Analog Interface
5
SBAU268 – July 2016
Copyright © 2016, Texas Instruments Incorporated
ADS8910BEVM-PDK
2
Analog Interface
As an analog interface, the evaluation board uses operational amplifiers in a variety of configurations to
drive the ADS8910B input signal and reference inputs. This section covers driver details including jumper
configuration for different input signal common modes and board connectors for a differential signal
source.
2.1
Connectors for Differential Signal Source
The ADS8910BEVM is designed for easy interfacing to an external analog differential source via a
subminiature version A (SMA) connector or 100-mil headers. J7 and J3 are SMA connectors that allow
analog source connectivity through coaxial cables. Also, 100-mil jumper cables or mini-grabbers can be
used to connect analog sources to the J4:2 and J6:2 pins.
NOTE:
The input does not support single-ended signals. The external source must be differential or
balanced keeping the negative and positive inputs to the board symmetric such that Vs(+) =
–Vs(–) at any given time.
Table 1. J7 and J3 SMA Connectors Description
Pin Number
Signal
Description
J3
Vs(–)
Negative differential board input,
1-k
Ω
input impedance
J7
Vs(+)
Positive differential board input,
1-k
Ω
input impedance
Table 2. J4 and J6 Headers Description
Pin Number
Signal
Description
J4:3
TEST 0.23 V
Do not use: diagnostic use only
J4:2
Vs(–)
Negative differential board input,
1-k
Ω
input impedance
J4:1
AGND
Analog ground
J6:3
AGND
Analog ground
J6:2
Vs(+)
Positive differential board input,
1-k
Ω
input impedance
J6:1
TEST 4.77 V
Do not use: diagnostic use only
2.2
ADC Differential Input Signal Driver
The differential signal inputs of the ADS8910B are not dynamically high impedance. SAR ADC inputs
terminate in switched-capacitor networks that create large instantaneous current loads when the switches
are closed that effectively make the ADC inputs dynamically low impedance. Thus, the evaluation board
has low impedance on board drivers that maintain ADC performance with maximum loading at the full
device throughput of 1-MSPS for signal.
