A millimeter and sub-millimeter wavelength receiver imaging apparatus and method which directly generates a time encoded digital signal for an imaging pixel in response to interoperation of a digital quench circuit, an envelope detector, and a regenerative oscillator coupled to an antenna. The device utilizes the fact that oscillator startup time in a regenerative oscillator is inversely proportional to injected pixel image power. A digital quench circuit, such as a latch, is coupled for activating and deactivating the regenerative oscillator in response to receiving an output from an envelope threshold circuit, and for generating a time encoded digital signal in response to pixel amplitude during millimeter and sub-millimeter wavelength imaging. Receiver embodiments are described for both fundamental frequency operation (DRR) and for multi-frequency imaging (IRR).