Ths paper analyses the tonal behaviour of the quantization noise in 2nd-order bandpass SD modulators. The analysis previously performed for lowpass modulators is extended to the bandpass case. As a result, closed-form expressions for the frequency of the idle tones are derived for different locations of the signal center frequency. The analytical results are validated through measurements from a silicon prototype realized using fully differential switched-current circuits in a standard 0.8μm CMOS technology.This work has been supported by the Spanish CICYT Project TIC 97-0580.Peer reviewed