The Improved Howland current pump is a circuit that uses a difference amplifier to impose a voltage across a shunt resistor, creating a voltage-controlled current source capable of driving a wide range of load resistances. This versatility of this design can be useful in many applications that require a current source capable of bipolar (source or sink) operation. Part of the versatility is the ability to make small alterations to the design that improves the overall performance of the circuit. This article analyzes a few Improved Howland current pump configurations and provides recommendations on how to enhance performance.
A common goal of these designs is to create a high-output impedance current source that can source or sink approximately 25 mA of current while employing the Improved Howland current pump topology. Analysis is done on four different configurations and some benefits and disadvantages of each configuration is discussed. Depending on design requirements, one configuration can be more appropriate than another for a specific application. Take precautions when driving reactive loads in an Improved Howland current pump circuit. Additionally, some loads can cause the circuit to become unstable due to insufficient phase margin. Only resistive loads are discussed in this article.