Virtex-6 FPGA System Monitor
33
UG370 (v1.1) June 14, 2010
System Monitor Timing
The remaining error (deviation from the dashed black line) is caused by gain error or
incorrect slope (m). This error is corrected by multiplying the ADC output code by a
correction factor.
Note:
Digital calibration can result in some loss of the analog input range at the start and end of the
ADC input range. This is illustrated in
where the ADC output never reaches 3FFh. Typically,
the loss of input range is no more than 20 mV at either end of the transfer function. For most
monitoring applications, the loss is insignificant.
System Monitor Timing
All System Monitor timing is synchronized to the DCLK. The ADCCLK is equal to DCLK
divided by the user selection in configuration register 2 (see
). The
ADCCLK is an internal clock used by the ADC and is
not
available externally. ADCCLK is
only included here to aid in describing the timing.
The ADC block in System Monitor is operated in one of two possible timing modes,
continuous-sampling mode and event-driven sampling mode.
•
In continuous-sampling mode, the ADC automatically starts a new conversion at the
end of a current conversion cycle.
•
In event-sampling mode, the user must initiate the next conversion after the current
conversion cycle ends, by using the CONVST or CONVSTCLK inputs.
The operating mode is selected by writing to configuration registers 0 (see
). A detailed timing diagram for System Monitor is shown
in
describes the timing parameters. Reference the
Virtex-6 FPGA Data Sheet
for the latest System Monitor timing specifications. The robust
nature of the System Monitor ensures continued and correct operation even if the external
clock input DCLK is stopped. In this situation, the System Monitor automatically switches
X-Ref Target - Figure 13
Figure 13:
Offset and Gain Correction
Ideal ADC
Offset and
Gain Removed
Offset
Error
Actual
Po
sitiv
e Gain Error
Offset
Removed
ADC Code
Input Voltage (V
IN
)
Code = (Gain x V
IN
) + Offset
y = m.x + c
3FFh
1V
UG370_13_060809
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