RHF1401_12 Datasheet, PDF (27/42 Pages) STMicroelectronics – Rad-hard 14-bit 30 Msps A/D converter

RHF1401
User manual
3.2
3.2.1
Driving the analog input
The input frequency can range from DC to tens of MHz.
The input stages (VIN and VINB) have a special design that limits the input amplitude. For
each of them, the maximum input voltage is about 1.6 V for low sampling frequencies and
less for high sampling frequencies. Low voltage is ground.
Consequently, the maximum input voltage read by the ADC for Single-ended mode is 1.6 V
regardless of the VREFP and VREFM voltages.
Differential mode
The INCM value must be equal to the medium input voltage value.
In differential mode, high sampling limitation is seen in Figure 25.
For all input frequencies, it is mandatory to add a capacitor on the PCB (between VIN and
VINB) to cut the HF noise. The lower the frequency, the higher the capacitor.
The full-scale range is twice the difference between Vrep and Vrefm.
Figure 52. Equivalent VIN - VINB (differential input)
VIN -VINB
VIN
FS (full-scale)
= 2(VREFP - VREFM)
(level + FS, code 16383)
INCM (level 0, code 8191)
VINB
(level - FS, code 0)
Table 12. Differential mode output codes
Vin - Vinb =
DFSB = 1
+ (VREFP-VREFM)
3FFF
0
1FFF
- (VREFP-VREFM)
0000
AM04567
DFSB = 0
1FFF
3FFF
2000
The RHF1401 is designed to obtain optimum performance when driven on differential inputs
with a differential amplitude of two volts peak-to-peak (2 V_pp). This is the result of 1 V_pp on
the VIN and VINB inputs in phase opposition.
The RHF1401 is specifically designed to meet sampling requirements for intermediate
frequency (IF) input signals. In particular, the track-and-hold in the first stage of the pipeline
is designed to minimize the linearity limitations as the analog frequency increases.
Doc ID 13317 Rev 8
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