Chopper Amplifier Offset Tracking for Multi-Transistor Pair Switching
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Solution Overview
Problem
Chopper amplifiers experience input offset voltage and low frequency noise, such as flicker noise, which are not effectively compensated, leading to output signal corruption and the need for additional filtering, and transitioning between input transistor pairs results in delayed offset compensation.
Innovation Solution
A chopper amplifier with circuitry that includes multiple pairs of input transistors, an offset correction circuit that tracks and quickly updates input offset compensation signals, and digital circuitry for seamless switching, reducing input offset and low frequency noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a chopper amplifier uses a single pair of input transistors with conventional offset correction, then the circuit structure is simple, but the input offset voltage and low frequency noise are not effectively compensated
Solution Approach 1:
The offset correction circuit is segmented into multiple independent tracking circuits, each dedicated to tracking the offset of a specific input transistor pair. This segmentation allows each tracking circuit to independently and quickly respond to offset changes in its associated transistor pair, achieving effective offset compensation without requiring a complex monolithic correction circuit.
Solution Approach 2:
The tracking circuits continuously monitor and track the input offset voltages of the transistor pairs in advance, maintaining ready-to-use compensation signals. When a transistor pair is selected, the corresponding compensation signal is already prepared and can be immediately applied, eliminating delay and ensuring effective offset compensation.
2Adaptability or versatility
If the amplifier transitions between different input transistor pairs, then adaptability to different operating conditions is improved, but offset compensation delay increases
Solution Approach 1:
Multiple tracking circuits continuously track the offset voltages of all input transistor pairs in advance, so that when a transition between transistor pairs occurs, the compensation signal for the newly selected pair is already prepared and can be immediately applied, eliminating transition delay.
Solution Approach 2:
The offset correction system dynamically adapts to different operating conditions by selectively activating the appropriate tracking circuit based on the selected transistor pair. Each tracking circuit is designed to quickly respond to its specific transistor pair's offset characteristics, enabling rapid adaptation during transitions while maintaining overall system versatility.
3Reliability
If conventional filtering is used to remove chopping ripple, then spectral purity can be improved, but the amplifier requires additional filtering components and post-processing
Solution Approach 1:
The chopper frequency is intentionally chosen to be outside the signal bandwidth, converting the potential harmful chopping ripple into a separable frequency component. The tracking circuits generate compensation signals that specifically target and cancel the chopping ripple at the chopper frequency, transforming the ripple from a harmful artifact into a controllable and eliminable frequency component.
Solution Approach 2:
The tracking circuits continuously monitor the output signal for chopping ripple components and generate compensating signals that are fed back to cancel the ripple. This feedback mechanism automatically adjusts the compensation signal to maintain spectral purity without requiring additional external filtering components.
Data Source
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AI summary
Chopper amplifiers with tracking of multiple input offsets are disclosed herein. In certain embodiments, a chopper amplifier includes chopper amplifier circuitry including an input chopping circuit, an amplification circuit, and an output chopping circuit electrically connected along a signal path. The amplification circuit includes two or more pairs of input transistors, from which a control circuit chooses a selected pair of input transistors to amplify an input signal. The chopper amplifier further incudes an offset correction circuit that senses the signal path to generate an input offset compensation signal for the amplification circuit. Furthermore, the offset correction circuit separately tracks an input offset of each of the two or more pairs of input transistors.