Question asked by coyoo on Jan 5, 2017
Latest reply on Jan 10, 2017 by JinoL
Branched from an earlier discussion

Hi Doug,

There are several questions need you help.

1. There are two blocks between ADA4930 and AD9633, which need me to make choice: one is the mach resistor, the DEV kit used 24 ohm, our previous board used 50 ohm, there is no match resistor in figure 60 of ADA4930 datasheet, however 33ohm in figure 59; aonther is the RLC filter, is this necessary for my application? And  will the inductance destroy the DC coupling fucntion?

2. The input common-mode voltage range should be 0.3~2.8V. But, i found this parameter has different range in Chinese version datasheet, where is 0.3~1.2V. Also, there is same issue about output voltage range.

3. The DEV kit schamatic of the ADA4930 is same as figure 55 of the datasheet, so the ADA4930 was configured as G=1 and input 2Vpp, output also 2Vpp. My system, the front signal is 1Vpp, so i should refer to figure 60, am i right? Which convert the input 1Vpp to differential 2Vpp.

4, In dev kit, use Rcm(1.82K) pull-up to +3.3V. There also have several pull-down resistors. Can i remove these pull-down resistor in my design?

5. Can you teach me how to calculate each node's voltage based on figure 60 of ADA4930 datasheet? For, datasheet said "For a common-mode voltage of 1 V, each ADA4930-2 output swings between 0.501 V and 1.498 V, providing a 1.994 V p-p differential output. " I can understand how to get 1994 V p-p, but i don't know how to get 0.501 V and 1.498 V.

6. Is the VCM pin of AD9633 a output pin? Which will provide output common voltage to ADA4930's Vocm pins. How to set VCM's output voltage value? Does VCM's value equal to VREF's value? Vref=1V.