ADS5560 Datasheet, PDF (45/61 Pages) Texas Instruments – 16-BIT, 40/80 MSPS ADCs WITH DDR LVDS/CMOS OUTPUTS

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8 Application and Implementation
ADS5560, ADS5562
SLWS207B – MAY 2008 – REVISED JANUARY 2016
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
In the design of any application involving a high-speed data converter, particular attention should be paid to the
design of the analog input, the clocking solution, and careful layout of the clock and analog signals. The
ADS5562 evaluation module (EVM) is one practical example of the design of the analog input circuit and clocking
solution, as well as a practical example of good circuit board layout practices around the ADC.
8.2 Typical Application
The analog inputs of the ADS5562 device must be fully differential and biased to an appropriate common mode
voltage, VCM. End equipment typically does not have a signal that already meets the requisite amplitude and
common mode and is fully differential. Therefore, a signal conditioning circuit is required for the analog input. If
the amplitude of the input circuit is such that no gain is needed to make full use of the full-scale range of the
ADC, then a transformer coupled circuit as used on the EVM can be used with good results. The transformer
coupling is inherently low-noise, and inherently AC-coupled so that the signal may be biased to VCM after the
transformer coupling. Figure 59 shows an example of transformer coupling as used on the ADS556x EVM.
0.1 mF
0.1 mF 0.1 mF
1:1
0.1 mF
1:1
0.1 mF
39 nH
50 W
0.1 mF
25 W
0.1 mF
50 W
39 nH
25 W
ADS556x
15 W
INP
50 W
22 pF
50 W
INM
15 W
VCM
Figure 59. Drive Circuit Using RF Transformers
S0329-01
If signal gain is required, or the input bandwidth is to include the spectrum all the way down to DC such that AC
coupling is not possible, then an amplifier-based signal conditioning circuit would be required. Figure 60 shows
the LMH6552 device interfaced with the ADS5562 device. The LMH6552 device is configured to have to single-
ended input with a differential outputs follow by the first Nyquist-based low-pass filter with 40-MHz bandwidth.
Figure 60 also shows the power supply recommendations for the amplifier.
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