108–316- and 220–290-GHz Ultrabroadband Distributed Frequency Doublers

An analysis and design of distributed frequency doublers is presented at millimeter-wave (mm-wave) frequencies, including the D-, G-, and H-bands. The phase condition required for coherent output summation in the distributed multipliers is analyzed to maximize the output power and bandwidth. Based on the analysis, two mm-wave distributed frequency doublers are designed and experimentally demonstrated. The first doubler combines three unit cells in a distributed manner, while the insertion phase is equalized between the input and output artificial transmission lines (T-lines). A differential quasi-cascode structure is proposed for each unit cell, which enables the bandwidth extension and chip-size reduction. The differential doubler exhibits a measured peak output power and a conversion gain of 3.5 dBm and -2.5 dB, respectively, at the output frequency of 165 GHz. At 276 GHz, the output power and conversion gain are 1.6 dBm and -6.2 dB, respectively. The doubler maintains high output power above -5 dBm from 108 to 316 GHz, which covers almost the entire D-, G-, and H-bands. The second doubler combines five single-ended cascode unit cells to improve the output power and conversion gain. A bandpass filter is employed at the output T-line for spurious signal suppression. The single-ended doubler shows a measured peak output and conversion gain of 5.5 dBm and 0.3 dB, respectively, at 240 GHz. The bandwidth for -5-dBm output is from 220 to 290 GHz. Both doublers occupy a small chip area of 0.23 and 0.27 mm², respectively, including all probing pads.