SX8724C Datasheet, PDF (28/67 Pages) Semtech Corporation – ZoomingADC for sensing data acquisition

SX8724C
ZoomingADC for sensing data acquisition
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
7.7 Analog-to-Digital Converter (ADC)
The main performance characteristics of the ADC (resolution, conversion time, etc.) are determined by three
programmable parameters. The setting of these parameters and the resulting performances are described later.
fs :
OSR :
NELCONV :
Over-sampling frequency
Over-Sampling Ratio
Number of Elementary Conversions
7.7.1 Conversion Sequence
A conversion is started each time the bit Start or the Def bit is set. As depicted in Figure 14, a complete analog-to-
digital conversion sequence is made of a set of NELCONV elementary incremental conversions and a final quantization
step. Each elementary conversion is made of (OSR+1) over-sampling periods Ts=1/fs, i.e.:
T_ELCONV = (OSR+1) / f_S [s]
Equation 13
The result is the mean of the elementary conversion results. An important feature is that the elementary conversions
are alternatively performed with the offset of the internal amplifiers contributing in one direction and the other to the
output code. Thus, converter internal offset is eliminated if at least two elementary sequences are performed (i.e. if
NELCONV >= 2). A few additional clock cycles are also required to initiate and end the conversion properly.
Init
Elementary
Conversion
Conversion index 1
Offset
+
Elementary
Conversion
2
-
T_CONV
Elementary
Conversion
N_ELCONV-1
+
Elementary
Conversion
N_ELCONV
-
Figure 14. Analog-to-Digital Conversion Sequence
End
Conversion
Result
Note
The internal bandgap reference state may be forced High or Low, or may be set
to toggle during conversion at either the same rate or half the rate of the
Elementary Conversion. This may be useful to help eliminate bandgap related
internal offset voltage and 1/fs noise.
Revision 1.01
© Semtech
January 2011
Page 28
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