## 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 (mA) |
RMS Noise Vout=3.3 (uV) |
BW for noise spec | Noise Density nV/Sqrt(Hz) @100KHz |

AN124 | Noise floor | 0.16 (peak) | 0-10Hz | 1? (not enough data) | |

AN83 | Noise floor | 0.5 | 10-100K | 1.6(C) | |

ADM7150/7151 | Discussion: [link] | 800 | 1.6 | 10-100K | 5.1(C), 1.7(D) |

TPS7A4700 | 1000 | 4.0 | 10-100K | 12(C), 12(D) | |

LP8900 | 200 | 6 | 10-100K | 19(C), 25(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) |

AN51 | 350 | 3 | 10-22K | 43 | |

LM723 | 150 | 2.5 | 100-10K | 79 | |

LT1763, LT1761, LT1762 | Buffalo II (LT 1763) | 500 | 20 | 10-100K | 63(C), 40(D) |

TPS79333 | Gamma-2 | 200 | 32 | 200-100K | 101 |

LT1963, LT1964 | Musiland power mod |
1500, 3000 | 40 | 10-100K | 126 |

LP2985 | Opus DAC | 150 | 30 | 300-50K | 190 |

TPS786xx | 1500 | 48 | 100-100K | 152 | |

LM340 | 1000 | 75 | 10-100K | 237 | |

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.

Further reading: http://hifiduino.blogspot.com/2010/03/comparing-noise-figures-in-linear.html

Very nice comparison, thank you! It is very interesting to notice the high performance of the 723 design, probably one of the oldest in this table, although is specified for 100Hz – 10 Khz.

Hey great overview solves alot of hassle like building own regs woithout dedicated tools and avoids the expensive regs (though they’re very good) from audiophile vendors!

My only problem I can’t purchase the AN 124 ?? I can’t find it nowhere – did some one meanwhile??

Jochen

AN124 is just an application note. I put it there as a reference point to show what is the minimum noise that can be reliably measured. The message being that ~ 1nV is the lower limit no matter what you do…

It shoould be intresting to add also : LT1117 LT1764

What about Micrel LDOs?

I am sure everyone is introducing new and lower noise LDO. The thing that “matters most” for audio is noise and current capability. We are now down to the single digit uV RMS noise in the 10 Hz to 100KHz frequency range. The other thing is transient response. Typically shown in a graph deep inside the data sheet.

I’m curious if anyone has experimented with using a 431 shunt with one of these low noise regulators. I see varying noise claims but 1-10Hz noise of a 431 seems lower than any of these series regs.

All those regs are good, but only for DVDD. I would never used them for AVDD. Here you need low noise of course, but also low impedance and flat frequency response. Any good quality shunt will better here. Among many I found Salas Reflector D the best.

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