BL4S200 User’s Manual
40
3.4 A/D Converter Inputs
The single A/D converter chip used in the BL4S200 has a resolution of 12 bits (11 bits for
the value and one bit for the polarity). The A/D converter chip has a programmable ampli-
fier. Each external input has circuitry that provides scaling and filtering. All 8 external
inputs are scaled and filtered to provide the user with an input impedance of 1 M
and a
variety of single-ended unipolar, single-ended bipolar, and differential bipolar ranges as
shown in Table 8.
Figure 15 shows a pair of A/D converter input circuits. The resistors form an approx. 10:1
attenuator, and the capacitors filter noise pulses from the A/D converter inputs.
Figure 15. Buffered A/D Converter Inputs
The A/D converter chip can only accept positive voltages. By pairing the analog inputs and
setting the reference voltage from the D/A converter, single-ended unipolar, single-ended
bipolar, differential bipolar, or current (4–20 mA on channels 0–3 only) measurements are
possible, and can be configured for each channel or channel pair with the
opmode
parame-
ter in the
anaInConfig()
software function call. Adjacent A/D converter inputs AIN4–
AIN7are paired to make bipolar measurements. The available voltage ranges are listed in
Table 8.
ADC
953 k
W
10 pF
AIN0
AGND
AIN1
10 pF
Ref. Voltage
from D/A Converter
105 k
W
105 k
W
953 k
W
