LT6236 datasheet(24/50 Pages) LINER

24 / 50 page

LTC2372-16

237216f

For more information www.linear.com/LTC2372-16

betweenMUXOUT+/–andADCIN+/–asshowninFigure10a

provides the SNR benefits of the fully differential range

without sacrificing additional MUX inputs to do so. Using

the MUX configurations where CH0 to CH7 is output to

MUXOUT+ and COM to MUXOUT– enables eight single-

ended inputs to be converted with the fully differential

input range. The COM MUX input channel is used in the

feedback connection of the buffer amplifier connected

in a follower configuration to improve the distortion

performance of the circuit. THD degradation would oth-

erwise occur due to the non-linear voltage drop across

the MUX switch from the input current of the buffer and

the non-linear on-resistance of the MUX switch. The 1k

resistor between COM and MUXOUT– maintains negative

feedback around the buffer when the MUX turns OFF, so

that the buffer output does not rail. Eight single-ended

inputs achieve an SNR of 96dB with this circuit as shown

in Figure 10b, which is a 2.5dB improvement in SNR over

single-ended operation.

applicaTions inForMaTion

Figure 10a. LT6236 Buffering a Single-Ended 0V to 4.096V Input Signal and the LT6237 Configured to Perform a

Single-Ended to Differential Conversion to the ±4.096V Fully Differential Input Range

Figure 10b. 32k Point FFT fSMPL = 500ksps,

fIN = 1kHz for Circuit Shown in Figure 10a

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

COM

MUX CHANNELS

CH0 AND COM

SELECTED

MUXOUT–

ADCIN–

MUXOUT+

ADCIN+

LTC2372-16

16-BIT ADC CORE

–

237216 F10a

1200pF

VCM = 2.048V

LT6237

–

100pF

4.096V

LT6236

V+

V–

V+

V–

499

+–

24.9

2700pF

24.9

SNR = 96dB

THD = –105.1dB

SINAD = 95.6dB

SFDR = 105.6dB

FREQUENCY (kHz)

100

150

200

250

–180

–160

–140

–120

–100

–80

–60

–40

–20

237216 F10b

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