ADS6142-HT datasheet(35/49 Pages) TI1

35 / 49 page

Full−scale differential input pp + (Voltage forced on VCM)

1.33

ADS6142-HT

www.ti.com

SLWS234

– DECEMBER 2011

External Reference

When the device is in external reference mode, VCM acts as a reference input pin. The voltage forced on the

VCM pin is buffered and gained by 1.33 internally, generating the REFP and REFM voltages. The differential

input voltage corresponding to full-scale is given by Equation 1.

(1)

In this mode, the 1.5-V common-mode voltage to bias the input pins has to be generated externally. There is no

change in performance compared to internal reference mode.

COARSE GAIN AND PROGRAMMABLE FINE GAIN

The ADS6142 includes gain settings that can be used to improve SFDR performance (compared to 0 dB gain

mode). The gain settings are 3.5 dB coarse gain and 0 dB to 6 dB programmable fine gain. For each gain

setting, the analog input full-scale range scales proportionally, as shown in Table 15.

The coarse gain is a fixed setting of 3.5 dB and is designed to improve SFDR with little degradation in SNR. The

fine gain is programmable in 1 dB steps from 0 dB to 6 dB. With fine gain, SFDR improvement is also achieved,

but at the expense of SNR (there is about 1 dB SNR degradation for every 1 dB of fine gain).

So, the fine gain can be used to trade-off between SFDR and SNR. The coarse gain makes it possible to get the

best SFDR but without losing SNR significantly. At high input frequencies, the gains are especially useful as the

SFDR improvement is significant with marginal degradation in SINAD. The gains can be programmed using the

<COARSE GAIN> (see Table 7) and <FINE GAIN> (see Table 12). Note that the default gain after

reset is 0 dB.

Table 15. Full-Scale Range Across Gains

GAIN, dB

TYPE

FULL-SCALE RANGE, VPP

Default after reset

2.00

3.5

Coarse setting (fixed)

1.34

1.78

1.59

1.42

Fine gain (programmable)

1.26

1.12

1.00

Submit Documentation Feedback

Product Folder Link(s) :ADS6142-HT

ADS6142-HT Datasheet(PDF) 35 Page - Texas Instruments

ADS6142-HT Datasheet(HTML) 35 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

Datasheet Download

Link URL