Compensated Source-Follower Current Source
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Solution Overview
Problem
Source-follower based current sources face instability due to temperature and process variations, causing inaccuracies in generated reference currents as the voltage drop across main transistors changes.
Innovation Solution
Incorporating a voltage compensation semiconductor device, such as an auxiliary transistor, that matches the main transistor in current density and is biased to provide an offset voltage that pre-compensates for the voltage drop across temperature and process variations, ensuring a stable reference current output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a source-follower based current source is used to generate reference current, then the circuit complexity is reduced and cost is lowered, but the current accuracy deteriorates due to voltage drop variations with temperature and process
Solution Approach 1:
The patent applies preliminary action by introducing a compensation transistor that pre-adjusts the voltage drop across the main transistor. The compensation transistor is biased to generate a voltage that counteracts the expected voltage drop variations of the main transistor due to temperature and process changes, thereby pre-compensating for accuracy errors before they affect the reference current output.
Solution Approach 2:
The patent utilizes parameter changes by exploiting the temperature and process dependence of transistor threshold voltages. The compensation transistor is designed with specific sizing ratios relative to the main transistor, and its bias conditions are adjusted so that its voltage characteristics change in opposition to the main transistor's voltage drop, thereby compensating for parameter variations.
2Measurement precision
If bias currents are increased to compensate for voltage drop variations, then the current accuracy is improved, but the power consumption increases
Solution Approach 1:
The patent applies partial action by using a compensation transistor that provides just enough voltage compensation to counteract the main transistor's voltage drop variations. The compensation is designed to be sufficient for accuracy but not excessive, and the bias currents are set to the minimum level needed to achieve the required compensation, avoiding unnecessary power consumption.
Data Source
AI summary
An electronic circuit for current generation includes a source-follower based current source and a voltage compensation semiconductor device. The source-follower based current source is configured to output a reference current, the current source including a main transistor which is configured to derive the reference current from a reference voltage, wherein the main transistor has a voltage drop that varies with temperature and process variations. The voltage compensation semiconductor device is configured to be biased with bias currents that increase the reference voltage provided to the main transistor by an offset voltage that matches the voltage drop of the main transistor across at least part of the temperature and process variations, thereby pre-compensating for the voltage drop of the main transistor.