Third-order tunable-phase asymmetric crosscoupled oscillator

Here, the authors show that an asymmetric cross-coupled oscillator can be used to achieve independent-phase tunable outputs. In particular, a third-order cross-coupled oscillator, with non-balanced loads, is studied and expressions for its start-up condition, oscillation frequency, phase-shift between its two outputs as well as their amplitude ratio are derived. From these expressions, it is found that independent tuning of these design specifications is possible and a voltage-controlled phasetunable oscillator can be achieved. As a consequence of the non-balanced loads, the tail biasing current is not equally split between the two cross-coupled transistors. However, a design procedure that enables the equal splitting of the current is proposed and validated. Simulations of a prototype in a 0.18 μm CMOS process are given and experimental results with discrete transistors verify the correctness of the theory. © The Institution of Engineering and Technology 2019.