A 0.016mm2 144μW three-stage amplifier capable of driving 1-to-15nF capacitive load with >0.95MHz GBW

Abstract

High-color-depth LCD drivers require nF-range capacitors as the charge reservoirs to handle the glitch energy during the conversion of the DAC [1]. The reference buffers based on multi-stage amplifiers can enhance the precision under low-voltage supplies, but are exposed to instability when loaded by such large capacitive loads (C_L). Frequency compensation via damping-factor control [2] is capable of extending the C_L-drivability up to 1nF, however, at the cost of penalizing the power (426μW) and area (0.14mm²). Although recent works [3-4] have enhanced gain-bandwidth product (GBW) and slew rate (SR) showing better FOM_S (=GBW·C_L/Power) and FOM_L (=SR·C_L/Power), the C_L-drivability has not been improved (i.e., 0.8nF in [3] and 0.15nF in [4]). This paper describes a three-stage amplifier managed to afford particularly large and wide range of C_L (1 to 15nF) with optimized power (144μW) and die size (0.016mm²), being very suitable for compact LCD drivers [5] with different resolution targets. The design barriers are methodically surmounted via local feedback loop (LFL) analysis expanded from [6], which is an insightful control-centric method. Measured at 15nF C_L, the attained FOM_S (FOM_L) is >;4.48× (>;2.55×) beyond that of the state-of-the-art (Fig. 21.6.1).