Switched-Capacitor Feedback Resistor for Stable Amplifier Corner Frequency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing amplifiers face challenges in maintaining a low high-pass corner frequency across temperature variations while requiring high input impedance, especially in low-power applications, which is exacerbated by small feedback capacitors and high resistance needs.
Innovation Solution
The implementation of a sample and average common mode feedback resistor, comprising a low pass filter in series with a switched capacitor resistor, coupled with a control circuit to supply drive signals, allowing for programmable corner frequency and reduced temperature sensitivity, achieving a resistance of 100 TΩ in a 180 nm CMOS implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traditional feedback resistor is used to establish input common-mode voltage, then input offset cancellation is achieved, but the high-pass corner frequency becomes too high due to the need for tens of teraohms of feedback resistance
Solution Approach 1:
The patent changes the resistance value parameter dynamically using a switched capacitor resistor that can be programmed to different resistance values (e.g., 100 TΩ, 1 TΩ, 100 GΩ) through control signals. This allows the high-pass corner frequency to be adjusted while maintaining input offset cancellation functionality.
Solution Approach 2:
The feedback resistor is made dynamic through the switched capacitor implementation, allowing the resistance to change over time based on control signals. This enables the system to adapt the high-pass corner frequency to different operating conditions while maintaining low-power operation.
2Use of energy by moving object
If a small feedback capacitor is used to achieve high input impedance in low-power applications, then power consumption is reduced, but the high-pass corner frequency increases further
Solution Approach 1:
The patent compensates for the high-pass corner frequency increase caused by small feedback capacitors by dynamically adjusting the feedback resistor value through the switched capacitor network. The control circuit programs the resistor to achieve the desired corner frequency while maintaining the low power consumption benefit of the small capacitor.
3Device complexity
If a fixed feedback resistor is used, then the circuit is simple, but the corner frequency cannot be programmed and temperature sensitivity is high
Solution Approach 1:
The patent implements a dynamic switched capacitor resistor controlled by control signals that can program different resistance values. This adds programmability for corner frequency adjustment while maintaining reasonable circuit complexity through the use of standard CMOS switches and capacitors.
Solution Approach 2:
The switched capacitor resistor serves multiple functions: it provides programmable resistance values for corner frequency control, maintains low power consumption, and reduces temperature sensitivity. This multi-functional element replaces what would otherwise require separate components for each function.
4Reliability
If traditional pseudo-resistor implementations are used, then the feedback resistance is achieved, but temperature stability is poor and power consumption is higher
Solution Approach 1:
The patent replaces traditional pseudo-resistor implementations with a switched capacitor network that uses electronic switching instead of resistive elements. This substitution achieves the same feedback resistance function with better temperature stability and lower power consumption by using capacitors and switches rather than resistors.
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
This solution effectively controls the high-pass corner frequency across temperature, reduces power consumption, and maintains reliable performance across a wide range of temperatures and process variations, with improved stability and programmability compared to traditional pseudo-resistor implementations.
Implementation Method 1
the feedback resistor is comprised of a low pass filter in series with a switched capacitor resistor
Implementation Method 2
the feedback resistor is comprised of a low pass filter in series with a switched capacitor resistor
Data Source
AI summary
An amplifier is presented with a sample and average common mode feedback resistor. The amplifier circuit includes a feedback capacitor and a feedback resistor in parallel with the feedback capacitor, where the feedback capacitor and the feedback resistor form part of the negative feedback path for the amplifier. Of note, the feedback resistor is comprised of a low pass filter in series with a switched capacitor resistor, such that the low pass filter is electrically coupled to the output of the amplifier circuit and the switched capacitor resistor is electrically coupled to the inverting input of the amplifier circuit. The amplifier circuit further includes a control circuit interfaced with switches of the switched capacitor resistor. The high pass corner of the switched capacitor resistor is preferably lower than corner of the low pass filter.