LTC2440IGN datasheet(20/28 Pages) LINER

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LTC2440

sn2440, 2440fas

APPLICATIO S I FOR ATIO

DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)

–140

–130

–120

–110

–100

2440 F12

–90

–80

Figure 12. LTC2440 Normal Mode Rejection (Internal Oscillator)

Table 5. OSR vs Notch Frequency (fN) with Internal Oscillator

Running at 9MHz

OSR

NOTCH (fN)

28.16kHz

128

14.08kHz

256

7.04kHz

512

3.52kHz

1024

1.76kHz

2048

880Hz

4096

440Hz

8192

220Hz

16384

110Hz

32768*

55Hz

*Simultaneous 50/60 rejection

the noise performance of the device is 200nVRMS with

better than 80dB rejection of 50Hz

±2% and 60Hz ±2%.

Since the OSR is large (32,768) the wide band rejection is

extremely large and the antialiasing requirements are

simple. The first multiple of fS occurs at 55Hz • 32,768 =

1.8MHz, see Figure 13.

The first NULL becomes fN = 7.04kHz with an OSR of 256

(an output rate of 880Hz) and FO grounded. While the

NULL has shifted, the sample rate remains constant. As a

result of constant modulator sampling rate, the linearity,

offset and full-scale performance remains unchanged as

does the first multiple of fS.

Figure 13. LTC2440 Normal Mode Rejection (Internal Oscillator)

DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)

–60

–40

1440 F13

–80

–100

1000000

2000000

–120

1.8MHz

–140

–20

REJECTION > 120dB

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