Hey ADI Team,
I have a question regarding the AD8330 VGA:
Based on the datasheet page 3, the full-scale input of the input interface is specified as MIN: +/-1.4V, Typ +/-2V. Then on page 21 of the datasheet in the right top corner is a basic connections diagram (Figure 57) which specifies: INPUT 0V to +/-2V MAX.
I would like to understand what the maximum input voltage is and I understand that the maximum value also depends on what the gain (Vdbs) setting is. But the datasheet mentions a "MIN = +/-1.4V", "TYP = +/-2V" and MAX = "+/-2V" on various pages.
Question 1: what is intended with the 'minimum value of +/-1.4V' for the input voltage, when page 21 specifies a MAX value of +/-2V?
Question 2: I'm currently running this device at supply voltage of 5.0V. Do any of the performance parameters change if I would lower this voltage to 3.3V, is there any adverse impact? My goal is to have the maximum performance and gain possible. For example, VMAG is specified from 0V to 5V (based on 5V supply) and VMAG shows a proportional graph between gain multiplication factor and VMAG. If the supply is limited to 3.3V, is my assumption correct that VMAG is limited to 3.3V as well and that the graph in figure 5 will basically be cut-off at 3.3V (or around a multiplication factor of 5.5 to 6)? Is noise performance impacted by changing the supply from 5V down to 3.3V?
Question 3: I selected this device based on the convenient wide gain of 0-50dB which can be 20-70dB by adjusting Vmag, but I'm concerned with the output referred noise performance (fig 19) which shows that output noise increases dramatically when increasing Vmag, up to nearly 5000nV/√Hz. In the addition, the AD8330 datasheet is referring to this device as a "Low Cost VGA". Previously I used the AD8331 which has a gain range that is not as wide and hence I had to cascade two of these amps. The AD8331 datasheet points to much improved output referred noise when compared to the AD8330, which is important for our application since we are driving a 16-bit ADC and need as much resolution as possible. Is there perhaps another option, no matter how expensive, that offers wide gain and low(er) noise than either AD8330 and AD8331?
Application:
We have a photodiode in an optical network with transimpedance amplifier (based on the ADA4817) which is driving the VGA. We need to ability for our VGA to have at least 50-55dB gain with as little noise as possible since we are driving 16 bit ADC's and we have observed significant noise in the digitized signal when increasing gain.
Thank you so much for your feedback!
Best,
Peter
