LT6202_15 datasheet(21/28 Pages) LINER

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LT6202/LT6203/LT6204

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TYPICAL APPLICATIONS

Single-Supply 16-Bit ADC Driver

Figure 5 shows the LT6203 driving an LTC1864 unipolar

16-bit A/D converter. The bottom half of the LT6203 is

in a gain-of-one configuration and buffers the 0V nega-

tive full-scale signal VLOW into the negative input of the

LTC1864. The top half of the LT6203 is in a gain-of-ten

configuration referenced to the buffered voltage VLOW and

drives the positive input of the LTC1864. The input range

of the LTC1864 is 0V to 5V, but for best results the input

range of VIN should be from VLOW (about 0.4V) to about

0.82V. Figure 6 shows an FFT obtained with a 10.1318kHz

coherent input waveform, from 8192 samples with no

windowing or averaging. Spurious free dynamic range is

seen to be about 100dB.

Although the LTC1864 has a sample rate far below the

gain bandwidth of the LT6203, using this amplifier is not

necessarilyacaseofoverkill.Thedesignerisremindedthat

A/D converters have sample apertures that are vanishingly

small (ideally, infinitesimally small) and make demands on

the upstream circuitry far in excess of what is implied by

theinnocent-lookingsamplerate.Inaddition,whenanA/D

converter takes a sample, it applies a small capacitor to

its inputs with a fair amount of glitch energy and expects

the voltage on the capacitor to settle to the true value very

quickly. Finally, the LTC1864 has a 20MHz analog input

bandwidthandcanbeusedinundersamplingapplications,

again requiring a source bandwidth higher than Nyquist.

–

LTC1864

16-BIT

250ksps

SERIAL

DATA

OUT

470pF

100

110

VIN = 0.6VDC

±200mVAC

VLOW = 0.4VDC

1/2 LT6203

LT6202/03/04 F05

Figure 5. Single-Supply 16-Bit ADC Driver

FREQUENCY (kHz)

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

–130

–140

–150

37.5

62.5

100

LT6202/03/04 F06

12.5 25

75 82.5

112.5 125

fS = 250ksps

fIN = 10.131836kHz

Figure 6. FFT Showing 100dB SFDR

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