Auto-nulled Bandgap Reference Circuit for Offset and Noise Reduction
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Solution Overview
Problem
MOS devices in reduced feature set semiconductor processes exhibit larger and less predictable device mismatch levels, leading to increased noise and voltage shifts over temperature, which are undesirable in voltage references.
Innovation Solution
An auto-nulled bandgap reference system employing a substrate PTAT bandgap reference circuit with primary and auxiliary amplifiers and a switching circuit that nulls offset and noise errors, along with a strobed bandgap reference circuit that periodically powers up to refresh the voltage reference and conserve power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If MOS devices are used in reduced feature set processes, then manufacturing cost is reduced and device integration is improved, but device mismatch increases and noise levels increase
Solution Approach 1:
The patent extracts the problematic MOS amplifier from the reference circuit path by using it only for nulling offset and noise, while the main reference signal is taken from a substrate bipolar bandgap core that does not require MOS amplifiers for signal generation
Solution Approach 2:
The patent introduces an auxiliary substrate bipolar bandgap core as an intermediary to provide a clean reference signal that is free from MOS amplifier noise, while the MOS amplifier serves only to null offset errors in the main signal path
2Ease of manufacture
If MOS devices are used in reduced feature set processes, then manufacturing cost is reduced, but noise levels increase
Solution Approach 1:
The patent extracts the noise-generating MOS amplifier from the main reference signal path and uses it only for offset nulling, while the main reference signal comes from a substrate bipolar bandgap core that generates minimal noise
Solution Approach 2:
The patent employs periodic strobing to refresh the reference voltage at controlled intervals, allowing the MOS amplifier to be activated only when needed for nulling, thereby reducing its noise contribution to the overall system
3Measurement precision
If amplifier offset and noise are reduced through auto-nulling, then temperature coefficient precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the bandgap reference system into two independent cores: a main substrate bipolar bandgap core for generating the reference voltage and an auxiliary substrate bipolar bandgap core for providing a clean signal and offset nulling, allowing each segment to be optimized independently
Solution Approach 2:
The patent introduces an auxiliary substrate bipolar bandgap core as an intermediary that provides a clean reference signal free from MOS amplifier noise and offset, which then serves as the input to the MOS amplifier for nulling operations
4Measurement precision
If continuous operation is maintained for accurate reference voltage, then precision is maintained, but power consumption increases
Solution Approach 1:
The patent employs periodic strobing to refresh the reference voltage at controlled intervals rather than maintaining continuous operation, allowing the circuit to enter low-power states between refresh cycles while maintaining precision through periodic updates
Solution Approach 2:
The patent uses output storage capacitors to hold the reference voltage between refresh cycles, discarding the continuous power consumption and recovering the voltage state through periodic refresh operations that restore the capacitors
Data Source
AI summary
An auto-nulled bandgap reference system employing a substrate bandgap reference circuit with primary and auxiliary amplifiers and a switching circuit which in a first mode develops a voltage to null the offset and noise errors of the auxiliary amplifier and then in the second mode uses the nulled auxiliary amplifier to develop a voltage to null the offset and noise errors of the primary amplifier; and a strobe circuit including an output storage device and a strobe control circuit for periodically powering up a bandgap reference circuit to charge the output storage device and powering down the bandgap reference circuit to conserve power.