RHF1401_12 Datasheet, PDF (25/42 Pages) STMicroelectronics – Rad-hard 14-bit 30 Msps A/D converter

RHF1401
3
User manual
User manual
3.1
Optimizing the power consumption
The polarization current in the input stage is set by an external resistor (R_pol). When
selecting the resistor value, it is possible to optimize the power consumption according to
the sampling frequency of the application. For this purpose, an external R_pol resistor is
placed between the IPOL pin and the analog ground.
The values in Figure 50 are achieved with VREFP = 1 V, VREFM = 0 V, INCM = 0.5 V and
the input signal is 2 Vpp with a differential DC connection. If the conditions are changed, the
Rpol resistor varies slightly.
Figure 50 shows the optimum Rpol resistor value to obtain the best ENOB value. It also
shows the minimum and maximum values to get good results. ENOB decreases by
approximately 0.2 dB when you change Rpol from optimum to maximum or minimum.
If Rpol is higher than the maximum value, there is not enough polarization current in the
analog stage to obtain good results. If Rpol is below the minimum, THD increases
significantly.
Therefore, the total dissipation can be adjusted across the entire sampling range to fulfill the
requirements of applications where power saving is critical.
For sampling frequencies below 2 MHz, the optimum resistor value is approximately
400 kOhms.
Figure 50. Rpol values vs. F_s
1000
ma x imum
optimum
minimum
100
10
1
0
5
10
15
20
25
30
35
40
S ampling frequency (Ms ps )
The power consumption depends on the Rpol value and the sampling frequency. In
Figure 51, it is shown with the internal references disabled (REFMODE = 1) and Rpol
defined in Figure 50 as the optimum.
Doc ID 13317 Rev 8
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