Please teach the following two points.
AD9681 has 2 Vcm pin.
Why are there two VCM?
How should I use it?
If VCM is one pin, I understood it.
Please teach the drive current of VCM pin.
AD9681 has two "banks" of ADCs, with four ADCs in each bank.
AD9681 Analog inputs in BANK1VIN±A1, VIN±B1,VIN±C1, VIN±D1
AD9681Analog inputs in BANK2VIN±A2, VIN±B2,VIN±C2, VIN±D2
In general we would supply the input common mode voltage for the inputs in BANK1 with VCM1, and supply the input common mode voltage for the inputs in BANK2 with VCM2. An example of this can be found on the AD9681 evaluation board. You can find the schematics at http://www.analog.com/static/imported-files/eval_boards/AD9681_Design_Integration_Files.zip .
Figure 40 in the datasheet gives an indication of the drive strength of VCM1 and VCM2. Even though Figure 40 is for VREF, the drive capability of VCM1 and VCM2 is very similar to VREF.
Thank you for considering the AD9681.
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