AD9633
Recommended for New Designs
The AD9633 is a quad, 12-bit, 80 MSPS/105 MSPS/125 MSPS analog-to-digital converter (ADC) with an on-chip sample-and-hold circuit designed for low cost...
Datasheet
AD9633 on Analog.com
ADA4930-2
Recommended for New Designs
The ADA4930-1/ADA4930-2 are very low noise, low distortion, high speed differential amplifiers. They are an ideal choice for driving 1.8 V high performance...
Datasheet
ADA4930-2 on Analog.com
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.
Thanks in advance.
Hi Doug,
If VCM has fixed 900mV output, it seems 1.8V ADI ADCs VCM would have fixed 900mV output. So AD9255 should also has its VCM outputing fixed 900mV. However, why ADA4930's datasheed says:"The VOCM pin is connected to the VCM output of the AD9255 and sets the output common mode of the ADA4930-1 at 1 V."?
BTW,
1. Did you creat different post for other questions?
2. I drawn the schematic for my application. Can you find some time to help checking it? I attached it here. I drawn it by refering figure 60 of ADA4930 datasheet. Sof if the VCM is 900mV, i must re-calculate and modify all impedence resistor's value, for figure 60 of ADA4930 datasheet based on 1000mV common mode voltage.
3.SENSE connects GND will make AD9633 selecting internal 1V reference. How to understand "INT 1V SPAN 3-4" and "INT 2V SPAN 3-5"? I think 3-5 means SENSE connects to GND, then select internal 1V VREF and result differential span at 2V. 3-4 will make ADC selecting internal 1V VREF and result differential span at 1V. Am i right?
