A low-noise, low-drift D.C. voltage amplifier for use in D.C. voltage regulators

A low-noise, low-drift d.c. amplifier consisting of an IC voltage reference, a noninverting d.c. voltage amplifier, and a lowpass filter was developed for application in both low-noise voltage regulators and lownoise d.c. power supplies. The steps taken in the analysis and design, implementation, and testing of this circuit are presented. The circuit was designed for an operating temperature range of 0 to 70°C and a single supply voltage of 24 V (±20%). The reference voltage was 5 V, and the amplifier had a gain of 3 (with a 500 Hz bandwidth), resulting in a nominal output voltage of 15 V. The actual output noise voltage was measured to be 5.48 μV_rms as compared to the theoretical value of 1.75 μV_rms. The main source of this discrepancy me between the experimental and theoretical result was suspected to be the low-frequency noise of the reference. The worst case output voltage offset was measured to be 2.15 mV. The worst case output voltage drift (due to changes in temperature) was 0.3 mV (for a temperature range of 0-70°C). Finally, the maximum Line voltage regulation (for a supply voltage of 24 V ±20%) and quiescent current were found to be 0.7 mV and 9 mA, respectively.