RHF1401_12 Datasheet, PDF (29/42 Pages) STMicroelectronics – Rad-hard 14-bit 30 Msps A/D converter

RHF1401
User manual
3.2.2
Single-ended mode
Figure 55. Optimized single-ended configuration (DC coupling), external REFP
VIN
max = 1.6V
External
INCM
REFP
VIN
0 V (ground)
VINB
INCM REFM
Ground
VIN
External
INCM
AM04569
Table 13. Single-ended mode output codes with Vinb = INCM
Vin =
DFSB = 1
INCM + (VREFP-VREFM)
3FFF
INCM
1FFF
INCM - (VREFP-VREFM)
0000
DFSB = 0
1FFF
3FFF
2000
The RHF1401 is designed for use in a differential input configuration. Nevertheless, it can
achieve good performance in a single-ended input configuration. In single-ended,
performances depend on the input voltage, input frequency, voltage of references and
sampling frequency (refer to Figure 42. to Figure 49.)
VREFP and INCM internal voltage references are not adapted to Single-ended mode.
Some applications may require a single-ended input, which can easily be achieved with the
configuration shown in Figure 56, Figure 57 for AC coupling or Figure 35. for DC coupling.
However, with this type of configuration, a degradation in the rated performance of the
RHF1401 may occur compared with a differential configuration. A sufficiently decoupled DC
reference should be used to bias the RHF1401 inputs. An AC-coupled analog input can also
be used and the DC analog level set with a high value resistor R (6 kΩ to 100 kΩ) connected
to a proper DC source. Cin and R behave like a high-pass filter and are calculated to set the
lowest possible cut-off frequency.
Each input is limited to about 1.6 V due to the CMOS transistor on the input path. Voltage
can be a bit more or less than 1.6 V depending on temperature, AVCC, and variations from
one die to another (see Figure 3 for the analog input schematic). This “input limitation” is
independent of the VREFP and VREFM values.
Doc ID 13317 Rev 8
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