Traditionally, ultrasonic ranging sensors emit pulse trains. The distance traveled by the received signal is calculated from its delay with respect to the emitted signal. There are different strategies to encode the signal in order to determine the delay. In this paper we present a method for encoding amplitude that encodes the amplitude of a signal formed by rectangular pulse trains whose frequency is 40 kHz. The pulse amplitude is encoded in a binary manner according to a pseudorandom sequence. Owing to that the emitted signal is formed by pulse trains whose amplitude is modulated, the impulse response of the designed system generates sinusoidal pulse trains whose amplitude is variable. The proposed strategy uses the phase of signal to position temporally each pulse trains. This positioning has higher precision than the sampling time of the signal.