Texas Instruments MSP430x1xx manual Output Filter, Voltage Reference Generator

Comparator_A Operation

16.2.3 Output Filter

The output of the comparator can be used with or without internal filtering. When control bit CAF is set, the output is filtered with an on-chip RC-filter.

Any comparator output oscillates if the voltage difference across the input terminals is small. Internal and external parasitic effects and cross coupling on and between signal lines, power supply lines, and other parts of the system are responsible for this behavior as shown in Figure 16−2. The comparator output oscillation reduces accuracy and resolution of the comparison result. Selecting the output filter can reduce errors associated with comparator oscillation.

Figure 16−2. RC-Filter Response at the Output of the Comparator

+ Terminal

− Terminal Comparator Inputs

Comparator Output

Unfiltered at CAOUT

Comparator Output

Filtered at CAOUT

16.2.4 Voltage Reference Generator

The voltage reference generator is used to generate VCAREF, which can be applied to either comparator input terminal. The CAREFx bits control the

output of the voltage generator. The CARSEL bit selects the comparator

terminal to which VCAREF is applied. If external signals are applied to both comparator input terminals, the internal reference generator should be turned

off to reduce current consumption. The voltage reference generator can generate a fraction of the device’s VCC or a fixed transistor threshold voltage of ~ 0.55 V.

Comparator_A 16-5