On the bandwidth of carrier-type dc amplifiers

For a carrier-type amplifier (e.g., a chopper amplifier), it is well known that the low-frequency response may extend to dc. The position regarding the high-frequency response is not as clear, and statements in the literature give various fractions of the fundamental carrier frequency as an upper limit to the input-signal bandwidth that can be recovered from the modulated carrier. It is argued here that there is no simple well-defined theoretical upper limit, and that in practical circuits the fundamental carrier frequency may or may not be one of several factors determining the useful bandwidth. The circuit of a novel wide-band dc amplifier, consisting of two synchronized chopper amplifiers operating in parallel, is described. The frequency response of this amplifier is independent of the chopping rate, and its method of operation may help clarify bandwidth limitations.