LTC2440 Datasheet, PDF (25/28 Pages) Linear Technology – 24-Bit High Speed Differential delta-sigma ADC with Selectable Speed/Resolution

LTC2440
APPLICATIO S I FOR ATIO
combinations of oversample ratio and clock frequency.
Understanding these properties is the key to fine tuning
the characteristics of the LTC2440 to the application.
multiples (up to the modulator sample rate of 1.8MHz)
exceeds 120dB. This is 8 times the maximum conversion
rate.
Maximum Conversion Rate
The maximum conversion rate is the fastest possible rate
at which conversions can be performed.
First Notch Frequency
This is the first notch in the SINC⁴ portion of the digital
filter and depends on the f_o clock frequency and the
oversample ratio. Rejection at this frequency and its
Effective Noise Bandwidth
The LTC2440 has extremely good input noise rejection
from the first notch frequency all the way out to the
modulator sample rate (typically 1.8MHz). Effective noise
bandwidth is a measure of how the ADC will reject wideband
input noise up to the modulator sample rate. The example
on the following page shows how the noise rejection of the
LTC2440 reduces the effective noise of an amplifier driv-
ing its input.
Table 6
Oversample Ratio ADC ENOB Maximum Conversion Rate First Notch Frequency
Effective Noise BW
–3dB point(Hz)
(OSR)
Noise* (V_REF = 5V)* Internal
9MHz clock
External
f_o
Internal
9MHz clock
External
f_o
Internal
9MHz clock
External
f_o
Internal
9MHz clock
External
f_o
64
23µV
17
3515.6
F_o/2560
28125
F_o/320
3148
F_o/2850
1696
F_o/5310
128
3.5µV 20
1757.8
F_o/5120
14062.5 F_o/640
1574
F_o/5700
848
F_o/10600
256
2µV 21.3
878.9
F_o/10240
7031.3 F_o/1280
787
F_o/11400
424
F_o/21200
512
1.4µV 21.8
439.5
F_o/20480
3515.6 F_o/2560
394
F_o/22800
212
F_o/42500
1024
1µV 22.4
219.7
F_o/40960
1757.8 F_o/5120
197
F_o/45700
106
F_o/84900
2048
750nV 22.9
109.9
F_o/81920
878.9
F_o/1020
98.4
F_o/91400
53
F_o/170000
4096
510nV 23.4
54.9
F_o/163840
439.5
F_o/2050
49.2 F_o/183000 26.5 F_o/340000
8192
375nV 24
27.5
F_o/327680
219.7
F_o/4100
24.6 F_o/366000 13.2 F_o/679000
16384
250nV 24.4
13.7
F_o/655360
109.9
F_o/8190
12.4 F_o/731000
6.6 F_o/1358000
32768
200nV 24.6
6.9
F_o/1310720
54.9
F_o/16380
6.2 F_o/1463000 3.3 F_o/2717000
*ADC noise increases by approximately √2 when OSR is decreased by a factor of 2 for OSR 32768 to OSR 256. The ADC noise at OSR 128 and OSR 64
include effects from internal modulator quantization noise.
sn2440, 2440fas
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