Chopper-Stabilized Bandgap Reference Voltage Circuit with Switched-Capacitor Filter
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Solution Overview
Problem
Conventional bandgap reference (BGR) circuits used in semiconductor devices face accuracy issues due to offset voltages caused by element variations, which are not effectively addressed by existing chopper stabilized BGR circuits that require larger circuit scales to achieve low current consumption and small occupied area.
Innovation Solution
A reference voltage generating circuit incorporating a chopper stabilized BGR circuit with a moving average filter LPF circuit, where the LPF circuit's properties are not dependent on passive element values, allowing for efficient removal of offset voltage components while maintaining a small circuit scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an RC filter is used as the LPF circuit to remove offset voltage components, then the offset voltage can be effectively removed, but the area occupied by the LPF circuit becomes larger and the circuit scale increases
Solution Approach 1:
The patent changes the fundamental parameter of the filter circuit from passive RC components to active switched-capacitor components. By using capacitive elements with switch circuits controlled by clock signals, the filter characteristics are determined by capacitance ratios and switching frequencies rather than resistance and capacitance absolute values. This allows achieving the same filtering effect with much smaller component values, reducing the overall circuit area while maintaining reference voltage accuracy.
2Measurement precision
If the chopper frequency is set high to improve offset voltage removal, then the offset voltage component can be more effectively converted to AC, but the settling time requirement cannot be met and current consumption increases
Solution Approach 1:
The patent employs periodic switching action through clock signals to alternately connect and disconnect the capacitive elements. This periodic action converts the DC offset voltage into an AC signal at the clock frequency, which can then be filtered out. By using periodic switching rather than continuous high-frequency operation, the circuit achieves effective offset removal while allowing the operational amplifier to settle during non-switching periods, thus maintaining lower current consumption.
3Measurement precision
If the cutoff frequency of the LPF circuit is set lower than the chopper frequency to remove offset voltage, then the offset voltage component can be removed, but the resistance and capacitance values must be larger increasing the circuit area
Solution Approach 1:
The patent substitutes the traditional passive RC filtering mechanism with an active switched-capacitor filtering mechanism. Instead of relying on resistive and capacitive time constants, the new system uses capacitive charging and discharging through switches controlled by clock signals. This substitution enables the filter cutoff frequency to be determined by the switching frequency and capacitance ratios rather than by large passive component values, thereby reducing circuit complexity and scale while achieving the required offset voltage removal.
Data Source
AI summary
A reference voltage generating circuit including a bandgap reference circuit generating a bandgap reference voltage, and a filter circuit smoothing the bandgap reference voltage. The bandgap reference circuit is configured to generate the bandgap reference voltage having a first voltage value when a clock signal is in a first logic level, and to generate the bandgap reference voltage having a second voltage value when the clock signal is in a second logic level. The filter circuit includes a first capacitive element charged with the bandgap reference voltage having the first voltage value in the first clock cycle, a second capacitive element charged with the bandgap reference voltage having the second voltage value in the first clock cycle, a third capacitive element charged with the bandgap reference voltage, and a fourth capacitive element.