Capacitive Start-Up Circuit for Bandgap Reference Initialization
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Solution Overview
Problem
Conventional start-up circuits for bandgap voltage reference circuits often cause excessive current flow, potentially damaging external circuits and introducing errors in output voltage, especially in smaller device fabrication sizes like 16 nm and 28 nm, due to their inability to efficiently initialize the circuit to the non-zero stable point without large currents.
Innovation Solution
A start-up circuit utilizing a capacitive voltage divider and differential amplifier configuration, including driver transistors and current mirrors, to control the initialization of the bandgap reference circuit, minimizing current flow and ensuring the circuit stabilizes at the non-zero operating point, thereby reducing the risk of damage to external circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional start-up circuit injects current into a transistor to force the bandgap reference circuit to a desired operating point, then the circuit can be initialised to the non-zero stable point, but large currents flow on the output which may damage external circuits
Solution Approach 1:
The patent introduces an intermediary start-up circuit comprising a capacitive voltage divider and differential amplifier that mediates between the power supply and the bandgap reference circuit. This intermediary mechanism generates a controlled kick signal to initialise the circuit without allowing large currents to reach external circuits connected to the bandgap output.
Solution Approach 2:
The start-up circuit performs preliminary action by initialising the bandgap reference circuit to its non-zero stable point before normal operation begins. The capacitive voltage divider generates an initial kick signal that forces the circuit away from the zero stable point, ensuring proper operation before the start-up circuit is disabled.
2Reliability
If a conventional start-up circuit injects current to initialise the bandgap reference circuit, then the circuit stabilises at the non-zero operating point, but small amounts of current are drawn causing error in the output voltage
Solution Approach 1:
The start-up circuit employs dynamic operation where the capacitive voltage divider and differential amplifier are active only during initialisation. Once the bandgap reference circuit stabilises at its non-zero operating point, the start-up circuit automatically disables itself, ensuring no continuous current draw that would cause output voltage errors.
Solution Approach 2:
The start-up circuit operates periodically rather than continuously - it activates to provide an initial kick signal, then disables itself after initialisation is complete. This periodic operation eliminates continuous current draw that would otherwise cause measurement errors in the output voltage.
3Reliability
If the bandgap reference circuit is powered on with no external voltages applied, then it may stabilise at the zero operating point, but this produces no useful reference voltage
Solution Approach 1:
The start-up circuit applies preliminary anti-action by generating a kick signal that actively prevents the bandgap reference circuit from converging to the zero operating point. The capacitive voltage divider creates an initial voltage differential that forces the circuit toward the non-zero stable point, ensuring useful reference voltage generation from the outset.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed start-up circuit effectively initializes the bandgap reference circuit to the non-zero stable point with minimal current flow, reducing the risk of damage to external circuits and maintaining reasonable output currents, even in smaller device fabrication sizes.
Implementation Method 1
a capacitive voltage divider including a first capacitor in series with a second capacitor that generates a divider bias voltage between said first and second capacitors at a divider node
Implementation Method 2
a differential amplifier including a first amplifier input, a second amplifier input, and an amplifier output connected to the divider node
Implementation Method 3
a first driver transistor arranged such that a gate terminal of the first driver transistor is connected to the divider node, and a drain terminal of the first driver transistor is connected to both a first start-up output and the first amplifier input
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A start-up circuit (2) arranged to initialise a circuit portion (4) with a zero stable point (200) and a non-zero stable point (202). The start-up circuit comprises: a capacitive voltage divider including a first capacitor (16) and a second capacitor (18) that generate a divider bias voltage at a divider node (48); a differential amplifier including first and second amplifier inputs (20, 22) and an amplifier output connected to the divider node; a first driver transistor (12) with its gate terminal connected to the divider node, and its drain terminal connected to a first start-up output and the first amplifier input; and a second driver transistor (14) with its gate terminal connected to the divider node, and its drain terminal connected to a second start-up output and the second amplifier input. The differential amplifier controls the divider bias voltage and drives the circuit portion to the non-zero stable point.