Thermal Hysteresis - Cycle 1 (ppm)

0

5

10

15

20

25

0

22

44

66

88

110 132 154 176 198 220

Figure 8-5. Thermal Hysteresis Distribution

-40ºC to 125ºC, Cycle 1

Thermal Hysteresis - Cycle 2 (ppm)

0

2

4

6

8

10

12

14

16

18

20

22

24

0

22

44

66

88

110 132 154 176 198 220

Figure 8-6. Thermal Hysteresis Distribution

-40ºC to 125ºC, Cycle 2

8.5 Noise Performance

The reference pin output noise is categorized as low frequency and broadband noise. The following sections

describe these categories in detail.

8.5.1 Low-Frequency (1/f) Noise

Flicker noise, also known as 1/f 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. The noise is measured by filtering the output from 0.1 Hz to 10 Hz. The 1/f noise is an extremely

low value, therefore the frequency of interest must 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 8-7. Figure 8-8 shows the effect of flicker noise over 10 second. Flicker noise

must be tested in a Faraday cage enclosure to block environmental noise.

REF35-Q1

CIN

GND

VIN

EN

NR

VREF

GND

Optional

CL

High-pass

Filter

Fc = 0.07Hz

Low Noise

Preamplifier

G = 1000

2

nd Order

High-pass

Filter

Fc = 0.1Hz

G = 10

2

nd Order

Low-pass

Filter

Fc = 10Hz

G = 10

2

nd Order

Low-pass

Filter

Fc = 10Hz

G = 1

Oscilloscope

Supply

Buffer

Figure 8-7. Low-Frequency (1/f) Noise Test Setup

REF35-Q1

SNAS845 – AUGUST 2023

www.ti.com

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