High Performance Asymmetric Coupled Line Balun at Sub-THz Frequency

Abstract

In this paper, we report a high-performance balun with characteristics suitable for future broadband sub-THz differential circuits. The idea of the balun is based on three asymmetric coupled lines, which enhance the odd mode capacitances to equalize the even/odd mode phase velocities. The inner line of the three asymmetric coupled lines is configured to form the open stub ( λ /2), while the outer lines form short stubs ( λ /4). To further reduce the phase imbalance, the short stubs in one of the arms of the balun are connected with vias and a lower metal layer. The balun is developed using the standard 130-nm SiGe BiCMOSback-end process and EM simulated with ADS momentum and Sonnet. The −10-dB reflection coefficient (S 11 ) bandwidth of the balun is 136 GHz (88–224 GHz). It shows insertion loss (including RF pads) <1.5 dB, phase imbalance <7 degrees, and amplitude imbalance <1 dB at 94–177 GHz. Furthermore, a scaled-down version of the balun operates on the WR-6, WR-5, and WR-4 frequency bands without significant degradation in its performance. Such characteristics of the balun make it an ideal candidate for various broadband differential circuits.

A Wideband High-Gain Power Amplifier Operating in the D Band

“…Several on-chip, transformer-based and Marchand Baluns that perform the required single to differential conversion at the D-band, have been published recently [2], since the measurements for differential circuits in sub-THz frequencies are, in general, performed single-ended [10]. Figure 4 shows the 3D view of the MBL used in this work and based on [11]. The signal path is realized with the top copper layer (M6) for the minimization of the resistive losses and the capacitive coupling to ground, while the bottom layer (M1) is used as return path, providing a well-defined reference ground plane and thus enforcing the accuracy of its EM simulation.…”

Active Balun with Center-Tapped Inductor and Double-Balanced Gilbert Mixer for GNSS Applications

“…A passive balun for the K band (18.4-32.2 GHz) composed of a pair of coupled spiral inductors has dimension of only 410 µm × 180 µm [10]. A passive balun can be implemented as a transformer [8,11,14,20,25] or as coupled transmission lines [11,18,26,27]. Balun circuit solutions using coupled transmission lines are solutions with very wide bandwidths.…”

“…Balun circuit solutions using coupled transmission lines are solutions with very wide bandwidths. The bands of the coupled transmission-line baluns presented in previous articles [18,26,27] are as follows: 50-67 GHz (bandwidth of 17 GHz), 29-46 GHz (bandwidth of 17 GHz) and 88-224 GHz (bandwidth of 136 GHz).…”

A Fully-Printed CRLH Dual-Band Dipole Antenna Fed by a Compact CRLH Dual-Band Balun

“…Isolation between two bands can be better by making an SIR (Step impedance resonator) feedback loop between the two output branches by Li [ 20 ]. Multiple loops causing the phase difference are formed through layers with vertical lines as bridges [ 21 ]. Kahng et al proposed a CRLH-based balun for common-mode current indicator which is employed in the chip and PCB EMC (Printed circuit board electromagnetics compatibility) problems.…”