Fully Differential PGA Circuit With Common-Mode Distortion Compensation
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Solution Overview
Problem
Existing differential programmable gain amplifiers require a high number of components and tight tolerances, leading to inefficiencies and distortion, particularly due to the nonlinearity of MOSFET switches, and struggle with common-mode rejection and control signal interference.
Innovation Solution
A fully-differential programmable gain amplifier design that utilizes a dual multiplying digital-to-analog converter (DAC) and a single operational amplifier, with a resistive ladder network and data latch circuit to control switches, and a current-to-voltage converter to produce differential outputs, while incorporating a correction module for common-mode rejection and distortion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional differential programmable gain amplifier configuration is used, then the amplifier can provide differential output, but it requires an undesirably high number of components and high tolerances
Solution Approach 1:
The patent combines multiple functions into a single operational amplifier. The differential amplifier and current-to-voltage converters are integrated into one op-amp circuit, eliminating the need for separate components. This merging reduces component count from five active components to one, while maintaining differential output capability and reducing matching tolerance requirements.
Solution Approach 2:
The single operational amplifier performs multiple functions simultaneously: it acts as a differential amplifier, performs current-to-voltage conversion for both differential inputs, and provides the required gain. This multi-functionality eliminates the need for separate dedicated components for each function, resolving the contradiction between component count and functionality.
2Reliability
If multiple amplifying circuits are used in the signal path, then differential output can be achieved, but the device complexity and number of components increase
Solution Approach 1:
The patent merges the differential amplification function and current-to-voltage conversion functions into a single operational amplifier circuit. The op-amp simultaneously processes both differential inputs and produces differential outputs, eliminating the need for multiple separate amplifying circuits while maintaining output quality.
3Adaptability or versatility
If MOSFET switches are used in the amplifier, then programmable gain is achieved, but nonlinearity of MOSFET switches causes distortion
Solution Approach 1:
The patent employs feedback mechanisms where the single operational amplifier uses its high gain to automatically correct for MOSFET nonlinearity. The feedback loop senses the actual output and adjusts the input signals to compensate for distortion introduced by the MOSFET switches, thereby maintaining signal fidelity while preserving programmable gain functionality.
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 design reduces component requirements, minimizes distortion, and enhances common-mode rejection, achieving high efficiency and low interference by compensating for MOSFET switch nonlinearity and maintaining high bandwidth.
Implementation Method 1
a current-to-voltage converter to convert the differential input from the programmable gain module to a differential output
Data Source
AI summary
A programmable a fully-differential programmable gain amplifier for reducing distortion, switching transients and interference, and improving bandwidth. In one embodiment, the amplifier includes a programmable gain module, an amplifier coupled to the current mode outputs and a data latch circuit of the programmable gain module, the amplifier configured to apply common mode voltage to the data latch circuit, and a current-to-voltage converter. In one embodiment, the fully-differential programmable gain amplifier controls distortion and switching interference during amplification by sensing common mode signals to produce an error signal, and applying the resulting error signal to the programmable gain module for multiplying digital to analog conversion. Components of the fully-differential programmable gain amplifier provide compensation of distortion caused by nonlinearity of device switches and switch resistance, and can include a floating supply, galvanic isolation of control signals and a common mode voltage controller.