New Breed of Ultra Low Noise Regulators
Update (6/30/14): Added TI LP5907, reviewed noise figures.
Update (2/1/14): Added the ADM7150/ADM7151 which is now at the top of the pack.
Update (01/29/13): Revised the noise density numbers
Update (8/27/12): Added the new TI TPS7A4700 regulator to the table. This device can source up to 1 A of current and ranks on top of the list. Also please ignore the noise density numbers, I need to revise them. Look at the RMS noise values.
The table below compares the noise level of some regulators used in current DIY modules vs a new breed of regulators that are used in portable consumer devices such as cell phones.
Just like phase noise in clocks, it is difficult to compare noise values among linear regulators because there is no common ground in specifying noise figures. Some companies report noise density, others RMS V noise, and yet others % of Vout. The frequency range for the reported noise figures also varies from company to company. Thus it is required to convert spec numbers to a common measuring unit. I chose to convert everything to “Noise Density” in nV/Sqrt(Hz) numbers. In order to understand the relationship between RMS noise and noise density, you can watch this video tutorial: http://www.youtube.com/watch?v=ywChrIRIXWQ [or here]
The noise density numbers are taken off the noise density spectra charts in the data sheets (D) or when not available from the datasheet they are calculated (C) in accordance to the relationship presented in the video above. They have been further normalized to a bandwidth of 100KHz. The number represents the “tail” of the noise spectrum which is typically a flat line.
The first two rows are application notes indicating the noise density value of the noise floor. AN51 is a discrete design using a ZETEX voltage reference. LM723 is an old part used in older designs. Newer monolithic designs have the added advantage that they are also very low dropout (LDO).
The comparison suggests that whether using a discrete design or state of the art monolithic regulators, we are very close to the measurable noise floor (~14 nV seems the best regulators so far…).
For the diyer, these devices are very small and maybe very hard to solder, especially the micro SMD bump package.
|Regulator||Used in||Max Current
|BW for noise spec||Noise Density
|AN124||Noise floor||0.16 (peak)||0-10Hz||1? (not enough data)|
|ADM7150/7151||Discussion: [link]||800||1.6||10-100K||5.1(C), 1.7(D)|
|LP5907||diyinhk ES9018K2M||250||6.5||10-100K||21(C), 15(D)|
|LP5900||Lorien XMOS||150||6.5||10-100K||21(C), 12(D)
|ADM7160||New Product (looks very similar to ADP151)||200||9||10-100K||24(D)
|ADP151||Amanero USB, Ian’s FIFO||200||9||10-100K||28(C), 22(D)
|LT1763, LT1761, LT1762||Buffalo II (LT 1763)||500||20||10-100K||63(C), 40(D)|
|LT1963, LT1964||Musiland power mod
|LM317, LT1117||LCDPS, many low cost devices||1500, 800||99250||10-10K10-20K||3131 (?)3953 (?)|
As previously discussed, the noise density numbers are an approximation assuming that it is “flat” throughout the bandwidth of interest. The area under the noise density trace is the RMS noise figure. So basically, if we assume a square area and a bandwidth of 100 KHz, then the RMS Noise = Noise Density X SQRT(100,000) = Noise Density X 316
Note: the second noise figure for the LM317 comes from TNT-Audio [link]. There, it is measured at 250 uV for the ~20Khz bandwidth.