25

REF6125, REF6130, REF6133, REF6141, REF6145, REF6150

www.ti.com

SBOS747B – MAY 2016 – REVISED AUGUST 2016

Product Folder Links: REF6125 REF6130 REF6133 REF6141 REF6145 REF6150

Submit Documentation Feedback

Copyright © 2016, Texas Instruments Incorporated

Typical Application (continued)

10.2.2 Detailed Design Procedure

The data acquisition system shown in Figure 54 has three major contributors to the noise and accuracy in the

system: the input driver, the reference with driver, and the data converter. Each analog block is carefully

designed so that the data converter specifications limit the system specifications. The THS4551, a fully

differential operational amplifier is used to drive the 18-bit ADC (ADS8881). The charge-kickback RC filter at the

output of the THS4551 is used to reduce the charge kickback created by the opening and closing of the sampling

switch inside the ADC. Design the RC filter so that the voltage at the sampling capacitor settles to 18-bit

accuracy within the acquisition time of the ADC.

Data-acquisition systems require stable and accurate voltage references in order to perform the most accurate

data conversion. The REF61xx family of voltage references have integrated an ADC drive buffer, and can

therefore drive the REF pin of the ADS8881 directly, without the need for an external reference buffer. See the

Integrated ADC Drive Buffer section for more details about reference-buffer requirements. Correct output

capacitor selection for the REF61xx is very important in this design. The Stability section describes the ESR

requirements of the output capacitor for stability and burst-mode requirements. A capacitance of 1 μF is

connected to the FILT pin to reduce broadband noise of the REF61xx.

10.2.2.1 Results

Table 1 summarizes the measured results.

Table 1. Measured Results

SPECIFICATION

MEASURED RESULT

SNR

100.5 dB

ENOB

16.4

THD

–125.9 dB

Throughput

1 MSPS

Burst mode

First sample > 18-bit precision

Power consumption

40 mW