ADC32RF83 datasheet(124/138 Pages) TI

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Estimator

Freeze

Correction

Disable

Correction

Data In

Data Out

Offset Corrector

INxP

INxM

Driving Amp

VOCM

RS / 2

ADC32RF80

Digital

OUTP

OUTM

ADC

JESD

204B

Interface

Digital

Ouput

Low-Pass

Filter

RTERM

Interleaving

Engine

DDC

Block

Offset

Corrector

RDC / 2

VCM

RCM

(1)

RDC/2

(2)

124

ADC32RF80, ADC32RF83

SBAS774A – MAY 2016 – REVISED DECEMBER 2016

www.ti.com

Product Folder Links: ADC32RF80 ADC32RF83

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9.1.5 Using DC Coupling in the ADC32RF8x

The ADC32RF8x can be used in dc-coupling applications. However, the following points must be considered

when designing the system:

1. Ensure that the correct common-mode voltage is used at the ADC analog inputs.

The analog inputs are internally self-biased to VCM through approximately a 33-Ω resistor. The internal

biasing resistors also function as a termination resistor. However, if a different termination is required, the

external resistor RTERM can be differentially placed between the analog inputs, as shown in Figure 257. The

amplifier VOCM pin is recommended to be driven from the CM pin of the ADC to help the amplifier output

common-mode voltage track the required common-mode voltage of the ADC.

(1)

Set the INCR CM IMPEDANCE bit to increase the RCM from 0 Ω to > 5000 Ω.

(2)

RDC is approximately 65 Ω.

Figure 257. The ADC32RF8x in a DC-Coupling Application

2. Ensure that the correct SPI settings are written to the ADC.

As shown in Figure 258, the ADC32RF8x has a digital block that estimates and corrects the offset mismatch

among four interleaving ADC cores for a given channel.

Figure 258. Offset Corrector in the ADC32RF8x

The offset corrector block nullifies dc, fS / 8, fS / 4, 3 fS / 8, and fS / 2. The resulting spectrum becomes free

from static spurs at these frequencies. The corrector continuously processes the data coming from the

interleaving ADC cores and cannot distinguish if the tone at these frequencies is part of signal or if the tone

originated from a mismatch among the interleaving ADC cores. Thus, in applications where the signal is

present at these frequencies, the offset corrector block can be bypassed.

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