High-Gain Amplifier Offset Correction by Double Sampling
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Solution Overview
Problem
High gain amplifiers, such as transimpedance amplifiers, introduce offset voltages due to charge injection from switch capacitor integrators, which overwhelm small input signals, causing non-linearities and reducing the dynamic range of analog to digital converters.
Innovation Solution
Implementing a double sampling process to subtract sample voltages taken from the amplifier output, thereby reducing or eliminating offset voltage before amplification, and correcting it prior to the gain stage to maintain linearity and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a switch capacitor based integrator is used to convert current to voltage, then the transimpedance amplifier can be realized, but an undesirable supply dependent offset voltage is added to the output
Solution Approach 1:
The patent applies preliminary action by performing offset correction before the signal undergoes further amplification. A correction signal is generated that matches the offset voltage characteristics, and this correction is applied to the amplifier output prior to the programmable gain stage, preventing the offset from being amplified along with the signal
Solution Approach 2:
The patent introduces an intermediary correction signal that acts as a mediator to counteract the offset voltage. This correction signal is generated through a process that mirrors the amplifier's operation and is then combined with the amplifier output, effectively canceling the offset component before it reaches subsequent stages
2Object-generated harmful factors
If the offset voltage is reduced or eliminated, then the output signal quality improves, but non-linearities are introduced into the signal, distorting the output
Solution Approach 1:
The patent employs feedback by generating a correction signal that is derived from the same processes that create the offset voltage. The correction signal is continuously adjusted to match the offset characteristics, and when combined with the amplifier output, it cancels the offset while maintaining signal linearity through the feedback mechanism
3Power
If the amplifier uses a very small capacitor to achieve large gain, then the gain requirement is met, but a relatively high offset voltage results as the capacitor is discharged
Solution Approach 1:
The patent extracts the offset voltage component from the amplifier output signal through a separation process. By generating a correction signal that specifically targets the offset component and subtracting it from the total output, the harmful offset is extracted and removed while the useful signal with high gain is preserved
4Power
If the offset voltage is amplified by a succeeding programmable gain stage, then the signal gain is increased, but the output offset becomes significant, reducing dynamic range
Solution Approach 1:
The patent applies preliminary anti-action by introducing a correction signal that counteracts the offset voltage before the programmable gain stage processes the signal. This preemptive correction prevents the offset from being amplified, thereby preserving the dynamic range while still allowing the desired signal amplification to occur
Data Source
AI summary
A method and an apparatus are described for an offset correction in a high gain amplifier. An embodiment of an amplifier circuit includes an amplifier to convert a current signal into a voltage signal, where the amplifier generates an offset voltage in the voltage signal. The amplifier circuit also includes a sampling component coupled with the amplifier, with the sampling component subtracting a first sample of the voltage signal from a second sample of the voltage signal to produce a difference value. The amplifier circuit further includes a gain component coupled with the sampling component to amplify the difference between the first sample and the second sample.