Chopped Capacitive PGA Common-Mode Sampling for Faster Response
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Solution Overview
Problem
Capacitive programmable gain amplifiers (PGAs) do not naturally define the common mode voltage at the inputs of a differential amplifier, requiring additional slow circuitry with large resistors to set this voltage, which is inefficient.
Innovation Solution
The PGA architecture includes a differential amplifier with input and feedback capacitors and chop circuits that sample and define the common mode voltage during a sampling phase, allowing for faster response by controlling the chop circuits to match the common mode voltage of the amplifier inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional circuitry with large resistors is used to set the common mode voltage, then the common mode voltage can be defined, but the response time becomes slow
Solution Approach 1:
The patent extracts the common mode voltage definition function from the traditional resistor-based circuit and relocates it to the capacitive feedback network. By taking out the unnecessary resistor-based common mode setting circuitry and using only the essential capacitive elements already present in the PGA, the design achieves fast response time while maintaining proper common mode voltage definition through the capacitive feedback path.
Solution Approach 2:
The capacitive feedback elements in the PGA serve multiple functions: they provide the feedback necessary for amplification and simultaneously define the common mode voltage at the inputs. This multi-functionality eliminates the need for separate resistor-based common mode setting circuitry, achieving both accurate common mode definition and fast response through a single integrated mechanism.
2Reliability
If additional circuitry is added to set the common mode voltage, then the common mode can be matched, but the device complexity increases
Solution Approach 1:
The capacitive feedback network performs dual functions: providing feedback for signal amplification and simultaneously establishing the common mode voltage level. This eliminates the need for separate common mode setting circuitry with large resistors, reducing overall device complexity while achieving proper common mode matching through the existing capacitive elements.
Solution Approach 2:
The patent removes the unnecessary additional circuitry for common mode voltage setting and relies solely on the capacitive feedback path to define the common mode. By extracting and eliminating redundant components, the design achieves common mode matching with simpler circuitry that has fewer elements and lower complexity.
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 approach enables faster definition of the common mode voltage, reducing noise and improving response time by using capacitive sampling and chop circuit control to maintain the common mode voltage during operational phases.
Implementation Method 1
Low noise, low power and high accuracy PGAs can be implemented using a chopped differential amplifier with capacitors as feedback elements
Implementation Method 2
an input chop circuit converts an input DC signal into a square wave
Implementation Method 3
An output chop circuit then demodulates the amplified square wave back to a gained up DC signal
Data Source
AI summary
A programmable gain amplifier (“PGA”) may include a differential amplifier, a pair of input capacitors, a pair of feedback capacitors provided in feedback configuration about the amplifier, a first chop circuit, provided at an input of the PGA and an output of the PGA and a second chop circuit provided at an output of the PGA. The PGA also may include circuit systems to sample voltages across the input capacitors in a sampling phase. The sampled voltages may correspond to a difference between a common mode voltage of input signals to the PGA and a common mode voltage of the differential amplifier. The sampled voltage, thus, defines a common mode voltage at the amplifier's inputs during other phases of operation, when the chop circuits are operational.