Improved linearity programmable voltage reference

The design of a programmable voltage reference for a digital control dc-dc power converter is presented. Propagation time errors on the analog pulse density modulated output signal lead to integral non linearity (INL) errors on the transfer characteristic of the programmable reference. Multi-bit sigma-delta (ΣΔ) modulation is proposed to remove this source of INL error. The programmable reference based on multi-bit ΣΔ modulation must include a dynamic element matching scheme and a low offset amplifier to remove sources of error introduced by this approach. INL performance of the single bit and multi-bit schemes is verified by transistor level simulation.