Abstract
In this paper, a W-band mixer integrated circuit (IC) with high image rejection ratio (IRR) is presented, compensating for the amplitude and phase mismatches between the I and Q channels in the image rejection mixer (IRM) using RF buffer amplifiers. It is shown by analysis and simulation that the signal coupling between the I and Q channels in the IRM can generate mismatches which can severely degrade the IRR, even though other circuit components are symmetrically designed so as not to induce mismatches. The coupling between two channels can become serious, especially in millimeter-wave IRM ICs where the circuit components are laid out in close proximity to reduce the chip size. It is also shown that poor isolation of millimeter-wave couplers can seriously degrade IRR. In this work, we employ an RF buffer amplifier at the RF port of the resistive mixer to compensate for the amplitude and phase mismatches. The designed W-band IRM IC is fabricated in a 0.1-μm GaAs pHEMT process. Measurements show that the bias tuning of the RF buffer amplifiers can minimize the mismatches and improve the IRR by up to 35 dB at RF from 91 to 95 GHz at an IF of 50 MHz. The IRM exhibits an IRR of 19.2-47.9 dB with conversion loss of 7.9-9.2 dB, which belongs to the highest IRR among the reported IRMs in the W-band.
Highlights
The millimeter-wave band (30–300 GHz) is being actively studied for various applications because it provides a wide bandwidth for high-speed wireless communications
The image is located at a frequency that is in either the upper sideband (USB) or lower sideband (LSB) of the local oscillator (LO) frequency by intermediate frequency (IF), The associate editor coordinating the review of this manuscript and approving it for publication was Pu-Kun Liu
Mismatches can be produced by the imperfect performance of radio frequency (RF), LO and IF couplers, variations in the circuit components such as transistors, resistors and capacitors, and asymmetrical layout. We introduce another cause of mismatches, the signal coupling between the I and Q channels which can be induced by the substrate between the closely placed circuit components and the poor isolation of the couplers in the millimeter-wave integrated circuit (IC)
Summary
The millimeter-wave band (30–300 GHz) is being actively studied for various applications because it provides a wide bandwidth for high-speed wireless communications. It allows a short wavelength for high-resolution radar and imaging applications such as security, medical imaging, and virtual reality (VR) applications [1], [2]. The image problem is one of the biggest issues with the practical use of the mixer. The image is located at a frequency that is in either the upper sideband (USB) or lower sideband (LSB) of the LO frequency by IF, The associate editor coordinating the review of this manuscript and approving it for publication was Pu-Kun Liu
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