currentmode

Current mode is a class of electronic circuit techniques in which signal information is carried primarily by currents rather than voltages. In current-mode circuits, most nodes are driven by current sources or sinks, often using current mirrors, current conveyors, and current-steering transistors. This approach contrasts with voltage-mode circuits, where information is encoded in voltage levels and currents adapt to the load.

Common implementations include current-mode logic (CML), transconductance amplifiers, current conveyors, and current-mode filters. CML uses differential pairs and current steering to represent logic with a near-constant current and a small voltage swing, enabling high-speed operation and good noise immunity for certain layouts. Transconductance-based paths convert voltages into currents, allowing current-mode processing of signals.

Advantages of current-mode designs include high bandwidth due to reduced node capacitance and the ability to process signals with little voltage swing, which can improve isolation from supply noise. They are well suited for high-speed data paths, wideband signal processing, and certain analog front-ends. Disadvantages include the need for precise current sources and mirrors, sensitivity to matching and temperature variations, and often higher static power consumption compared with some voltage-mode implementations.

Applications span high-speed digital circuits, phase detectors, DAC and ADC front-ends, and analog signal-processing blocks that benefit from current steering or current summation. The approach has historical roots in current-steering logic and ECL-style circuits and remains relevant in modern CMOS and bipolar technologies where fast, low-swing signaling is advantageous.