ADM7150: New (Low Noise) King of the Regulators
Analog Devices introduced a new 800 mA LDO with the lowest noise figures [link]:
- RMS Noise: 1.6 μV (10 Hz to 100 KHz)
- Noise Density: 1.7 nV√Hz (10 kHz to 1 MHz)
- Available in diy-friendly SOIC packages
- Price: ~$8 (quantity 1). The LT1763, also available in SOIC is ~$4
Here is comparing noise figures with other “favorite” regulators. Also, check out the table summary [link].
The low noise performance has been accomplished with a “new architecture” for linear regulators where the reference is first amplified and then buffered by a trans-impedance amplifier and filtered with an external capacitor [link, minute 34:30] The noise of the regulator can be further reduced by increasing the size of the bypass cap beyond the value recommended in the datasheet.
Here is an interesting graph [link] [link] showing the effect of the size of the bypass capacitor on the noise of the regulator. Notice the use of large value capacitors up to 10,000 uF (which is only practical for us diyers :-)).
From the datasheet:
The BYP capacitor is necessary to filter the reference buffer. A 1 µF capacitor is typically connected between BYP and GND.
Capacitors as small as 0.1 µF can be used; however, the output noise voltage of the LDO increases as a result. In addition, the BYP capacitor value can be increased to reduce the noise below 1 kHz at the expense of increasing the start-up time of the LDO.
Very large values of C BYP significantly reduce the noise below 10 Hz. Tantalum capacitors are recommended for capacitors larger than approximately 33 µF. A 1 μF ceramic capacitor in parallel with the larger tantalum capacitor is required to retain good noise performance at higher frequencies. Solid tantalum capacitors are less prone to microphonic noise issues.
More discussion at diyaudio [link] including comments from people involved in the design of the regulator