Design of Chip-to-PCB Matching Network for Millimeter-Wave On-Chip Transmitter and On-PCB Antenna

Design of chip-to-PCB interface at millimeter-wave (mm-Wave) frequencies is challenging due to the high inductance introduced of bonding wires and the high sensitivity to parasites at this frequency band. The smaller space between elements of the antenna array at mm-Wave also increases the design difficulties. To resolve these issues, stubs are adopted to match the antenna with the TX in series with bonding wires. In this paper, two matching networks with one and two stubs are demonstrated for a 2x2 phased array system. The first matching network employs a single stub to save the central PCB area, allowing for the placement of a large number of pads in a phased array system. The second matching network with two stubs increases the bandwidth and has much more tolerance to the PCB fabrication process variation. In designing the matching networks to achieve maximum power delivery, coupling between the four elements is inevitable due to the restricted area in the phased array system. As the networks are driven by multiple sources simultaneously, the characteristics of the networks change with the different driving conditions. We demonstrate and verify the inadequacy of S-parameter simulation for maximizing power transfer design by a simple coupled transmission line circuit. Therefore, the AC simulation which is closer to practical situations is applied in design of the matching network. Results from the 3D electromagnetic solver show that the matching network with a single stub has a bandwidth of 1.5 GHz, while the matching network with two stubs has a bandwidth of 3.3 GHz. The input reflection coefficient is below -10 dB at 28 GHz when the lengths of the transmission lines change within -0.03 to 0.05 mm for the single-stub matching network. While in the 2-stub matching network, the lengths can vary within -0.1 to 0.1 mm to achieve the same input matching condition.