Chopper-Stabilized Amplifier Layout With Lower Input Bias Current
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Solution Overview
Problem
Chopper stabilized amplifiers have complex wiring and large circuit areas due to the need for multiple correction amplifiers, which complicates the cancellation of input offset voltage and results in significant input bias currents.
Innovation Solution
A simplified chopper stabilized amplifier configuration that eliminates the need for capacitors between selectors and gm amplifiers, using a full differential second gm amplifier with a depletion-type differential input pair and a common mode feedback circuit to reduce circuit area and input offset current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple correction amplifiers are used to cancel offset voltage, then the offset voltage cancellation is improved, but the device complexity and circuit area increase significantly
Solution Approach 1:
The patent merges the functions of multiple correction amplifiers into a single correction amplifier by integrating offset voltage sampling and correction functions. The correction amplifier includes a sampling switch that captures offset voltage during a first phase and injects it back during a second phase, eliminating the need for separate correction amplifiers while maintaining offset cancellation capability.
Solution Approach 2:
The correction amplifier is designed to perform multiple functions: it acts as both a voltage amplifier during normal operation and an offset voltage sampler during the first phase. The same amplifier core is used for both signal amplification and offset correction, reducing the total number of components required.
2Measurement precision
If multiple correction amplifiers and switches are used, then the offset voltage cancellation is improved, but the circuit area becomes large
Solution Approach 1:
The patent combines offset sampling capacitors and correction functionality into a single integrated correction amplifier unit. The sampling capacitors are integrated within the correction amplifier circuit rather than being separate components, significantly reducing the overall circuit area while maintaining offset cancellation capability.
3Adaptability or versatility
If capacitors are added between selectors and gm amplifiers, then the circuit functionality is improved, but the input bias current increases significantly
Solution Approach 1:
The patent extracts and eliminates the capacitors between selectors and gm amplifiers from the circuit configuration. By removing these capacitors, the source of significant input bias current is eliminated, while the essential chopper stabilization functionality is maintained through the integrated correction amplifier's sampling and injection mechanism.
Data Source
AI summary
There is provided a chopper stabilized amplifier with an input bias current reduced. The chopper stabilized amplifier includes a main amplifier and a correction circuit. The correction circuit includes a second gm amplifier of a full differential type. A first selector and the second gm amplifier are coupled to each other without DC blocking capacitors. The differential input state of the second gm amplifier is configured with a depletion-type transistor.