Teoria: Il concetto di capacità commutata (dalla ML)

Switched Cap Blocks
Switched cap blocks start out with the same op-amp that is used in the continuous
analog blocks. This op-amp then has various capacitors linked with switching signals
placed in feedback, input, and output positions so as to serve various functions such
as integrators, summers and filters. These capacitors are linked to timed switching
signals. Together, they have an ability to function the same as a resistor would in the
circuit. The value of the capacitance along with the speed of the switching allows the
user to vary the correlating resistance value. This is the heart of the switched capacitor
technology. Since switching is involved, the output signal that you would expect
isn’t continuously present and must be sampled at specific times in order to see the
correct signal. The construction of the PSoC switched capacitor blocks allows you
to process these signals easily in filters and put them out to the analog output buffers
or use the blocks as analog-to-digital converters without being a switched capacitor
expert. For those who are really adventurous, Cypress has created the generic
switched cap block. This block gives you a visual configuration of all the settings of a
switched capacitor block to allow you to create your own module easily.
There are two types of switched capacitor blocks on any particular PSoC part.
On the older parts 25xxx/26xxx, we noted that these blocks have an ‘A’ or a ‘B’
designation. On the newer parts such as the 27xxx, these blocks have a ‘C’ or ‘D’
designation. The new references are due to some improvements in the switched cap
blocks and are used to differentiate these blocks from the older technology.

Switched cap blocks can output their signal to the analog output buffers, which
allow you to output a filtered signal or use a switched cap block as a digital-to-analog
converter (DAC). You can also send your signal to other blocks for further processing.
Using this type of system, I can bring a analog signal into the PSoC, amplify
that signal, direct the amplified signal through a bandpass filter, run the output of the
filter through a analog-to-digital converter, read the value of the analog-to-digital
filter to perform some digital signal processing and then output the result of the
digital signal processing to a DAC signal to be output on an I/O pin to the system
external to the PSoC.

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