Texas Instruments ADS9110EVM-PDK, Руководство пользователя, Страница: 6 / 37

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2.2.1 Input Signal Path
Figure 1 shows the signal path for the differential signal applied at the board inputs. The board input
impedance is 1-k Ω with 10-nF differential filtering that keeps noise in external cabling common. The
overall signal path bandwidth is limited to 160-kHz by the anti-aliasing filter formed from 1-k Ω resistor and
1-nF capacitor at the amplifier feedback. Finally, the two OPA625 operational amplifiers drive the
ADS9110 differential inputs with 2.2-
Ω impedance up to 7-MHz that properly drives the low dynamic
impedance of the ADC inputs at 2 MSPS.
Figure 1. OPA625 Differential Input Driving Path
2.2.2 Input Common Mode Jumper Configuration
The ADS9110EVM board accommodates three external source common mode options: 0 V, 2.25 V, and
floating with jumpers J1 and J2 as shown in
Figure 2 .
J2 selects the OPA625 common mode as 2.25 V(J2:OPEN) or 1.25 V(J2:CLOSED). J1 increases the
OPA625 common mode by almost 100 mV to avoid amplifier output saturation with full-scale external
source signal amplitude. R
1
is installed as 280 k Ω , allowing full-scale external source signals for external
source impedance (R
S
) between 0 Ω and 32 Ω , with 0-V common mode. R
1
must be changed to
compensate for larger external source impedance (R
S
) values or for 2.25-V external source common mode
as explained in Section 2.2.3 .
6 ADS9110EVM-PDK SBAU249 – October 2015
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