The circuit of Figure 1 comprises a loop-powered 4-20 mA precision transmitter (MAX4236, BSP149, and MAX6138A) with large-compliance output stage, and a precision pulse width modulated (PWM) signal ...

Several decades ago, as signal-conditioning circuits and their A/D and D/A converters greatly reduced their power needs, it became practical to operate that circuitry from the few mA of available ...