How to drive AD9637 use 3 pcs ADA4937-2? What's the connnection about the 6 Vocm pins of 3 pcs ADA4937-2 to the Vcm pin of AD9637? Thanks!
Thank you for your interest in the AD9637.
According to the ADA4937 datasheet, the input resistance of the VOCM pin is about 10kOhms. Six of these in parallel would be about 1.67kOhms. Assuming 1.67kOhms to ground, the AD9637 VCM pin would be driving about 0.9V/1.67kOhms = 540uA.
The AD9637 VCM buffer has no problem driving 540uA. Based on this you can drive all six ADA4937 VOCM pins with one AD9637 VCM pin. Remember to place a 0.1uF bypass capacitor to ground close to the AD9637 VCM pin.