The Design of Bidirectional Active Balun Chip Based on Power Modulation

Balun is used to realize the mutual conversion function from single-ended to differential signal. Balun can be divided into passive structure and active structure. The passive balun has a large area when the operating frequency is below 1GHz, on the other hand, the Q value of on-chip inductance is low and on-chip balun can cause great loss, which seriously affect the miniaturization design of the system. Active balun can realize high integration design, but traditional one is only limited to one-way signal transformation. For bidirectional conversion, it requires the application of switches to control multiple signals and introduce additional insertion loss and noise. This paper presents a bidirectional active balun working in 60MHz, whose circuit adopts switching mode of power modulation to realize bidirectional conversion between single-ended and differential conversion. The simulation result shows the phase difference of two output signals generated by single-ended inputs and differential outputs is about 18° at a temperature range from −40°C to 85°C, with error less than 1°. The signals generated by differential inputs and single-ended outputs can achieve gain balance. Its combined gain S21 is 1.1dB, and has more than 65dB reverse port isolation and certain linearity. Therefore, the simulation result shows that the bidirectional active balun meets the application requirements, and also verifies the correctness of theoretical analysis. It can improve the chip integration in system application, and has a wide application prospect