A hands-on approach to differential circuit measurements

Abstract

Electronic engineering is showing a definite trend towards differential circuits. However, most measurement instruments are single-ended. Consequently, engineering graduates often lack the skills to perform correct differential measurements. This paper describes the theoretical background, development and limitations of three experiments that help students to gain insight into differential measurements and the origin and consequences of a low common-mode rejection ratio. The experiments require only common equipment and suit both electrical and non-electrical engineering students.

Common mode electronic noise in differential circuits

“…That subtraction results in negative correlation between the output voltages of the two signal paths of the differential circuit and if these two paths were matched, then input common-mode noise would be totally rejected upon subtracting their outputs. Mismatches between the two signal paths, however, limit noise reduction according to factor k NR defined in (15), which should ideally be 1. High CMRR values for the entire signal bandwidth yield k NR % 1 and they can be obtained by high CMRR(0) and similar gain-bandwidth product for the two signal paths (GBW 1 % GBW 2 ), the first condition being more important.…”

“…For a differential circuit like that in Fig. 1, where the two signal paths in the first stage are independent from each other, according to [14,15] we have,…”

Unconventional Double-Current Circuit for Deflection and Temperature Simultaneous Measurement

“…Most of those systems are based on measuring one quantity [3], [4]. However, a group of measurement methods which are used to measure several quantities at the same time is also worth noticing [5]- [8].…”

Self-testing of fully differential multistage circuits using common-mode excitation

“…Differential signal processing provides many advantages, the main include: the 6 dB improvement in dynamic range when compared to the singleended circuits, the ability to easily process alternating signals in systems operating from single power supplies, increased immunity to outside electromagnetic interference, very high power-supplyrejection-ratio, cancellation of even-order harmonics. The number of components in a fully differential circuit is approximately double that of a single-ended circuit but FD circuits are increasingly common in both analog and digital electronics [3].…”