Output Balun Research Articles

A 60 GHz mixer using 0.25 μm SiGe BiCMOS technology

AbstractIn this article, a 60 GHz band down‐conversion mixer for 60 GHz wireless personal‐area network is designed and fabricated on a chip using 0.25 μm SiGe:C BiCMOS process technology. To design this 60 GHz band mixer, architecture of double‐balanced mixer is used, including input and output balun circuits, which are composed of active elements. The results of the fabricated mixer measured between RF 57 and 63 GHz show conversion gain of 12.0–10.7 dB, LO to RF isolation and LO to IF isolation of more than 28 dB, and input P1dB of −17 to −18 dBm. The chip size of the manufactured mixer is 1.3 mm × 0.8 mm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3007–3009, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23887

Monolithic SiGe Up-/Down-Conversion Mixers with Active Baluns

The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on-chip 1 to 6 GHz up-conversion and 1 to 8 GHz down-conversion mixers using a 0.8 µm SiGe hetero-junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up-conversion mixer was implemented on-chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up-conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down-conversion mixer was implemented on-chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down-conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz.

A gallium~nitride push~pull microwave power amplifier

A highly efficient linear, broad-band AlGaN-GaN high electron-mobility transistor (HEMT) push-pull microwave power amplifier has been achieved using discrete devices. Instrumental was a low-loss planar three-coupled-line balun with integrated biasing. Using two 1.5-mm GaN HEMTs, a push-pull amplifier yielded 42% power-added efficiency with 28.5-dBm input power at 5.2 GHz, and a 3-dB bandwidth of 4-8.5 GHz was achieved with class-B bias. The output power at 3-dB gain compression was 36 dBm under continuous-wave operation. Along with the high efficiency, good linearity was obtained compared to single-ended operation. The second harmonic content of the amplifier was more than 30 dB down over the 4-8.5-GHz band, and a two-tone excitation measurement gave an input third-order intercept point of 31.5 dBm at 8 GHz. These experimental results and an analysis of the periodic load presented by the output balun suggest the plausibility of broad-band push-pull operation for microwave systems with frequency diversity.

Radio frequency coupling between an antenna and two unshielded parallel wires above a metal sheet-measurement precautions

An unshielded 1 m transmission line, made of two parallel wires suspended 0.1 m above a plane metal sheet, is illuminated in the VHF and UHF bands by a log-periodic dipole array (LPDA). A network analyzer is used to measure the voltage induced at one end of the line. The measured signal is compared to the predictions of a moment method numerical analysis, using the NEC code. The measured and predicted coupling are in reasonable agreement only once two measurement precautions are taken. First, the illuminating antenna has to be well-balanced to suppress common mode radiation from the coaxial cable connecting the transmitter to the antenna. Second, an output balun must be inserted between the unshielded transmission line and the coaxial cable to the network analyzer. This is needed to prevent common mode signals on the coaxial cable from contaminating the measurements. Besides these practical steps, it is also necessary to use physical insight and high frequency circuit theory to develop a good equivalent circuit of the output balun for use in the computational model.

Influence of imbalance on distortion in optical push-pull frontends

The influence of imbalance on second-order intermodulation distortion (IMD2) in optical push-pull frontends for subcarrier multiplex CATV applications is investigated theoretically and experimentally. The investigation focuses on imbalance introduced in either the photodiode, the push-pull amplifier, or the output balun, and expressions describing the overall IMD2 cancellation efficiency are derived. The developed theory is used to predict the IMD2 cancellation behavior of an optical push-pull frontend. Commercially available PIN photodiodes for CATV purposes and ferrite core transformers are characterised for phase and amplitude balance up to 1 GHz. The overall IMD2 cancellation efficiency of an optical push-pull frontend based on the best of these devices is calculated. The theory is finally verified experimentally with an optical push-pull frontend designed with the characterised photodiode and transformer. The improvement in IMD2 suppression obtained with the push-pull structure relative to a single-ended structure is in average 29 dB across the band from 47-862 MHz. The total IMD2 suppression obtained for the frontend is between 60 dBc and 79 dBc at an average optical input power of 1 mW and with an optical modulation index (OMI) of 35 percent per carrier in a two-tone setup,.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Generation of balanced subnanosecond pulsesusing step-recovery diodes

A method for generating balanced subnanosecond pulses is described. By using pulsed bias techniques to excite a step-recovery diode via a conventional ferrite balun transformer, a balanced step waveform can be taken directly from the diode itself, eliminating the requirement for a broadband output balun transformer. The resulting pulses are suitable for applications in broadband antenna excitation, time-domain reflectometry and high-speed sampling bridges.