ADC14X250 datasheet(45/69 Pages) TI1

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Driver

LC LPF

VCMO = VCM

VCC+

VCC-

VIN+

VIN-

VCM

ADC

0.1uF

200:

0.1uF

Driver

0.1uF

LC BPF

Vcc+

VIN+

VIN-

VCM

ADC

0.1uF

10uF

10 :

5 :

ADC14X250

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Figure 44. Bandpass Filter Anti-Aliasing Interface

DC coupling to the analog input is also possible but the input common-mode must be tightly controlled for

specified performance. The driver device must have an output common-mode that matches the input common-

mode of the ADC14X250 device and the driver must track the VCM output from the ADC14X250 device, as

shown in the example DC coupled interface of Figure 45 because the input common-mode varies with

temperature. The common-mode path from the VCM output, through the driver device, back to the ADC14X250

device input, and through a common-mode detector inside the ADC14X250 device forms a closed tracking loop

that will correct common-mode offset contributed by the driver device but the loop must be stable to ensure

correct performance. The loop requires the large, 10-µF capacitor at the VCM output to establish the dominant

pole for stability and the driver device must reliably track the VCM output voltage bias. The current drive strength

and voltage swing of the VCM output bias limits the correctable amount of common-mode offset.

Figure 45. DC Coupled Interface

9.1.1.5 Clipping

The ADC14X250 device has two regions of signal clipping: code clipping (over-range) and ESD clipping. When

the input signal amplitude exceeds the full-scale reference range, code clipping occurs during which the digital

output codes saturate. If the signal amplitude increases beyond the absolute maximum rating of the analog

inputs, ESD clipping occurs due to the activation of ESD diodes.

TI does not recommend ESD clipping and activation of the ESD diodes at the analog input, which may damage

or shorten the life of the device. This clipping may be avoided by selecting an ADC driver with an appropriate

saturating output voltage, by placing insertion loss between the driver and ADC, by limiting the maximum

amplitude earlier in the signal path at the system level, or by using a dedicated differential signal limiting device

such as back-to-back diodes. Any signal swing limiting device must be chosen carefully to prevent added

distortion to the signal.

ADC14X250 Datasheet(PDF) 45 Page - Texas Instruments

ADC14X250 Datasheet(HTML) 45 Page - Texas Instruments

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