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

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