Op-Amp Trim Offset Circuit Using DAC Current Switching
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Solution Overview
Problem
Operational amplifiers often experience inaccuracies due to offsets in their input stages, which can lead to voltage offsets and inefficiencies, particularly in low-power applications where additional trimming circuitry increases power consumption.
Innovation Solution
A digital-to-analog conversion (DAC) circuit with a reference voltage source and drain switching elements is used to selectively couple adjustment currents to the operational amplifier, allowing for precise trim current adjustments that reduce power consumption to 100 nanoamps or lower.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional trimming circuitry is added to correct input stage offsets, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The patent changes the operational parameters of the trimming circuit by using digital control signals to selectively activate specific transistor pairs based on the required trim amount. This allows the circuit to operate with minimal power consumption by only activating the necessary components rather than maintaining a continuous power-hungry trimming circuit.
Solution Approach 2:
The trimming circuit is made dynamic through the use of digital control signals that can selectively enable or disable specific transistor pairs. This dynamic control allows the circuit to adapt its power consumption based on the actual trimming requirements, consuming power only when and where needed rather than continuously.
2Manufacturing precision
If digitally trimmed op-amps with additional circuitry are employed, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The trimming circuit is segmented into multiple independent transistor pairs, each controlled by a separate digital control signal. This segmentation allows for precise control of individual trim elements while keeping each segment simple and manageable, reducing overall circuit complexity compared to a monolithic trimming circuit.
Solution Approach 2:
The transistor pairs in the trimming circuit are designed to serve multiple functions: they provide both the trimming capability and the digital control interface. This multi-functionality reduces the need for separate control circuitry, thereby reducing overall device complexity while maintaining precise offset trimming capability.
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 corrects input stage offsets in operational amplifiers while minimizing power dissipation, enhancing accuracy and reducing current draw, thereby improving performance in low-power environments.
Implementation Method 1
each pair among the plurality of transistor pairs is configured to provide portions of adjustment currents for an operational amplifier based at least on the set of reference voltages and sizing among transistors of each pair
Implementation Method 2
drain switching elements coupled to drain terminals of the transistors of each pair and configured to selectively couple one or more of the portions of the adjustment currents to the operational amplifier in accordance with digital trim codes
Data Source
AI summary
Enhanced operational amplifier trim circuitry and techniques are presented herein. In one implementation, a circuit includes a reference circuit configured to produce a set of reference voltages, and a digital-to-analog conversion (DAC) circuit. The DAC circuit comprises a plurality of transistor pairs, where each pair among the plurality of transistor pairs is configured to provide portions of adjustment currents for an operational amplifier based at least on the set of reference voltages and sizing among transistors of each pair. The circuit also includes drain switching elements coupled to drain terminals of the transistors of each pair and configured to selectively couple one or more of the portions of the adjustment currents to the operational amplifier in accordance with digital trim codes.