Analog Interface; Connectors For Differential Signal Source; Adc Differential Input Signal Driver - Texas Instruments ADS8900BEVM-PDK User Manual

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Analog Interface

As an analog interface, the evaluation board uses operational amplifiers in a variety of configurations to
drive the ADS8900B 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 ADS8900BEVM 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.
Pin Number
J3
J7
Pin Number
J4:3
J4:2
J4:1
J6:3
J6:2
J6:1
2.2

ADC Differential Input Signal Driver

The differential signal inputs of the ADS8900B 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.
SBAU269 – October 2016
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Table 1. J7 and J3 SMA Connectors Description
Signal
Vs(–)
Vs(+)
Table 2. J4 and J6 Headers Description
Signal
TEST 0.23 V
Vs(–)
AGND
AGND
Vs(+)
TEST 4.77 V
Copyright © 2016, Texas Instruments Incorporated
Description
Negative differential board input,
1-kΩ input impedance
Positive differential board input,
1-kΩ input impedance
Description
Do not use: diagnostic use only
Negative differential board input,
1-kΩ input impedance
Analog ground
Analog ground
Positive differential board input,
1-kΩ input impedance
Do not use: diagnostic use only
Analog Interface
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ADS8900BEVM-PDK