Bandgap Reference Voltage Calibration Circuit
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Solution Overview
Problem
Conventional reference voltage generating circuits in integrated circuits face significant variations due to non-zero offset voltages in operational amplifiers, leading to drift in bandgap voltage values from chip to chip, which existing techniques like trimming circuits and chopper stabilization fail to adequately address without increasing complexity or area consumption.
Innovation Solution
A calibration method and circuit that alternately operates the bandgap unit in two modes to generate and adjust control codes for calibration voltages, averaging these codes to eliminate offset voltage variations and stabilize the bandgap voltage, thereby reducing chip-to-chip variation without requiring a low pass filter or high frequency modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trimming circuit is used to reduce reference voltage variation, then chip-to-chip variation is reduced, but device complexity and manufacturing time increase
Solution Approach 1:
The patent extracts the offset voltage error from the reference voltage generation process by using a separate calibration phase. The operational amplifier's offset voltage is measured and compensated independently through switching configurations, removing the harmful effect without requiring complex trimming circuits or additional offset cancellation hardware in the main reference voltage path.
Solution Approach 2:
The patent performs preliminary calibration of the operational amplifier's offset voltage before the reference voltage is put into service. By pre-measuring and compensating for the offset voltage through switching the amplifier in different configurations and storing the calibration data, the system eliminates offset effects before they can cause chip-to-chip variation, avoiding the need for complex real-time correction circuits.
2Reliability
If chopper stabilization is used to reduce offset variation, then reference voltage stability is improved, but device complexity and area consumption increase
Solution Approach 1:
The patent employs periodic switching of the operational amplifier between different input configurations to measure and compensate for offset voltage. By alternately connecting the amplifier in unity-gain and inverting configurations, the system periodically samples the offset voltage and uses this information to correct the reference voltage, achieving stabilization without requiring continuous high-frequency modulation circuits.
Solution Approach 2:
The patent creates a copy of the operational amplifier's offset voltage error through switching configurations and uses this copied error signal to generate a compensating correction voltage. By measuring the offset in one configuration and applying the opposite correction in another configuration, the system cancels the offset effect without needing additional dedicated offset cancellation hardware.
3Measurement precision
If high gain operational amplifier is used to achieve equal base-emitter voltages, then bandgap voltage accuracy is improved, but sensitivity to offset voltage increases
Solution Approach 1:
The patent introduces feedback by measuring the operational amplifier's offset voltage through switching configurations and using this measurement to generate a correction voltage that is fed back to compensate for the offset. The high-gain amplifier continues to operate at full gain for accuracy, while the feedback loop separately measures and corrects the offset voltage, decoupling the amplifier's gain function from its offset sensitivity.
Solution Approach 2:
The patent changes the operational parameters of the operational amplifier by switching between different input configurations (unity-gain and inverting modes). By varying the configuration parameter, the system measures the offset voltage in one state and applies correction in another state, allowing the amplifier to maintain high gain while compensating for offset voltage variations that cause chip-to-chip inconsistency.
Data Source
AI summary
A reference voltage device and a reference voltage generating method thereof. The reference voltage device comprises a bandgap unit, a voltage generating unit, a comparator, and a calibration controller. The calibration controller controls the voltage generating unit to generate a final calibrating voltage to serve as an ideal target voltage. The bandgap unit generates a bandgap voltage with zero offset voltage according to the final calibrating voltage to serve as a reference voltage. The variation of the reference voltage output by the reference voltage device is thus reduced.