Bias Current Circuit With Temperature-Compensated Variable Resistance
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Solution Overview
Problem
Bias current generation circuits in electronic systems face instability due to temperature variations affecting the resistance of internal load resistors, leading to fluctuations in bias current despite stable control voltages.
Innovation Solution
A bias current generation circuit comprising an operational amplifier, an output transistor, and a variable resistive circuit, where the operational amplifier generates a driving voltage from input and feedback voltages with zero-temperature coefficients, and the variable resistive circuit, composed of series resistors and switch transistors, adjusts its total resistance to maintain a zero-temperature coefficient, ensuring the bias current remains stable across temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bias current generation circuit uses an internal load resistor, then the circuit can generate bias current, but the resistance of the internal load resistor varies with temperature causing the bias current to become unstable
Solution Approach 1:
The patent implements a feedback mechanism where the operational amplifier continuously monitors the voltage across the load resistor and adjusts the driving voltage to the output transistor accordingly. This closed-loop feedback system compensates for temperature-induced resistance changes in the load resistor, maintaining stable bias current output despite temperature variations.
Solution Approach 2:
The patent utilizes the temperature-dependent characteristics of the load resistor and compensates by dynamically adjusting the driving voltage parameter through the operational amplifier. By changing the voltage parameter in response to temperature-induced resistance changes, the system maintains constant bias current despite parameter variations in the load resistor.
Data Source
AI summary
The present invention discloses a bias current generation circuit. An operation amplifier compares an input voltage having a zero-temperature coefficient and a feedback voltage to generate a driving voltage. An output transistor generates a bias current according to the driving voltage. A variable resistive circuit is electrically coupled to the output transistor through a feedback node to generate the feedback voltage according to the bias current and includes series-coupled resistors and switch transistors. Each of the resistors has a resistance having a positive temperature coefficient and includes a current input terminal and a current output terminal. Each of the switch transistors is electrically coupled between the current output terminal of one of the resistors and a ground terminal. One of the switch transistors turns on according to a control voltage variable according to the temperature variation to enable resistors to generate the resistance having a negative temperature coefficient.