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参数资料
| 型号： | DC847A |
| 厂商： | Linear Technology |
| 文件页数： | 17/28页 |
| 文件大小： | 0K |
| 描述： | BOARD DELTA SIGMA ADC LTC2446 |
| 软件下载： | QuikEval System |
| 设计资源： | DC847A Design File DC847A Schematic |
| 标准包装： | 1 |
| 系列： | QuikEval™ |
| ADC 的数量： | 1 |
| 位数： | 24 |
| 采样率（每秒）： | 8k |
| 数据接口： | MICROWIRE?，串行，SPI? |
| 已用 IC / 零件： | LTC2446 |
| 已供物品： | 板 |
| 相关产品： | LTC2446CUHF#PBF-ND - IC ADC 24BIT 8CH HI SPEED 38QFN LTC2446IUHF#PBF-ND - IC ADC 24BIT 8CH HI SPEED 38QFN LTC2446IUHF#TRPBF-ND - IC ADC 24BIT 8CH HI SPEED 38QFN LTC2446CUHF#TRPBF-ND - IC ADC 24BIT 8CH HI SPEED 38QFN |
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LTC2446/LTC2447
24
24467fa
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 fo clock frequency and the oversample
ratio. Rejection at this frequency and its multiples (up to the
modulator sample rate of 1.8MHz) exceeds 120dB. This is
8 times the maximum conversion rate.
Effective Noise Bandwidth
The LTC2446/LTC2447 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 LTC2446/LTC2447 reduces the effective
noise of an amplifier driving its input.
Example:
If an amplifier (e.g. LT1219) driving the input of an
LTC2446/LTC2447 has wideband noise of 33nV/
√Hz,
band-limited to 1.8MHz, the total noise entering the
ADC input is:
33nV/
√Hz √1.8MHz = 44.3V.
APPLICATIO S I FOR ATIO
WU
U
When the ADC digitizes the input, its digital filter rejects the
wideband noise from the input signal. The noise reduction
depends on the oversample ratio which defines the effec-
tive bandwidth of the digital filter.
At an oversample of 256, the noise bandwidth of the ADC
is 787Hz which reduces the total amplifier noise to:
33nV/
√Hz √787Hz = 0.93V.
The total noise is the RMS sum of this noise with the 2
V
noise of the ADC at OSR=256.
√(0.93V)2 + (2uV)2 = 2.2V.
Increasing the oversample ratio to 32768 reduces the
noise bandwidth of the ADC to 6.2Hz which reduces the
total amplifier noise to:
33nV/
√Hz √6.2Hz = 82nV.
The total noise is the RMS sum of this noise with the 200nV
noise of the ADC at OSR = 32768.
√(82nV)2 + (200nV)2 = 216nV.
In this way, the digital filter with its variable oversampling
ratio can greatly reduce the effects of external noise
sources.
Table 7. Performance vs Over-Sample Ratio
MAXIMUM
FIRST NOTCH
EFFECTIVE
–3dB
OVER-
CONVERSION RATE
FREQUENCY
NOISE BW
POINT (Hz)
SAMPLE
*RMS
ENOB
INTERNAL
INTERNAL INTERNAL
RATIO
NOISE
(VREF = 5V)
9MHz
EXTERNAL
9MHz
EXTERNAL
9MHz
EXTERNAL
9MHz
EXTERNAL
(OSR) LTC2446 LTC2447 LTC2446
LTC2447
CLOCK
fO
CLOCK
fO
CLOCK
fO
CLOCK
fO
64
23
V23V
17
3515.6
fO/2560
28125
fO/320
3148
fO/5710
1696
fO/5310
128
4.5
V
3.5
V
20.1
20
1757.8
fO/5120
14062.5
fO/640
1574
fO/2860
848
fO/10600
256
2.8
V2V
20.8
21.3
878.9
fO/10240
7031.3
fO/1280
787
fO/1140
424
fO/21200
512
2
V
1.4
V
21.3
21.8
439.5
fO/20480
3515.6
fO/2560
394
fO/2280
212
fO/42500
1024
1.4
V1V
21.8
22.4
219.7
fO/40960
1757.8
fO/5120
197
fO/4570
106
fO/84900
2048
1.1
V
750nV
22.1
22.9
109.9
fO/81920
878.9
fO/1020
98.4
fO/9140
53
fO/170000
4096
720nV
510nV
22.7
23.4
54.9
fO/163840
439.5
fO/2050
49.2
fO/18300
26.5
fO/340000
8192
530nV
375nV
23.2
24
27.5
fO/327680
219.7
fO/4100
24.6
fO/36600
13.2
fO/679000
16384
350nV
250nV
23.8
24.4
13.7
fO/655360
109.9
fO/8190
12.4
fO/73100
6.6
fO/1358000
32768
280nV
200nV
24.1
24.6
6.9
fO/1310720
54.9
fO/16380
6.2
fO/146300
3.3
fO/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.
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