ISLA224S
16
FN7911.2
April 25, 2013
User Initiated Reset
Recalibration of the ADC can be initiated at any time by driving
the RESETN pin low for a minimum of one clock cycle. An
open-drain driver with a drive strength in its high impedance
state of less than 0.5mA is recommended, as RESETN has an
internal high impedance pull-up to OVDD. As is the case during
power-on reset, RESETN and DNC pins must be in the proper
state for the calibration to successfully execute.
The performance of the ISLA224S changes with variations in
temperature, supply voltage or sample rate. The extent of these
changes may necessitate recalibration, depending on system
performance requirements. Best performance will be achieved
by recalibrating the ADC under the environmental conditions at
which it will operate.
A supply voltage variation of <100mV will generally result in an
SNR change of <0.5dBFS and SFDR change of <3dBc. In
situations where the sample rate is not constant, best results will
be obtained if the device is calibrated at the highest sample rate.
Reducing the sample rate by less than 80MSPS will typically
result in an SNR change of <0.5dBFS and an SFDR change of
<3dBc.
Figures
36 through
41 show the affect of temperature on SNR
and SFDR performance with power on calibration performed at
-40°C, +25°C, and +85°C. Each plot shows the variation of
SNR/SFDR across temperature after a single power on
calibration at -40°C, +25°C and +85°C. Best performance is
typically achieved by a user-initiated power on calibration at the
operating conditions, as stated earlier. However, it can be seen
that performance drift with temperature is not a very strong
function of the temperature at which the power on calibration is
performed.
FIGURE 34. ADC CORE BLOCK DIAGRAM
DIGITAL
ERROR
CORRECTION
SHA
1.25V
INP
INN
CLOCK
GENERATION
2.5- BIT
FLASH
6- STAGE
1.5- BIT/ STAGE
3- STAGE
1-BIT/ STAGE
3- BIT
FLASH
+
–
FLASH
2.5-BIT
FIGURE 35. CALIBRATION TIMING
CLKP
CLKN
CALIBRATION
BEGINS
CALIBRATION
COMPLETE
CALIBRATION
TIME
RESETN
CAL_STATUS
BIT