A 55nm, Multiple-Loop, Fast-Transient, −76.2 dB Worst-Case PSRR LDO for High-End Audio Circuits

A low dropout regulator (LDO) is designed in 55nm CMOS technology. It is targeted for high-end audio applications, which present continuous-time as well as switched-capacitor building blocks. A multiple loop capacitor-less structure is proposed to cope with both high power supply rejection ratio (PSRR) and fast transient response. In particular, a folded flipped voltage follower (FFVF) output buffer presents a fast inner loop, needed to detach the error amplifier (EA) from the load capacitor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(CL)</tex> and drive this latter under fast transients. A variable resistance and adaptive biasing are developed to guarantee stability under all load conditions, including <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IL=0</tex> . Moreover, a slower high-gain loop is designed to set the output potential <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vₒᵤₜ</tex> , further reducing the output impedance and improving the PSRR, line and load regulation. The proposed LDO is implemented using IO high threshold transistors and provides an output voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vₒᵤₜ=1\ V</tex> from a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.2 V± 10%</tex> supply with a minimum possible dropout <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(Vdropᵐⁱⁿ)</tex> of 80 mV. It achieves a worst-case low-frequency PSRR of −76.2 dB under Montecarlo simulations (MC) and a recovery time of 142 ns when a load spike of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">800\ μ A</tex> is applied. Line and load regulation are 0.001 mV/V and 0.007 mV/mA. Moreover, the quiescent current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(Iq)</tex> is less than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20\ μ A</tex> at maximum <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IL</tex> .