Compact and Digitally Controlled D-Band Vector Modulator for Next-Gen Radar Applications in 130 nm SiGe BiCMOS

Abstract

Radar systems got very popular in sensing applications in the last two decades besides the traditional military sector. Nowadays, many applications favor multiple-input multiple-output (MIMO) radar over phased-array radar. Here, time-division multiplexing (TDM) and code-division multiplexing (CDM), like a phase-modulated continuous wave (PMCW), are well-known techniques. However, every method needs special components on the MMIC. In this article, a 125 GHz vector modulator (VM) circuit is presented, which can operate as a switchable amplifier in TDM systems, as a binary-phase modulator in CDM systems, and as a phase-shifter in phased-array systems. Based on simulations and S-parameter measurements, the VM itself and the three different operating modes are analyzed. We also present a technique to separate coupler imperfections from the S-parameter measurements to analyze the VM separately. We designed the VM with the B11HFC silicon-germanium technology ( f t / f max = 250/370 GHz), using both HBTs (heterojunction bipolar transistors) and CMOS transistors. Inside the VM, two cross-connected power amplifiers (PAs) are fed by an in-phase (I), and two cross-connected PAs are fed by a quadrature-phase (Q) signal. The four PAs are controlled by a 4-bit interface to switch them on or off, thus generating output signals in the range of 0 • to 360 • .

A Multipurpose D-Band Vector Modulator for FMCW and PMCW Sensing Applications in 130 nm SiGe

“…All results are deembedded such that the reference plane is in front of the BLC and behind the VM. We achieved this with a pad and balun back-to-back structure (presented in [59]). First, we measured the S-parameters of the back-to-back structure.…”

“…5). This uniformity is primarily determined by the accuracy of the BLC [59]. While the desired 45 • spacing is mostly achieved at both ends of the frequency it starts to diverge due to BLC limitations.…”

“…In our prior work, presented in [58], we introduced a vector modulator (VM) containing a purely digital interface, enabling rapid digital on-off switching and ≈ 45 • phase shifts compared to the capabilities outlined in [59]. In this article, we build upon the foundation laid by [58], enhancing its circuitry by incorporating three significant improvements featured in two newly introduced monolithic microwave integrated circuits (MMICs).…”

A D-Band Vector Modulator for Imaging Applications in 130nm SiGe

“…This transforms the low-pass behavior of the pads into a bandpass behavior. To measure the differential VM circuit with single-ended pads and probes, TRL-based baluns in a rat-race topology are used [45]. In the center of the chip is a TRLbased branchline coupler, which generates IQ signals, which are needed by the VM.…”

“…In an earlier article, we presented a vector modulator with a digital interface, which allows for time-division and phasecoded MIMO and phased-array techniques without using an external DAC [45]. The disadvantage of this modulator is that the beam cannot be steered during a frequency ramp since the phase jumps would increase the noise in the range spectrum.…”