sx8725c Semtech Corporation, sx8725c Datasheet - Page 56

• Manufacturer Part Number: sx8725c
• Description: Zoomingadc For Sensing Data Acquisition
• Manufacturer: Semtech Corporation

Revision 1.01
© Semtech
As shown in
but reduces noise).
Figure 47
case, and, thus, the ADC thermal noise is below 16 bits.
As an example, consider the system where: GD
this case, the noise contribution V
= 6.4 μV (rms) at the input of the acquisition chain, or, equivalently, 0.85 LSB at the output of the ADC. Considering 0.2
V (rms) maximum signal amplitude, the signal-to-noise ratio is 90dB.
ADVANCED COMMUNICATIONS & SENSING
Analog
Inputs
Reference
Inputs
shows the distribution for the ADC alone (PGA1, 2, and 3 bypassed). Quantization noise is dominant in this
Equation
VSS
VREF
AC2
AC3
N.C.
N.C.
N.C.
N.C.
VBATT
VSS
VREF
VSS
Table 39. PGA Noise Measurement (n = 16bits, OSR = 512, N
Parameter
Output RMS noise(uV)
28, noise can be reduced by increasing OSR and N
January 2011
Figure 47. ADC Noise (PGA1, 2 & 3 Bypassed, OSR = 512, N
V
N,IN
N1
of PGA1 is dominant over that of PGA2. Using
V
S
80
60
40
20
REF,ADC
0
Figure 48. Total Input Referred Noise
-5
±
V
2
-4
Vin
Output Code Deviation From Mean Value [LSB]
IN
= 10 (GD
-3
PGA1
Page 56
-2
1
-1
= 1; PGA3 bypassed), OSR = 512, N
V
0
N1
PGA1
±
±
= 205
Vin
Voff
1
ZoomingADC for sensing data acquisition
2
PGA2
ELCONV
3
V
N2
PGA2
4
= 340
ELCONV
(increases the ADC averaging effect,
5
ELCONV
Equation 28, page
±
±
Vin
Voff
= 2, V
V
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= 2)
N3
PGA3
PGA3
= 365
ELCONV
REF
SX8725C
= 5V)
= 2, V
DATASHEET
55, we get: V
REF
±
±
Vin
Vref
V
= 5 V. In
IN,ADC
ADC
N,IN