Compact low phase imbalance broadband attenuator based on SiGe PIN diode

A compact low phase imbalance broadband attenuator has been proposed and fabricated in a standard 0.18-um SiGe BiCMOS process. This inductor-less attenuator takes advantage of high linearity and low junction capacitance of the SiGe PIN (P-type Intrinsic N-type) diodes to achieve comparable performances with its GaAs counterparts. Symmetrical placement of PIN diodes in reference and attenuation paths ensures low phase imbalance between different attenuation states. T-type resistive network is employed for small chip size and separate DC biases for each bit are implemented to minimize leakage through the parasitic diodes between P-sub and N-well of the PIN diodes. This attenuator, including pads, occupies 0.85×0.412 mm². It has 8 attenuation states with a 1 dB step. The average insertion loss is 9.2 dB for the reference path and the phase variation for different states is −4.1 to 2.4°, which is the lowest among recently reported broadband attenuators.