AC-Coupled Amplifier Circuit for Beyond-Supply Signal Range
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Solution Overview
Problem
Single supply integrated circuits face challenges in processing received voltages that exceed the supply voltage, leading to electrostatic discharge protection issues and reduced amplifier fidelity due to lack of headroom.
Innovation Solution
A high impedance, low-noise amplifier circuit with AC-coupling and level-shifting capabilities, utilizing capacitors and switches to pre-charge and sample signals, and incorporating auto-zero or chop operations to mitigate noise and offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single supply integrated circuit is used to process voltages exceeding the supply voltage, then the circuit can handle higher voltage signals, but electrostatic discharge protection issues occur and amplifier fidelity deteriorates due to lack of headroom
Solution Approach 1:
The patent introduces an intermediary circuit comprising coupling capacitors and level-shifting circuitry between the high-voltage signal source and the amplifier. This intermediary circuit translates the high-voltage signal to the amplifier's supply voltage range while maintaining signal integrity, thus protecting the amplifier from voltage excursions that would cause electrostatic discharge damage and fidelity loss.
Solution Approach 2:
The coupling capacitors are pre-charged to specific voltages before signal transmission begins. This preliminary charging establishes the correct DC operating point and prevents sudden voltage transients that could trigger electrostatic discharge protection mechanisms or exceed the amplifier's headroom, thereby maintaining reliable operation throughout signal processing.
2Adaptability or versatility
If AC-coupling capacitors are used to level-shift signals, then signals beyond supply range can be processed, but additional circuit components and complexity are introduced
Solution Approach 1:
The coupling capacitors serve multiple functions simultaneously: they perform AC-coupling to block DC offsets, level-shift the signal to the appropriate voltage range, and provide impedance matching. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall circuit complexity despite the expanded signal processing 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
Enables amplification of signals beyond the supply range with high linearity and low noise performance, suitable for various applications including interface circuits and sensor systems.
Implementation Method 1
charging first and second capacitors to first and second bias voltages. The first capacitor is coupled to a first input of an amplifier circuit, which has a second input and an output. The second capacitor is coupled to the second input.
Implementation Method 2
the output of the amplifier is coupled to the second input through the second capacitor to level shift a feedback signal according to the second bias voltage
Data Source
AI summary
A method of operating an amplifier circuit having a pre-charge phase and a sample/conversion phase includes, during a pre-charge phase, charging first and second capacitors to first and second bias voltages. The first capacitor is coupled to a first input of an amplifier circuit, which has a second input and an output. The second capacitor is coupled to the second input. During a sample/conversion phase, the first input of the amplifier circuit is coupled to an input signal through the first capacitor to level-shift the input signal according to the first bias voltage and the output of the amplifier is coupled to the second input through the second capacitor to level shift a feedback signal according to the second bias voltage.