Chopper Amplifier Output Switching for Low IMD
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Solution Overview
Problem
Chopper amplifiers suffer from intermodulation distortion (IMD) due to finite amplifier delay and limited bandwidth, leading to discontinuous output current and significant distortion, especially when input frequencies are near multiples of the chopping frequency, which complicates filtering and increases noise floor.
Innovation Solution
Incorporating a distortion compensation channel in parallel with the main signal channel, along with output selection switches to maintain continuous output current, which compensates for IMD by filling in missing current or using settled channel outputs, thereby reducing distortion and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chopper circuitry is used to compensate for input offset voltage, then offset voltage is separated in frequency and can be filtered, but intermodulation distortion increases due to finite amplifier delay and limited bandwidth
Solution Approach 1:
The amplifier is divided into multiple parallel channels: a main signal channel that processes the input signal through chopping and amplification, and distortion compensation channels that specifically address IMD. This segmentation allows independent optimization of each channel's function while working together to achieve both offset compensation and distortion reduction.
Solution Approach 2:
Distortion compensation channels act as intermediaries that generate compensation signals to counteract the IMD produced by the main signal channel. These intermediate compensation signals are combined with the main channel output to eliminate the harmful intermodulation distortion while preserving the beneficial offset compensation.
2Object-generated harmful factors
If amplifier bandwidth is increased to reduce intermodulation distortion, then distortion decreases, but device complexity and power consumption increase
Solution Approach 1:
Rather than increasing the bandwidth of a single amplifier, the system segments the signal processing into multiple parallel channels with moderate bandwidth requirements. The distortion compensation channels operate in parallel to address IMD without requiring any single channel to have excessive bandwidth, thus maintaining manageable device complexity.
Solution Approach 2:
The distortion compensation channels use simplified versions or copies of the main signal channel architecture, replicated and configured to generate compensation signals. This copying approach allows the system to address distortion without requiring complex high-bandwidth amplifier designs, as the compensation channels can use simpler, lower-bandwidth implementations.
3Object-generated harmful factors
If distortion compensation channels are added in parallel, then intermodulation distortion is reduced, but device complexity increases
Solution Approach 1:
The distortion compensation channels are designed to perform multiple functions: they compensate for IMD, maintain continuous output current, and can be integrated with the main signal channel architecture. This multi-functionality reduces the need for additional separate circuits, thereby limiting the increase in device complexity while achieving distortion reduction.
Solution Approach 2:
The distortion compensation channels are merged with the main signal channel at the output stage, where their compensation signals are combined with the main channel output. This merging approach allows the system to benefit from multiple channels for distortion compensation while consolidating the overall structure to minimize complexity increases.
Data Source
AI summary
Chopper amplifiers with low intermodulation distortion (IMD) are provided. To compensate for IMD, at least one distortion compensation channel is included in parallel with chopper amplifier circuitry of a main signal channel. Additionally, output selection switches are included for selecting between the output of the main signal path and the distortional compensation channel(s) over time to maintain the output current continuous. Such IMD compensation can be realized by filling in missing current of the main signal channel using the distortion compensation channel(s), or by using channel outputs only when they have settled current.