LTC2440 Linear Technology, LTC2440 Datasheet - Page 25

• Manufacturer Part Number: LTC2440
• Description: 24-Bit High Speed Differential delta-sigma ADC
• Manufacturer: Linear Technology

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.
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 SINC
filter and depends on the f
oversample ratio. Rejection at this frequency and its
Table 6
*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.
Oversample Ratio ADC
16384
32768
(OSR)
1024
2048
4096
8192
128
256
512
64
750nV
510nV
375nV
250nV
200nV
Noise*
3.5µV
1.4µV
23µV
2µV
1µV
U
(V
REF
ENOB
21.3
21.8
22.4
22.9
23.4
24.4
24.6
17
20
24
U
= 5V)*
o
clock frequency and the
Maximum Conversion Rate
9MHz clock
4
3515.6
1757.8
Internal
878.9
439.5
219.7
109.9
54.9
27.5
13.7
W
portion of the digital
6.9
F
F
F
F
o
F
F
F
F
o
o
o
F
F
/1310720
External
o
o
o
o
/163840
/327680
/655360
o
o
/10240
/20480
/40960
/81920
/2560
/5120
U
f
o
9MHz clock
14062.5
First Notch Frequency
7031.3
3515.6
1757.8
Internal
28125
878.9
439.5
219.7
109.9
54.9
multiples (up to the modulator sample rate of 1.8MHz)
exceeds 120dB. This is 8 times the maximum conversion
rate.
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.
F
F
F
F
F
F
F
F
External
o
F
F
o
o
o
o
o
o
o
/16380
o
o
/1280
/2560
/5120
/1020
/2050
/4100
/8190
/320
/640
f
o
9MHz clock
Internal
3148
1574
98.4
49.2
24.6
12.4
Effective Noise BW
787
394
197
6.2
F
F
F
F
o
F
F
F
F
o
o
o
F
F
External
/1463000
o
o
o
o
/183000
/366000
/731000
o
o
/11400
/22800
/45700
/91400
/2850
/5700
f
o
9MHz clock
Internal
1696
LTC2440
26.5
13.2
848
424
212
106
6.6
3.3
53
–3dB point(Hz)
sn2440, 2440fas
F
F
F
F
F
F
F
F
F
o
o
o
o
o
F
/1358000
/2717000
External
o
o
o
o
/170000
/340000
/679000
o
25
/10600
/21200
/42500
/84900
/5310
f
o