The disclosed invention provides apparatus and methods that can convert frequencies of time-encoded signals. In one aspect, a down-converter circuit includes low-pass filters, a switch, a time encoder, and an output low-pass filter. In another aspect, an up-converter circuit includes an analog or digital input time encoder, low-pass filters, a switch, an output time encoder, and a time-encoded band-pass filter. In yet another aspect, a complete receiver system is provided. The receiver system can operate effectively with signals in the radio frequency range.