The manufacturer’s circuit for a precision, current-mode, full-wave rectifier (Fig 1a) converts a voltage signal to a current, eliminating errors arising from voltage drops across the rectifying diodes. However, just like op-amp-based rectifiers, the circuit in Fig 1a requires closely matched resistors.
The circuit in Fig 1b obviates the precision resistors by simply returning the diodes to the input. For a positive signal current, D1 is on, and the current flows into the load resistor to develop an output voltage.
When the input signal current is negative, D2 is on, passing current to the low-impedance input X of current-conveyor PA630, IC1 (Photonics, Manotic, ON, Canada, (613) 652-2247). IC1 conveys this current via its high-impedance output Z to the load. This current flows in the same direction as current that D1 passes because IC1 inverts current flows. The circuit provides glitch-free performance up to 1 MHz. (DI #1426)