ADwin-Gold
USB / ENET, manual version 3.8, October 2005
13
Inputs and Outputs
ADwin
Zero offset U
OFF
In the bipolar setting you will get a zero offset, also called offset U
OFF
in the fol-
lowing text.
For the voltage range of
−
10V … +10V applies:
U
OFF
=
−
10V
Gain factor k
v
The
ADwin-Gold
has a programmable gain (PGA), with which you can amplify
the input voltage by the factors 1, 2, 4, and 8. At the same time the measure-
ment range gets smaller by the corresponding gain factor k (see Annex "Tech-
nical Data").
Please note that upon applications with k
V
>1 the interference signals are
amplified respectively.
Quantization level U
LSB
The quantization level (U
LSB
) is the smallest digitally displayable voltage differ-
ence and is equivalent to the voltage of the least significant bit (LSB). It is dif-
ferent for the two ADCs:
– 16-bit ADC: U
LSB
= 20V / 2
16
= 305.175µV
– 14-bit ADC: U
LSB
= 20V / 2
14
= 1220.7µV
The measured 16-bit value of the ADC is returned in the lower word of the
reg-
ister.
A DAC value, which is to be output, has to be available there.
Fig. 9 – Storage of the ADC/DAC bits in the memory
In order to compare the measurement values of the 14-bit ADC with the values
of the 16-bit ADC, the converted value is written left-aligned into the lower word
of the register at the 14-bit ADC. Therefore the lower 2 bits are always 0 (zero).
The 16384 digits of the 14-bit ADC are mapped to the 65536 digits of the 16-
bit ADC. Thus 4 digits of the 16-bit ADC are equivalent to one digit of the 14-
bit ADC.
Therefore the following equations can be used for both ADC types:
Conversion Digit
'
Voltage
DAC
For a DAC:
ADC
For an ADC (14-bit and 16-bit):
Bit No.
31…16
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
32-bit-
memory
0
16-bit value of the 16-bit ADC / DAC in the lower word
0
14-bit value of the 14-bit ADC in the lower word
0
0
UOUT Digits ULSB UOFF
+
⋅
=
Digits
UOUT UOFF
–
ULSB
---------------------------------------------
=
Digits
kv UIN
⋅
UOFF
–
ULSB
----------------------------------------------------
=
UIN
Digits ULSB UOFF
+
⋅
kv
---------------------------------------------------
=
