參數(shù)資料
型號: LTC2488CDE
廠商: LINEAR TECHNOLOGY CORP
元件分類: ADC
英文描述: 4-CH 16-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PQCC14
封裝: 4 X 3 MM, PLASTIC, MO-229WGED-3, QFN-14
文件頁數(shù): 16/28頁
文件大?。?/td> 427K
代理商: LTC2488CDE
LTC2488
23
2488f
APPLICATIONS INFORMATION
Normal Mode Rejection and Anti-aliasing
One of the advantages delta-sigma ADCs offer over
conventional ADCs is on-chip digital ltering. Combined
with a large oversample ratio, the LTC2488 signicantly
simplies anti-aliasing lter requirements. Additionally,
the input current cancellation feature allows external low
pass ltering without degrading the DC performance of
the device.
The SINC4 digital lter provides excellent normal mode
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (fS). The modulator
sampling frequency is fS = 15,360Hz while operating with
its internal oscillator and fS = FEOSC/20 when operating
with an external oscillator of frequency FEOSC.
When using the internal oscillator, the LTC2488 is designed
to reject line frequencies. As shown in Figure 16, rejection
nulls occur at multiples of frequency fN, where fN = 55Hz
for simultaneous 50Hz/60Hz rejection. Multiples of the
modulator sampling rate (fS = fN 256) only reject noise
to 15dB (see Figure 17), if noise sources are present at
these frequencies anti-aliasing will reduce their effects.
The user can expect to achieve this level of performance
using the internal oscillator, as shown in Figure 18.
Measured values of normal mode rejection are shown
superimposed over the theoretical values.
Traditional high order delta-sigma modulators suffer
from potential instabilities at large input signal levels. The
RSOURCE ()
0
+FS
ERROR
(ppm)
300
400
500
800
2488 F13
200
100
0
200
400
600
1000
VCC = 5V
VREF = 5V
VIN
+ = 3.75V
VIN
= 1.25V
FO = GND
TA = 25°C
CREF = 1F, 10F
CREF = 0.1F
CREF = 0.01F
RSOURCE ()
0
–FS
ERROR
(ppm)
–200
–100
0
800
2488 F14
–300
–400
–500
200
400
600
1000
VCC = 5V
VREF = 5V
VIN
+ = 1.25V
VIN
= 3.75V
FO = GND
TA = 25°C
CREF = 1F, 10F
CREF = 0.1F
CREF = 0.01F
Figure 13. +FS Error vs RSOURCE at VREF (Large CREF)
Figure 14. –FS Error vs RSOURCE at VREF (Large CREF)
VIN/VREF
– 0.5
INL
(ppm
OF
V
REF
)
2
6
10
0.3
2488 F15
–2
–6
0
4
8
–4
–8
–10
– 0.3
– 0.1
0.1
0.5
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
TA = 25°C
CREF = 10F
R = 1k
R = 100
R = 500
Figure 15. INL vs Differential Input Voltage and Reference
Source Resistance for CREF > 1F
INPUT SIGNAL FREQUENCY (Hz)
INPUT
NORMAL
MODE
REJECTION
(dB)
2488 F16
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
fN
0
2fN 3fN 4fN 5fN 6fN 7fN 8fN
fN = fEOSC/5120
Figure 16. Input Normal Mode Rejection at DC
相關(guān)PDF資料
PDF描述
LTC2488IDE#TR 4-CH 16-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PQCC14
LTC2488CDE#TR 4-CH 16-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PQCC14
LTC2488IDE 4-CH 16-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PQCC14
LTC2492CDE#TR 4-CH 24-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PDSO14
LTC2492CDE 4-CH 24-BIT DELTA-SIGMA ADC, SERIAL ACCESS, PDSO14
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