Fully Differential PGA With Common-Mode Feedback for Low Distortion
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Solution Overview
Problem
Existing fully-differential programmable gain amplifiers require a high number of components and tight tolerances, leading to inefficiencies and increased distortion, particularly due to the nonlinearity of MOSFET switches, and struggle with common-mode rejection and signal interference.
Innovation Solution
A fully-differential programmable gain amplifier design that utilizes a dual multiplying digital-to-analog converter (DAC) and a resistive ladder network with a data latch circuit to control switches, coupled with a current-to-voltage converter and a correction module for common-mode voltage feedback, reducing component count and tolerances while compensating for distortion and interference.
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 fewer operational amplifiers. Specifically, it uses only two operational amplifiers to implement both differential amplification and programmable gain control, whereas traditional configurations require four operational amplifiers. This merging of functions reduces component count and simplifies the circuit while maintaining differential output capability
Solution Approach 2:
The operational amplifiers in the patent perform multiple functions simultaneously. Each operational amplifier is designed to handle both differential signal processing and gain control operations, making the circuit more universal and efficient. This multi-functionality reduces the overall number of components needed in the amplifier circuit
2Adaptability or versatility
If MOSFET switches are used in the amplifier circuit, then the amplifier can provide programmable gain control, but the nonlinearity of MOSFET switches causes distortion
Solution Approach 1:
The patent implements feedback mechanisms to compensate for the nonlinearity of MOSFET switches. By monitoring the output signal and feeding it back to adjust the control voltages of the MOSFETs, the system can correct for distortion caused by switch nonlinearity. This feedback approach maintains programmable gain control while reducing harmful distortion effects
Solution Approach 2:
The patent changes the operating parameters of the MOSFET switches to minimize nonlinearity effects. By carefully controlling the gate-source voltages and ensuring proper biasing conditions, the MOSFETs operate in a more linear region. This parameter optimization allows programmable gain control to function while reducing signal distortion
3Reliability
If component matching is required for efficient operation, then the amplifier can maintain performance, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent designs the circuit to be self-compensating, reducing the need for precise component matching. The operational amplifiers and feedback networks are configured to automatically adjust and balance the differential signals, compensating for component variations. This self-service approach maintains amplifier performance while simplifying manufacturing requirements
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 achieves high common-mode rejection, low distortion, and reduced switching transients, extending bandwidth and minimizing the impact of MOSFET switch nonlinearity, while maintaining efficient amplification with balanced and unbalanced input signals.
Implementation Method 1
a current-to-voltage converter configured to convert a differential input to an output signal
Data Source
Figure 1A
Figure 1B
Figure 1C
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.