Band-gap Reference Voltage Source Circuit Start-up Mechanism
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Solution Overview
Problem
Band-gap reference voltage source circuits face a zero-current state during power-on events due to low input voltages, preventing initial operation and requiring a mechanism to force current flow during transient periods.
Innovation Solution
Incorporating a detector block that monitors the rising power-supply voltage and uses resistive voltage dividers to invert signals, ensuring current flow to the diode-pair circuit, and employing a bias generator to stabilize the reference voltage output by using a second differential amplifier as a voltage-follower circuit to maintain a stable start-up condition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power-supply voltage is low during power-on events, then the circuit cannot start operation due to zero current state, but increasing the power-supply voltage directly does not ensure reliable start-up
Solution Approach 1:
The detector block monitors the power-supply voltage in advance and activates the pull-up transistor MP15 before the main operation begins. When the voltage reaches a predetermined level, the detector triggers the pull-up action to force current flow through the diode-pair circuit, ensuring the circuit is ready for operation before full power is applied.
Solution Approach 2:
The detector block acts as an intermediary between the power-supply voltage and the main circuit operation. It detects the voltage level and controls the pull-up transistor MP15 to force current flow when needed, mediating the transition from low-voltage standby to full operation without requiring direct manual intervention or complex control logic.
2Reliability
If a detector block with pull-up transistor is added to force current flow during transient periods, then start-up reliability improves, but device complexity increases
Solution Approach 1:
The detector block and pull-up transistor MP15 are configured to activate automatically when the power-supply voltage reaches a predetermined level, forcing current flow through the diode-pair circuit before main operation begins. This preliminary action ensures reliable start-up without requiring complex external control mechanisms.
Solution Approach 2:
The detector block automatically monitors the power-supply voltage and controls the pull-up transistor MP15 based on detected voltage levels. The circuit serves itself by detecting its own operating conditions and activating the necessary components without external intervention, reducing the need for additional control circuitry.
3Use of energy by moving object
If the differential amplifier operates with low input voltages, then power consumption is reduced, but the circuit enters a zero-current state and cannot operate
Solution Approach 1:
The pull-up transistor MP15 is activated in advance when the power-supply voltage reaches a predetermined level, forcing current flow through the diode-pair circuit before the differential amplifier needs to operate. This ensures the circuit is in a valid operating state with sufficient current flow before low-power operation begins.
Solution Approach 2:
The circuit dynamically transitions between different operating states: during power-on, the pull-up transistor MP15 forces current flow to establish operation; once operational, the circuit maintains appropriate current levels through the differential amplifier's feedback mechanism, adapting to power-supply voltage variations while ensuring minimum operating current is maintained.
Data Source
AI summary
A band-gap reference voltage source circuit is constituted of a diode-pair circuit connected to a reference voltage output terminal, a first differential amplifier including a first transistor and a first operational amplifier, and a second differential amplifier including a second transistor and a second operational amplifier. The second differential amplifier operates based on a bias voltage, which is lower than a predetermined voltage, so as to forcedly pull up the level of the reference voltage output terminal via the second transistor before the first differential amplifier starts to pull up the level of the reference voltage output terminal up to the predetermined voltage via the first transistor.