1. A method comprising: generating a pulse signal based on a pseudorandom signal; responsive to a first level of the pulse signal, charging a sensing capacitor and a modulation capacitor; responsive to a second level of the pulse signal, discharging the sensing capacitor; generating a modulating signal based on an amount of charge stored on the modulation capacitor; and determining, based on a duty cycle of the modulating signal, whether an object is proximate to the sensing capacitor.