Abstract: Apparatus and methods for transceivers are provided herein. In a first aspect, an observation receiver is implemented to detect common-mode local oscillator (LO) leakage while the observation receiver performs other functions. In a second aspect, a transceiver is implemented with an LO leakage compensation circuit that compensates a transmitter for LO leakage using a digital filter, such as a Kalman filter, that combines differential LO leakage observations with common-mode LO leakage observations. In a third aspect, a transmitter includes multiple local loopback paths including a first loopback path after a variable gain amplifier (VGA) and a second loopback path before the VGA.