Wideband pHEMT Digital Attenuator With Positive Voltage Control Driver

This letter presents a wideband 6-bit digital attenuator with positive voltage driving capability. The designed attenuator solves the problem that traditional pseudomorphic high-electron-mobility transistor (pHEMT) attenuators need negative voltage control so that it can be better compatible with CMOS control signals. The frequency-select attenuation parallel (FSAP) network is utilized to improve high-frequency attenuation fluctuation and enable wideband flat attenuation characteristics. Simultaneously, this letter creatively proposed the lossy dc-block (LDB) network, which not only completes the dc blocking effect but also improves the low-frequency resonance in high attenuation state. The attenuator is implemented in the GaAs 0.25-
$\mu \text{m}$
pHEMT process. It demonstrates a 31.5-dB attenuation range with an increment of 0.5 dB. In the range of 0.05–6 GHz, the measured results showed that the root-mean-square (rms) attenuation and the phase error are within 0.8 dB and 16°, respectively, the reference state insertion loss (IL) is better than 2.3 dB, and the return loss is better than 15 dB for all the 64 attenuation states; the total chip size is 2 mm2.