In this paper, we present a distributed voltage controlled attenuator (VCA) featuring an extremely high power handling capability of 20 W. Theoretical analyses have been performed to simultaneously achieve a wideband, low insertion loss, and high attenuation dynamic range performance. Implemented in a commercial 0.25-μm GaN-on-SiC high electron mobility transistor (HEMT) technology, a 1-to 25-GHz VCA was measured to perform a dynamic range of 24 dB, an average insertion loss of 3.4 dB, and an average input 1-dB compressed power (P 1dB ) of 43 dBm across the frequencies of interest. To the best of the authors' knowledge, this paper presents the monolithic microwave integrated circuit (MMIC) VCA with the reported highest power handling capability in such compact chip area, while maintaining a nice operating bandwidth and dynamic range.distributed, gallium nitride (GaN), power handling capability, voltage-controlled attenuator, wideband
| INTRODUCTIONVoltage-controlled attenuators (VCAs) are commonly used in radio-frequency (RF) systems, such as protection of facilities in measurement setup, 1 phased-array transceiver systems, 2-6 and artificial satellite applications. [7][8][9] Unlike fixed attenuators that can only provide specific attenuation to the system, the attenuation level of VCAs is tunable to meet the requirement of different operating conditions. Due to the complex interactions between components integrated in communication systems, controlling power with high accuracy is essential to maintain proper operation of the system. VCAs are commonly used for gain controlling after power amplifiers, low-noise amplifiers, and array antennas. It not only controls the output power but also protects the receiving end. Such arrangement helps preventing the system to receive signals exceeding the critical level. Thus, a high power handling capability is necessary for the VCAs to avoid potential distortion during operation. Moreover, wide operating bandwidth, large dynamic range, and low insertion loss are also key parameters for the VCAs.Based on the operation mode, VCAs can be differed into two categories, namely, digital 10-15 and analog. [16][17][18][19] Digital VCA is also called digital step attenuator. Conventionally, digital VCA offers a high resolution but suffering from extreme phase differences between attenuation states induced by the internal capacitances of the devices. Moreover, the high complexity with design of the biasing network is also a critical issue for realizing digital VCA. As for the analog VCA, the issue regarding phase differences between the operating states can be mitigated. It also shows a less complexity in the circuit topology and biasing network comparing to the digital ones. This makes the analog VCA more feasible for integration in RF front-end systems requiring accurate control of the amplitude and phase differences.