Op-Amp Offset Compensation With Threshold Precharge Calibration
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Solution Overview
Problem
The calibration of operational amplifiers in integrated circuits is slow due to long transition times between voltage levels caused by low output current and parasitic capacitances, delaying the start-up phase of the integrated circuit.
Innovation Solution
A calibration method that couples the negative and positive inputs of the amplifier to the same voltage level, using a current-to-voltage converter to generate a control voltage for rapid offset compensation, and a trigger element to automatically detect transition and generate a compensation signal gradually clocked by a clock signal, reducing the duration of the calibration phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the amplifier output current is kept low to minimize power consumption and avoid disturbing the output node voltage, then the transition time between voltage levels becomes excessively long due to slow charging of parasitic capacitances
Solution Approach 1:
The patent applies preliminary action by pre-charging the parasitic capacitances at the output node to the threshold voltage Vth through a switching circuit before the actual transition. This preparation eliminates the need for slow charging during the transition itself, allowing the amplifier to switch states rapidly without requiring high output current during the transition period.
Solution Approach 2:
The patent employs periodic action through a switching circuit that alternates between charging the parasitic capacitances to the threshold voltage and allowing the amplifier to transition. This periodic pre-charging enables fast transitions while maintaining low average power consumption, as the high current flows only briefly during periodic pre-charge cycles rather than continuously.
2Extent of automation
If a threshold comparison method is used to detect the transition point for offset compensation, then the calibration can be automated, but the long transition time delays the overall calibration process
Solution Approach 1:
The switching circuit performs preliminary action by pre-charging the parasitic capacitances to the threshold voltage Vth before the amplifier transition occurs. This eliminates the need to wait for slow natural charging during transition detection, enabling the threshold comparison method to detect transitions rapidly and maintain automated calibration without time delays.
3Measurement precision
If the inputs are short-circuited during calibration to eliminate external voltage deviations, then only the offset voltage affects the output, but the calibration process becomes time-consuming due to slow transition detection
Solution Approach 1:
The switching circuit applies preliminary action by pre-charging the parasitic capacitances to the threshold voltage Vth before offset compensation transitions. This enables rapid detection of transition points during calibration, maintaining precise offset voltage measurement while significantly reducing the overall calibration duration by eliminating slow charging delays.
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 method significantly reduces the calibration time by eliminating the need for charging parasitic capacitances with low-intensity currents and allows for quick detection and compensation of internal voltage offsets, thereby accelerating the start-up of the integrated circuit.
Implementation Method 1
biasing the output of the first amplifier to a threshold voltage, with a current-to-voltage converter, and the generation of a control voltage with the current-to-voltage converter comprising the sum of the threshold voltage and a voltage conversion of the comparison current
Implementation Method 2
The transition time between the voltage levels generated by the first amplifier is long, due to the output current of the first amplifier being very low to produce an output voltage by capacitive charge on the output node. The capacitive value on the output node can, for example, originate from parasitic capacitances in the output stage of the first amplifier
Data Source
AI summary
An internal voltage offset between a positive input and a negative input of a first operational amplifier is compensated. The negative input and the positive input of the first operational amplifier are coupled at the same voltage level. A comparison current generated at an output of the first operational amplifier has a sign that is representative of a sign of the internal voltage offset. The output of the first operational amplifier is biased to a threshold voltage using a current-to-voltage converter. A control voltage is generated from a sum of the threshold voltage and a voltage conversion of the comparison current. Compensation for the internal voltage offset between the positive and negative inputs of the first operational amplifier is made dependent on the control voltage.