u-blox LEON-G100 ECALL, Руководство по системной интеграции

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LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3 Preliminary System description
Page 72 of 125
Calibration is performed providing two known reference values (V_1 and V_2) instead of the voltage source
(V_S) that has to be measured by the ADC.
V_1 and V_2 values should be as different as possible: taking into account of the ADC applicable range, the
maximum limit and the minimum limit for the voltage source has to be applied to obtain the best accuracy in
calibration.
The following values are involved in the calibration procedure:

V_1: the first (e.g. maximum) reference known voltage in mV applied in the calibration procedure

V_2: the second (e.g. minimum) applied reference known voltage in mV applied in the calibration procedure

ADC_1: the AT+UADC=0 response when V_1 is applied

ADC_2: the AT+UADC=0 response when V_2 is applied
This is the procedure to calibrate the ADC:
1.
Apply V_1
2. Read ADC_1
3. Apply V_2
4. Read ADC_2
5. Evaluate GAIN value with the following formula:
) 2 _ ADC 1 _ ADC (
) 2 _ V 1 _ V (
* 16384 = GAIN
-
-
6.
Evaluate OFFSET value with the following formula:
GAIN
8192
+
) 2 _ V 1 _ V (
) ADC_2 * V_1 ADC_1 * V_2 (
= OFFSET
-
-
Now the voltage source (V_S) value expressed in mV can be exactly evaluated from the AT+UADC=0 response
(ADC_VALUE) when V_S is applied, with the following formula:
16384
8192 - GAIN * ) + _ A (
= _
OFFSET VALUE DC
S V
where the parameters are defined as following:

V_S is the voltage source value expressed in mV

ADC_VALUE is the AT+UADC=0 response when V_S is applied

GAIN is calculated in the calibration procedure (see point 5)

OFFSET is calculated in the calibration procedure (see point 6)