Thermal Hysteresis (ppm)

120 130 140 150 160 170 180 190 200 210 220 230 240

0

10%

20%

30%

40%

50%

Figure 8-4. REF7025 Thermal Hysteresis

Distribution (-40°C to 125°C)

Thermal Hysteresis (ppm)

0

10%

20%

30%

40%

50%

0

10

20

30

40

Figure 8-5. REF7012 Thermal Hysteresis

Distribution (-40°C to 125°C)

8.4 Noise Performance

8.4.1 1/f Noise

1/f noise, also known as flicker noise, is a low frequency noise that affects the device output voltage which can

affect precision measurements in ADCs. This noise increases proportionally with output voltage and operating

temperature. It is measured by filtering the output from 0.1-Hz to 10-Hz. Since the 1/f noise is an extremely

low value, the frequency of interest needs to be amplified and band-pass filtered. This is done by using a

high-pass filter to block the DC voltage. The resulting noise is then amplified by a gain of 1000. The bandpass

filter is created by a series of high-pass and low-pass filter that adds additional gain to make it more visible

on a oscilloscope as shown in Figure 8-6. 1/f noise must be tested in a Faraday cage enclosure to block

environmental noise.

REF70xx

GND

OUTS

OUTF

VIN EN

VIN

CL

CIN

VREFP

High-pass Filter

FC = 0.07 Hz

Low Noise

Preamplifier

G = 1000

2

nd Order

Low-pass Filter

FC = 10 Hz

G = 1

2

nd Order

Low-pass Filter

FC = 10 Hz

G = 10

2

nd Order

High-pass Filter

FC = 0.1 Hz

G = 10

Scope

Copyright © 2017, Texas Instruments Incorporated

Figure 8-6. 1/f Noise Test Setup

Typical 1/f noise (0.1-Hz to 10-Hz) distribution can be seen in Figure 8-7.

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REF70

SNAS781E – OCTOBER 2020 – REVISED JULY 2022

Copyright © 2022 Texas Instruments Incorporated

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