ST ST7 - Page 123

123/317
5-Peripherals
This will yield two results, Adc0 and Adc1. If we take the sum of these values, whatever the
value of V, it will range from 0 + 0 = 0 to 255 + 255 = 510. This new result now has a resolution
of 511 points, which is almost double the original resolution.
The figure below depicts this.
05-adc3
V0
Vdda
255 2×
------------------+
ADC
adcdr
Vin
Analog
input
Vana
Extra step = analog voltage
equivalent to 1/2 lsb
(V
DDA
/ 510)
1
2
adc0
adc0+1
V0
V1
Vana
min
V1 = V0 + ∆V
with
∆V= V
DDA
/255
and
extra step =
∆
V/2
V0
≤
Vana < (V0 +
∆
V/2)
adc0
adc0+1
V0
V1
Vana
min
(V0 + ∆V/2) ≤ Vana < V1
Vin acquisition
without extra step:
Vin = Vana
adc0 adc0
Vin acquisition
with extra step:
Vin = Vana +∆V/2
adc0
adc0 + 1
9bitsaccuracy
Result:
2adc0
2adc0 + 1
Vin Vin
Conversion
Conversion
+
=
Example of a simplest scheme using an extra step
signal to double the accuracy
2 acquisitions:
1°) acquisition of Vana
2°) acquisition of Vana + extra step