Comprehensive study of Howland circuit with non-ideal components to design high performance current pumps

• Equations are derived for designing high performance Howland current pumps.
• Three main design parameters are introduced to adjust the characteristics of the pump.
• Simulations and experimental measurements validated the derived equations.
• Different configurations of Howland circuit are compared for their performance.
• Equations are used to design a high performance pump for an impedance cardiograph.

Howland circuit is a popular high performance, voltage-controlled current pump, which can both sink and source precise amounts of current and provide high output impedance as well as high frequency bandwidth. In this article, analytical expressions are derived for performance characteristics of non-ideal Howland Current Pump, and it is shown that the main characteristics can be adjusted using three independent parameters: resistors’ scale, feedback ratio, and current sensing resistor’s value. The derived expressions are evaluated by computer simulations, and then are used to design a current pump for an impedance cardiography system, as an example. Performance of the circuit is evaluated based on simulations and experimental tests, and then is compared with several previous designs in the literature. The relationships provide a unified framework for the analysis of different configurations of Howland current pump and can facilitate its design process for different applications with specific performance requirements.