Chopper Amplifier Gain Control for Stable Bandwidth
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Solution Overview
Problem
Existing chopper amplifiers face instability in effective gain due to variations in bandwidth and settling time, leading to gain reduction and potential errors, especially when adjusting closed-loop gain settings.
Innovation Solution
The amplifier incorporates a first and second chopper circuit with operational amplifiers and variable resistors and capacitors, allowing for adjustable resistance and capacitance values based on control signals, stabilizing the gain bandwidth product and ensuring consistent performance across different gain settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the current value IDD of the drive current is increased to increase the gain bandwidth product GBW, then the bandwidth BW is improved, but power consumption increases
Solution Approach 1:
The patent applies dynamics by making the drive current IDD variable rather than fixed. The current value changing unit dynamically adjusts the drive current based on the closed-loop gain setting, allowing the operational amplifier to operate at optimal current levels for different gain configurations. This resolves the contradiction by enabling high bandwidth when needed (high current) while reducing power consumption during low-bandwidth operations (lower current).
Solution Approach 2:
The patent changes the parameter of drive current from a static value to a dynamically adjustable parameter. By controlling the drive current to vary with the closed-loop gain setting, the system can optimize the gain bandwidth product GBW for each operating condition without continuously consuming maximum power, thus resolving the trade-off between bandwidth and power consumption.
2Speed
If the capacitance value Cc of phase compensation capacitance is decreased to increase the gain bandwidth product GBW, then the bandwidth BW is improved, but phase margin becomes insufficient causing ringing
Solution Approach 1:
The patent changes the parameter of phase compensation capacitance from a fixed value to a variable parameter that adapts to different operating conditions. The capacitance value changing unit adjusts the capacitance value based on the closed-loop gain setting, ensuring sufficient phase margin is maintained across all gain configurations. This resolves the contradiction by allowing the system to achieve high bandwidth when appropriate while preventing ringing and instability when phase margin is critical.
3Measurement precision
If the closed-loop gain is adjusted to match sensor dynamic range, then measurement precision is improved, but effective chopper amplifier gain becomes unstable due to bandwidth variations
Solution Approach 1:
The patent implements feedback by having the current value changing unit and capacitance value changing unit respond to the closed-loop gain setting. This creates a closed-loop control system where the drive current and phase compensation capacitance are automatically adjusted based on the selected gain configuration. This feedback mechanism ensures that the gain bandwidth product remains constant across different gain settings, resolving the stability issue while allowing precise measurement optimization.
Solution Approach 2:
The patent dynamically adjusts multiple parameters (drive current, phase compensation capacitance) in response to closed-loop gain changes. This coordinated parameter adjustment ensures that the gain bandwidth product GBW remains constant regardless of the closed-loop gain setting, thereby maintaining stable effective chopper amplifier gain while enabling precise sensor signal measurement across different dynamic ranges.
4Speed
If a high clock frequency is set to achieve high-speed response for wide bandwidth input signal, then speed is improved, but the time constant t becomes insufficient leading to settling error and gain reduction
Solution Approach 1:
The patent applies dynamics by making the drive current variable based on the clock frequency and gain setting. When high clock frequency is used for fast response, the system increases the drive current to ensure the time constant is sufficiently short to complete settling within the available time. This dynamic current adjustment resolves the contradiction by providing both high-speed response capability and sufficient settling accuracy when needed.
Data Source
AI summary
An amplifier includes: input terminals; chopper circuits capable of switching between a direct connection state and a cross connection state; resistors; a variable resistor; an operational amplifier, including an input port connected to an output port, a control port receiving a control signal, and an input port connected to one end of the resistor and one end of the variable resistor; an operational amplifier, including an input port connected to an output port, a control port receiving a control signal, and an input port connected to one end of the resistor and the other end of the variable resistor; and output terminals. The operational amplifiers are configured to switch their gain bandwidth product based on the control signal.