32-bit Configurable bias current generator with sub-off-current capability

Abstract

A fully configurable bias current reference is described. The output of the current reference is a gate voltage which produces a desired current. For each daisy-chained bias, 32 bits of configuration are divided into 22 bits of bias current, 6 bits of active-mirror buffer current, and 4 bits of other configuration. Configuration of each bias allows specifying the type of transistor (nfet or pfet), whether the bias is enabled or weakly pulled to the rail, whether the bias is for a cascode, and whether the bias transistor uses a shifted source (SS) voltage for sub-off-current biasing. In addition, the current reference integrates a pair of voltage regulators that generate stable voltage sources near the rails, suitable for the SS current references. Measurements from fabricated current references built in 180 nm CMOS show that the reference achieves at least 110 dB (22-bit) dynamic range and reaches 160dB when power-rail gate biasing is included. Generated bias currents reach at least 30x smaller current than the transistor off-current. Each current reference occupies an area of 620 × 50 um2. The design kit schematics and layout are open-sourced.