9.2.2 Detailed Design Procedure

The data acquisition system shown in Figure 9-1 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 REF60xx 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

Section 8.3.1 for more details about reference-buffer requirements. Correct output capacitor selection for

the REF60xx is very important in this design. Section 8.3.4 describes the ESR requirements of the output

capacitor for stability and burst-mode requirements. A capacitance of 1μF is connected to the FILT pin to reduce

broadband noise of the REF60xx.

9.2.2.1 Results

Table 9-1 summarizes the measured results.

Table 9-1. Measured Results

SPECIFICATION

MEASURED RESULT

SNR

100.5dB

ENOB

16.4

THD

–125.9dB

Throughput

1MSPS

Burst mode

First sample > 18-bit precision

Power consumption

40mW

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REF60

SBOS708C – MAY 2016 – REVISED APRIL 2026

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