In this three-part series, I discussed the solutions for generating two well-matched, low-drift voltage references. We started with three topologies in Part 1, we compared and contrasted the differences in terms of performance in Part 2. Now, let’s take a look at other design considerations of these solutions: space consumption and cost.
Space Consumption and Cost
Apart from system performance, PCB real estate requirements can be crucial in high-density applications. A glance at the total PCB space (no decoupling capacitors are considered) for each solution is given as Figure 1.
Table 1 below shows a brief calculation of the space needed (only body dimension is considered). By offering dual outputs from one integrated solution with a package size of 4.64 mm2, the REF2030 reduces total space by 83% and 67% relative to that occupied by Solution 1 and Solution 2, respectively. From the cost point of view, the REF2030 is only $1.4, which is 52% lower than Solution 1 and 30% lower than Solution 2.
Table 1: Space Consumption and Cost
Conclusion
Solution 1
Built by two independent voltage references, Solution 1 is quite straightforward and easy to implement. However, the drawback is also obvious: it is limited to availability in voltage options and has no direct drift tracking between outputs. Besides, using two low-drift high-precision references is quite pricy.
Solution 2
While consuming more components and board space, Solution 2 costs less and has better drift tracking than Solution 1. However, the accuracy of VBIAS in Solution 2 is worse than Solution 1 because it depends on the drift of VREF, voltage divider and buffer amplifier. On the plus side, Solution 2 is flexible in designing different bias voltages, where VBIAS ≠ VREF/2.
Solution 3
The most notable difference of Solution 3 is the one-chip solution. This design has best initial accuracy, lower cost, and smaller PCB space usage. In fact, Solution 3 has 90% better output matching, consumes 67% smaller space and costs 30% less than Solution 2. In another words, if you are targeting at a low-drift system, and you don’t want to pay high price for precision performance, Solution 3 (REF2030) could be a good option.
Table 2: Final Comparison
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