ACMP - Analog Comparator

Description

Analog comparator (ACMP) Peripheral API.

The Analog Comparator is used to compare voltage of two analog inputs with a digital output indicating which input voltage is higher. Inputs can either be one of the selectable internal references or from external pins. Response time and current consumption can be configured by altering the current supply to the comparator.

ACMP is available down to EM3 and is able to wake up the system when input signals pass a certain threshold. Use ACMP_IntEnable() to enable an edge interrupt to use this functionality.

This example shows how to use the em_acmp.h API for comparing an input pin to an internal 2.5 V reference voltage.

/* The ACMP is a high-frequency peripheral so we need to enable
* both the HFPER clock and the ACMP0 clock. */
CMU_ClockEnable ( cmuClock_HFPER , true );
CMU_ClockEnable ( cmuClock_ACMP0 , true );
/* Initialize with default settings. */
ACMP_Init_TypeDef init = ACMP_INIT_DEFAULT ;
init. enable = false ;
ACMP_Init (ACMP0, &init);
/* In this example we want to compare an analog input to the 2.5 V
* internal reference. To achieve this we first have to configure the
* VB source which is used for internal reference voltages. */
ACMP_VBConfig_TypeDef vbconfig = ACMP_VBCONFIG_DEFAULT ;
vbconfig. input = acmpVBInput2V5 ;
ACMP_VBSetup (ACMP0, &vbconfig);
/* Now we select the two inputs to compare. Here we compare the APORT0XCH0
* input to the internal 2.5V reference that we previously configured. When
* APORT0XCH0 is lower than 2.5 V then the ACMP output is 0 and when
* APORT0XCH0 is is higher than 2.5 V then the ACMP output is 1. */
ACMP_ChannelSet (ACMP0, acmpInputVBDIV , acmpInputAPORT0XCH0 );
/* To be able to probe the output we can send the ACMP output to a pin.
* The second argument to this function is the pin location which is
* device dependent. */
ACMP_GPIOSetup (ACMP0, 0, true , false );
/* Finally we enable the ACMP. */
ACMP_Enable (ACMP0);
Note
ACMP can also be used to compare two separate input pins.

ACMP also contains specialized hardware for capacitive sensing. This module contains the ACMP_CapsenseInit() function to initialize ACMP for capacitive sensing and the ACMP_CapsenseChannelSet() function to select the current capsense channel.

For applications that require capacitive sensing it is recommended to use a library, such as cslib, which is provided by Silicon Labs.