12
Virtex-6 FPGA System Monitor
UG370 (v1.1) June 14, 2010
Analog-to-Digital Converter
The System Monitor ADC has six dedicated pins (see
). Two of these pins provide
a dedicated high-bandwidth, differential analog-input channel (V
P
, V
N
). Another two
pins are used to access an external reference voltage (V
REFP
, V
REFN
). By using an external
reference device, a reference voltage with a low-temperature coefficient (< 50 ppm/°C) can
be supplied. This voltage is used to provide stable and accurate measurements over a wide
temperature range. An internal reference circuit can also be selected by connecting V
REFN
and V
REFP
to analog ground (AGND). This internal reference is typically less accurate over
a wide temperature range than an external reference. Performance using the internal
reference circuit is specified in the
Virtex-6 FPGA Data Sheet
. For the most accurate
measurements, an external reference IC is recommended.
The remaining analog pins (AV
DD
and AV
SS
) are used to decouple the power supply for
the ADC analog circuits and provide a local AGND return for the ADC circuitry. The
System Monitor connection diagrams (using the on-chip and external reference) are shown
in
. For a more detailed discussion of required power supply connections and PC
Board layout, see
Application Guidelines, page 45
In addition to on-chip sensors, the ADC is used to digitize external analog signals. There is
one dedicated analog-input pin pair and 16 user-programmable analog-input pairs
supplied for this purpose. The ADC has a true differential-sampling analog-input scheme,
allowing the ADC to achieve a high degree of accuracy when digitizing both on-chip and
external channels.
The ADC accommodates both unipolar and bipolar analog input signals (see
). The analog-input mode is selected by writing to the System Monitor
configuration registers (see
). In Single
Channel mode, the configuration registers are also used to select the sampling modes of
the ADC and the analog input channels such as, on-chip sensors and external analog-input
channels.
Temperature Sensor
System Monitor contains a temperature sensor that produces a voltage output that is
proportional to the die temperature.
shows the output voltage of the temperature sensor.
X-Ref Target - Figure 4
Figure 4:
System Monitor Dedicated Pins
ADC
1.25V
±
0.2%
50 ppm/
°
C
2.5V – 5V
AV
DD
AV
SS
V
REFP
V
P
V
N
V
REFN
V
CCAUX
(2.5V
±
5%)
V
CCAUX
(2.5V
±
5%)
UG370_04_
061009
External Reference
ADC
AV
DD
AV
SS
V
REFP
V
P
V
N
V
REFN
On-Chip Reference
GND
Ferrite for HF noise isolation
10nF
10nF
GND
Ferrite for HF noise isolation
Package Pins
10nF
www.BDTIC.com/XILINX