Virtex-6 FPGA System Monitor
43
UG370 (v1.1) June 14, 2010
Analog Inputs
The ADC output coding in unipolar mode is straight binary. The designed code transitions
occur at successive integer LSB values such as 1 LSB, 2 LSBs, and 3 LSBs (and so on). The
LSB size in volts is equal to 1V/2
10
or 1V/1024 = 0.977 mV. The ideal transfer function is
illustrated in
.
Bipolar Input Signals
The analog inputs can accomodate analog input signals which are positive and negative
with respect to a common mode or reference. To accomodate these types of signals, the
ADC must be operated in bipolar mode. Bipolar mode is selected by writing to
configuration register 0. All input voltages must be positive with respect to analog ground
(AV
SS
).
When bipolar operation is enabled, the differential analog input (V
P
– V
N)
can have a
maximum input range of ±0.5V. The common mode or reference voltage should not exceed
0.5V in this case (see
). At a maximum common mode voltage of 1V on V
N
the
differential analog input (V
P
– V
N
) should not exceed ±100 mV.
X-Ref Target - Figure 20
Figure 20:
Unipolar Transfer Function
Input Voltage (mV)
10-Bit Output Code (He
x)
UG370_20_060809
000
001
003
004
3FF
Output Code
Full Scale
Transition
3FE
3FD
002
1
2
3
999
Full Scale Input = 1V
1 LSB = 1V / 1024 = 977 µV
X-Ref Target - Figure 21
Figure 21:
Differential Analog-Input Range
UG370_21_060809
V
P
, V
N
Vo
lt
s
0V
0.5V
1.5V
2.5V
1V
2V
V
P
V
N
±0.5V – ±0.1V
0.5V – 1V
ADC
V
P
= ±0.5V
V
P
= ±0.1V
V
N
= 0.5V
V
N
= 1V
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