A Single-Inductor Step-Up DC-DC Switching Converter with Bipolar Outputs for Active Matrix OLED Mobile Display Panels

Abstract

Of the different flat panel displays that can meet the increasing requirements of customers, the active matrix OLED (AMOLED) display is a strong candidate for mobile applications owing to its high resolution, low power consumption and low cost. AMOLED panels, however, usually require multiple power supplies with different regulated voltages. Therefore, step-up switching converters that can supply multiple outputs for this application are important.A single inductor bipolar output (SIBO) converter, shown in Fig. 7.4.1, is presented in this paper to power an AMOLED display for TDMA (GSM) mobile sets, which requires both positive and negative voltages with a gap of 10 to 12V. This converter reduces the overall size and cost of a mobile set. The most critical specification for this application is the line transient response of the positive supply, V OP , which can seriously affect the display by changing V gs of M p4 if it is not fast enough, thus changing the current I OP through the AMOLED. Based on experimentally verified data, the average variation of V OP should be strictly less than 4mV within 51.2µs of a 0.5V fluctuation in the battery voltage, V g , to avoid visible flicker on the display as illustrated in Fig. 7.4.1. Its switching ripple should also be under 30mV for a clean image. However, for the negative output V ON , its variation only affects V ds of M p4 , and hence, its line transient and ripple specifications are not as severe. Because of the stringent requirements for V OP , some chipmakers have attempted to obtain the V OP with an LDO [1] regulator, which creates a trade-off between reduced efficiency and increased cost and area.The converter in Fig. 7.4.1 is a combination of two converters: V OP is obtained from a boost operation employing modified comparator control (MCC) and V ON from a charge-pump circuit with PIcontrol. The control of the power switches is simplified compared to the topologies reported in [2] by delivering charge to all outputs at every switching cycle with priority given to V OP . The charge remaining after transferring charge to V OP is used to control the PWM signal for M n1 . Therefore, the effect of battery voltage fluctuations can be seen on V ON but is very small on V OP since V OP is controlled by a comparator while V ON is controlled by a PI loop. An additional high voltage output V H (= |V ON | + V D1 ) is intentionally generated to supply all gate drivers and to bias the bodies of the power PMOS transistors to reduce the sizes of the switches. The freewheeling switch M p3 is active in the discontinuous-conduction mode (DCM) with the zero-inductor-current detection technique reported in [3]. Consequently, the size and the conduction loss of M p3 are smaller than those of the one in the converter of [4]. .4.3 shows the peak current sensing method used in this converter. The circuit can accurately sense the peak inductor current I peak both in DCM and CCM. Normally, I peak is obtained from the on-voltage across M n1 (in Fig. 7.4.1). However, in this SIBO, the curren...

Adaptive pseudo-continuous conduction mode operation schemes and circuit designs for single-inductor multiple-output switching converters

“…Among prior arts, there are mainly two types of PCCM switching schemes. First, the inductor is charged only once in one switching cycle and discharged multiple times to different outputs [12,18]. This type of the operation scheme is called single-charge scheme.…”

“…By timesharing a single inductor L and a primary power switch S X , multiple power outputs can be regulated independently and simultaneously, leading to significant reduction on cost, complexity, PCB footprint and system form factor. Because of these cost-effective features, the application of SIMO power converters has been proliferating, spanning from hybrid power source units [8], energy harvesting systems [9,10] to light-emitting diode (LED) backlighting [11,12] and electronic paper displays [13]. As SIMO converters circuit architectures and control schemes are still relatively new, they remain as the primary focus in these early stage research literatures [4][5][6][7][8][9][10][11][12][13].…”

“…Because of these cost-effective features, the application of SIMO power converters has been proliferating, spanning from hybrid power source units [8], energy harvesting systems [9,10] to light-emitting diode (LED) backlighting [11,12] and electronic paper displays [13]. As SIMO converters circuit architectures and control schemes are still relatively new, they remain as the primary focus in these early stage research literatures [4][5][6][7][8][9][10][11][12][13]. However, driven by strong commercialization needs, performance enhancement on each design specification of such a converter starts to become critical.…”

A 0.791mm² fully on-chip controller with self-error-correction for boost DC-DC converter based on Zero-Order Control

“…As a result, a DC offset error occurs, which is corrected using an additional integral shunt loop in [2]. To guarantee stable operation, however, this shunt loop should be slower than the main control loop [6]; therefore the shunt loop requires a large off-chip capacitor. Instead, in the proposed method, the DC offset error correction is done simply through proposed V ST adding block with new control scheme, as shown in Fig.2.…”

A single-inductor bipolar-output converter with 5 mV positive voltage ripple for active matrix OLED

“…A conventional comparator-controlled method in single-inductor multiple-output (SIMO) converters with an ordered power-distributive control is proposed for the multi-outputs at light loads [11]. This technique is easy to extend to multiple outputs and the low cross-regulation can be guaranteed.…”