THS1401_07 Datasheet, PDF (17/26 Pages) Texas Instruments – 14-Bit, 1/3/8 MSPS, DSP-COMPATIBLE ANALOG-TO-DIGITAL CONVERTERS WITH INTERNAL REFERENCE AND PGA

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THS1401
THS1403
THS1408
SLAS248D − DECEMBER 1999 − REVISED SEPTEMBER 2005
The resistors and capacitors on the inputs decouple the driving source output from the ADC input and also serve
as first order low pass filters to attenuate out of band noise.
The input range on both inputs is 0 V to AV_DD. The full-scale value is determined by the voltage reference. The
positive full-scale output is reached, if ∆IN equals ∆REF, the negative full-scale output is reached, if ∆IN equals
−∆REF.
∆IN [V]
OUTPUT
−∆REF
− full scale
0
0
∆REF
+ full scale
APPLICATION INFORMATION
transformer coupled single-ended to differential configuration
If the application requires the best SNR, SFDR, and THD performance, the input should be transformer
coupled.
The signal amplitude on both inputs of the ADC is one half as high as in a single-ended configuration thus
increasing the ADC ac performance.
22 Ω
R
22 Ω
100 pF ^IN+
THS1401/3/8
100 pF
IN− _CML
+
1 µF
0.1 µF
Figure 20. Transformer Coupled
The following table shows the input voltages for negative full-scale output, zero output, and positive full-scale
output:
IN [VPEAK]
−∆REF
OUTPUT [PEAK]
− full scale†
0
∆REF
† _{n = 1 (winding ratio)}
0
+ full scale†
The resistor R of the transformer coupled input configuration must be set to match the signal source impedance
R = n² Rs, where Rs is the source impedance and n is the transformer winding ratio.
APPLICATION INFORMATION
single-ended configuration
In this configuration, the input signal is level shifted by ∆REF/2.
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