RHF1401_12 Datasheet, PDF (28/42 Pages) STMicroelectronics – Rad-hard 14-bit 30 Msps A/D converter

User manual
Figure 53. 2 V_pp differential input
INCM
INCM
VIN -VINB (2 Vp-p)
RHF1401
1V
REFP
VIN
REFMODE
2.5V
VINB
INCM
REFM
0.5V
Ground
AM04570
Figure 54 shows a differential input solution. The input signal is fed to the transformer’s
primary, while the secondary drives both ADC inputs. The transformer must be matched
with generator output impedance: 50 Ω in this case for proper matching with a 50 Ω
generator. The tracks between the secondary and VIN and VINB pins must be as short as
possible.
Figure 54. Differential implementation using a balun
50 Ω track
ADT1 -1
1:1
Short track
VIN
Analog input signal
(50 Ω output)
33 pF
50 Ω
VINB
INCM
470 nF* ceramic
(as close as possible
to the transformer)
*the use of a ceramic technology is
preferable for a large bandwidth
stability of the capacitor
100 nF* ceramic
(as close as
possible to
INCM pin)
External
INCM
(optional)
AM04571
The input common-mode voltage of the ADC (INCM) is connected to the center tap of the
transformer’s secondary in order to bias the input signal around the common voltage (see
Table 7: Internal reference voltage).The INCM is decoupled to maintain a low noise level on
this node. Ceramic technology for decoupling provides good capacitor stability across a
wide bandwidth.
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Doc ID 13317 Rev 8