Measuring Amplifier Based on Hamon Resistors and Dynamic Element Matching Technology

Abstract

In this paper a principle of combination of the Hamon resistors (HR) and dynamic element matching (DEM) technology used in resistance feedback network of measuring amplifier (H - DEM amplifier) is presented. The nominal gain factor of this amplifier does not depend on the values of its feedback resistors but depends exclusively on the internal resistor's number. The mean value of the gain is obtained by cyclically shifting of the four Hamon resistors along all four positions in the feedback network. In this shifting, the Hamon internal resistors, which are located between the inputs of the two operational amplifiers, are connected in parallel, while the rest are connected in series. Precision of amplifier can be realized with easily available resistors with even a few tenths of a percent tolerance, because it inaccuracy is proportional to the square of resistor tolerance. In comparison with usual amplifiers based on DEM technology, in which the number of cylices of the feedback resistors shifting is equal to the number of feedback resistors, i.e. depend on gain value, in H-DEM amplifier the number of shifting is always equal to four independently on the gain value. Due to this the bandwidth of the amplified signal is much wider compared to the bandwidth of the amplifier based on DEM technology. Besides it, when the gain must be more than of few tens or more, the H-DEM amplifier needs a few times less resistors and switches in comparison with DEM amplifier.