
• For software triggered conversions, immediately follow the write to SC1 with a
Wait instruction or Stop instruction.
• For Normal Stop mode operation, select ADACK or an Alternate clock as the
clock source. Operation in Normal Stop reduces V
DD
noise but increases
effective conversion time due to stop recovery.
• There is no I/O switching, input or output, on the MCU during the conversion.
There are some situations where external system activity causes radiated or conducted
noise emissions or excessive V
DD
noise is coupled into the ADC. In these situations, or
when the MCU cannot be placed in Wait or Normal Stop mode, or I/O activity cannot be
halted, the following actions may reduce the effect of noise on the accuracy:
• Place a 0.01 μF capacitor (C
AS
) on the selected input channel to V
REFL
or V
SSA
. This
improves noise issues, but affects the sample rate based on the external analog source
resistance.
• Average the result by converting the analog input many times in succession and
dividing the sum of the results. Four samples are required to eliminate the effect of a
1 LSB, one-time error.
• Reduce the effect of synchronous noise by operating off the asynchronous clock, that
is, ADACK, and averaging. Noise that is synchronous to ADCK cannot be averaged
out.
34.6.2.4 Code width and quantization error
The ADC quantizes the ideal straight-line transfer function into 65536 steps in the 16-bit
mode.. Each step ideally has the same height, that is, 1 code, and width. The width is
defined as the delta between the transition points to one code and the next. The ideal code
width for an N-bit converter, where N can be 16, 12, 10, or 8, defined as 1 LSB, is:
LSB
Equation 3. Ideal code width for an N-bit converter
There is an inherent quantization error due to the digitization of the result. For 8-bit, 10-
bit, or 12-bit conversions, the code transitions when the voltage is at the midpoint
between the points where the straight line transfer function is exactly represented by the
actual transfer function. Therefore, the quantization error will be ± 1/2 LSB in 8-bit, 10-
bit, or 12-bit modes. As a consequence, however, the code width of the first (0x000)
conversion is only 1/2 LSB and the code width of the last (0xFF or 0x3FF) is 1.5 LSB.
Chapter 34 Analog-to-Digital Converter (ADC)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors
813
Содержание K22F series
Страница 2: ...K22F Sub Family Reference Manual Rev 4 08 2016 2 NXP Semiconductors...
Страница 150: ...Private Peripheral Bus PPB memory map K22F Sub Family Reference Manual Rev 4 08 2016 150 NXP Semiconductors...
Страница 168: ...Module clocks K22F Sub Family Reference Manual Rev 4 08 2016 168 NXP Semiconductors...
Страница 198: ...Security Interactions with other Modules K22F Sub Family Reference Manual Rev 4 08 2016 198 NXP Semiconductors...
Страница 258: ...Functional description K22F Sub Family Reference Manual Rev 4 08 2016 258 NXP Semiconductors...
Страница 292: ...Functional description K22F Sub Family Reference Manual Rev 4 08 2016 292 NXP Semiconductors...
Страница 398: ...Functional description K22F Sub Family Reference Manual Rev 4 08 2016 398 NXP Semiconductors...
Страница 628: ...Initialization and application information K22F Sub Family Reference Manual Rev 4 08 2016 628 NXP Semiconductors...
Страница 740: ...Initialization Application Information K22F Sub Family Reference Manual Rev 4 08 2016 740 NXP Semiconductors...
Страница 750: ...Functional description K22F Sub Family Reference Manual Rev 4 08 2016 750 NXP Semiconductors...
Страница 816: ...Application information K22F Sub Family Reference Manual Rev 4 08 2016 816 NXP Semiconductors...
Страница 866: ...Initialization Application Information K22F Sub Family Reference Manual Rev 4 08 2016 866 NXP Semiconductors...
Страница 890: ...Application information K22F Sub Family Reference Manual Rev 4 08 2016 890 NXP Semiconductors...
Страница 1028: ...Initialization Procedure K22F Sub Family Reference Manual Rev 4 08 2016 1028 NXP Semiconductors...
Страница 1040: ...Example configuration for chained timers K22F Sub Family Reference Manual Rev 4 08 2016 1040 NXP Semiconductors...
Страница 1118: ...Device mode IRC48 operation K22F Sub Family Reference Manual Rev 4 08 2016 1118 NXP Semiconductors...
Страница 1122: ...USB Voltage Regulator Module Signal Descriptions K22F Sub Family Reference Manual Rev 4 08 2016 1122 NXP Semiconductors...
Страница 1180: ...Initialization application information K22F Sub Family Reference Manual Rev 4 08 2016 1180 NXP Semiconductors...
Страница 1302: ...Application information K22F Sub Family Reference Manual Rev 4 08 2016 1302 NXP Semiconductors...
Страница 1374: ...Functional description K22F Sub Family Reference Manual Rev 4 08 2016 1374 NXP Semiconductors...