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MSP430L092 Introduction Slide 11
With the previous slide, the Analog Pool has been grayed out so that the comparator may be focused on. Now, there are three main pieces to cover about the comparator. These are the input structure, the compensation, and the post-comparator filter. The Analog Pool is working in what TI calls a 256 mV domain.  Remember from the previous slide that the internal reference, the low voltage references, and the 256 mV reference provide the DAC a range of 1 to 256 mV. In contrast, the IO domain of the L092 is about 2 V, so the question is how does TI bring together these two different voltage domains? There is an input resistor network, and this is what is used to bridge the domains. The important piece to remember in all of this is that it is the user’s responsibility to make sure that both the IO requirements of the L092 are met in addition to the input requirements of the comparator. The next piece is the compensation within the comparator structure itself. In legacy MSP430 systems, users will need to actually perform multiple measurements, switching the inputs to account for errors, while the comparator in the L092 provides an auto zeroing function to compensate for any voltage offset. Just a quick note, here the presentation will address the offset error indicated in red. The other overdrive error indicated in purple will be addressed in a later slide.  It is important to note that this feature does come at a cost. When users enable the compensation mechanism that adds two clock cycles to the comparator output response. The third and final piece of the comparator that TI would like to highlight is the post-comparator filter. There is a difference between how this comparator is used in legacy MSP430 comparators in that with legacy devices, users would typically find an RC filter. This prevents the output from switching or, what is called, glitching when the voltages of the comparator inputs are right at or near the same level causing the output to simply glitch between 0 and 1 with noise. With the L092, instead of using a filter, the L092 uses a voting logic to determine the output state. This is a nice feature to have in slow-moving signals that spend a lot of time or hang out at the threshold crossing. The comparator and the DAC can be used either individually or integrated to create an ADC, which will be discussed next.
PTM Published on: 2011-04-08