Bandgap Reference Circuit Start-Up Logic for Stable Operating Point

The patent applies preliminary action by using a start-up circuit that proactively forces the bandgap circuit into the desired operating state before normal operation begins. The start-up transistor is turned on initially to establish proper current flow through the diodes and resistors, ensuring the circuit settles at the correct operating point. After stabilization, the start-up transistor is turned off, leaving the circuit in the desired state without risk of settling at the zero-current stable point.

The patent applies the extraction principle by completely isolating the start-up circuit from the main feedback loop after it has performed its stabilization function. A isolation transistor is used to disconnect the start-up circuit's current path from the feedback network. This ensures that once the bandgap circuit reaches its operating state, the start-up circuit cannot influence it and cause the system to settle at unwanted stable states including the zero-current state.

The patent introduces an intermediary start-up transistor that mediates between the reset control signal and the bandgap circuit's operating state. This transistor acts as a controlled switch that manages current flow during the critical transition period. When activated by the reset signal, it ensures proper biasing conditions are established before disconnecting, thereby preventing the circuit from settling at the zero-current stable state while maintaining relatively simple overall circuit structure.