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Several types of DC-DC converters for active-matrix organic LED (AMOLED) displays have been introduced to date [1-4]. Single-inductor multiple-output (SIMO) converters with current-mode control have many advantages including reduced PCB space and less cost for mass-production due to the use of only one off-chip inductor to provide many outputs [1,2]. However, a load-dependent stability issue has to be addressed which is due to the output capacitance and an internal integrator with an error amplifier. Recently, in efforts to overcome the stability issue of current-mode control, load-independent control converters have been developed. Although this concept works well, the inductor-current sensing and artificial ramp generation for stability still make the controller complicated [3,4]. In addition, the freewheeling current control converter requires an extra power switch for freewheeling current flow, thereby lowering power efficiency . The vestigial current control converter, meanwhile, has weak points of requiring auxiliary output and an additional inductor, and thus consumes some additional power in the steady state . Besides the controller issue, the previous converters when operating with a large step-up ratio, usually have heavy voltage stress applied to the inductor, resulting in a low efficiency [1,4]. To overcome these problems, the proposed SIMO converter employs emulated absolute current hysteretic control, which uses full current information and is characterized by intrinsic high stability. The energy sharing capacitor is also used for high output voltage to reduce the voltage swing of the switching node and the associated loss. In addition, to balance the total energy across the inductor, the energy balancing capacitor is adopted.
Date of Conference: 19-23 Feb. 2012