structure without any additional losses, which directly improves the noise figure (NF) performance of the receiver. Effects like process variations and antenna mismatch can be compensated by a digitally controlled CMOS based impedance tuner acting as a leakage canceler. The system has been fabricated in a 250-GHz fT Silicon-Germanium (SiGe) BiCMOS technology. The QC performance is demonstrated based on on-wafer measurements. Over a 10-GHz bandwidth, the receiver gain is higher than 7 dB, whereas the insertion loss of the passive TX-path is around 6.5 dB. Assuming an isolation of 30 dB, the bandwidth remains 8 GHz, which is sufficient for automotive radar systems.