the device through the specified temperature range, and returning to 25°C. This can be seen in Figure 8-6 to

Figure 8-8. Hysteresis can be expressed by Equation 1:

6

PRE

POST

HYST

NOM

| V

V

|

V

10

ppm

V

§

·

u

¨

¸

©

¹

(1)

where

• VHYST = thermal hysteresis (in units of ppm)

• VNOM = the specified output voltage

• VPRE = output voltage measured at 25°C pre-temperature cycling

• VPOST = output voltage measured after the device has cycled from 25°C through the specified temperature

range of –40°C to +125°C and returns to 25°C.

Thermal Hysteresis (ppm)

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

0

10%

20%

30%

40%

50%

Figure 8-6. REF7025QFKHR Thermal Hysteresis

Distribution (-40°C to 125°C)

Thermal Hysteresis (ppm)

0

10%

20%

30%

40%

50%

350

390

430

470

510

550

Figure 8-7. REF7012QDGKR Thermal Hysteresis

Distribution (-40°C to 125°C)

Thermal Hysteresis (ppm)

0

10%

20%

30%

40%

50%

0

10

20

30

40

Figure 8-8. REF7012QFKHR 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

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REF70

SNAS781G – OCTOBER 2020 – REVISED SEPTEMBER 2023

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