Low Noise Regulator with Adaptive Low-Pass Filter

This paper proposes a low-noise regulator with an adaptive low-pass filter (ALPF), consisting of a front-stage voltage regulator, an adaptive low-pass filter, and a back-stage voltage regulator. The front-stage voltage regulator samples the reference voltage to ensure stable DC output. The adaptive low-pass filter maintains a constant cutoff frequency (Ft) despite temperature variations, effectively filtering out noise from both the front-stage and reference voltage. The back-stage voltage regulator samples the filtered low-noise signal, producing a stable, low-noise regulated output. Both the front-stage and back-stage voltage regulators employ a chopping structure to mitigate noise and offset voltage in the error amplifier. The low-pass filter includes a capacitor and a temperature-dependent resistor to stabilize the cutoff frequency with temperature changes. The design is implemented using a 0.18 μm process, with simulation results demonstrating a noise integrated value of 4.8 μV in the 0.1 Hz–10 Hz range and 20.8 μV in the 10 Hz–100 kHz range, with a quiescent current of 40 μA. The structure is also more effective at reducing high-frequency noise from the reference input voltage.