Variable Gain Amplifier Feedback Circuit for dB-Linear Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing variable gain amplifiers (VGAs) fail to provide a smooth, linear gain control curve in db/volts, leading to signal distortion and noise modulation due to bumps and ripples in the gain curve, and are often temperature-sensitive and prone to manufacturing variations.
Innovation Solution
A db-linear process-independent variable gain amplifier design utilizing a transconductance circuit with a gate voltage control circuit that includes a feedback loop and matched MOSFET devices to achieve a substantially linear gain control curve, insensitive to temperature and manufacturing variations, using a feedback loop with a bipolar junction transistor and op amp to modulate the transconductance of MOSFETs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional VGA circuit designs are used, then variable gain amplification is achieved, but the gain curve exhibits bumps and ripples that deviate from a constant slope
Solution Approach 1:
The patent employs feedback mechanisms where the output signal is fed back to the input through carefully designed feedback networks. This feedback loop continuously adjusts the gain to maintain a linear db-volt relationship, correcting deviations and eliminating bumps and ripples in the gain curve that would otherwise cause signal distortion.
Solution Approach 2:
The invention changes the operating parameters of the VGA circuit by using multiple gain stages with different gain values that are switched or blended based on the control voltage level. This parameter transformation approach converts a non-linear gain characteristic into a linear db-volt relationship across the entire operating range.
2Ease of operation
If approximated log linear gain curves with bumps and ripples are used, then variable gain amplification is provided, but control line noise modulates the signal in an undesirable manner
Solution Approach 1:
The feedback mechanism continuously monitors the actual gain and adjusts it to maintain linearity, which also stabilizes the operating point against noise variations. This reduces the modulation effect of control line noise on the output signal.
Solution Approach 2:
The circuit design incorporates compensation elements that anticipate and counteract the effects of control line noise before it can significantly modulate the signal. By pre-adjusting the gain characteristics to be more linear, the circuit reduces the sensitivity to control voltage variations and associated noise.
3Power
If prior VGA device designs are used, then amplification is achieved, but the devices are temperature sensitive over a given temperature range
Solution Approach 1:
The feedback loop compensates for temperature-induced variations in transistor parameters by continuously adjusting the gain to maintain the desired linear db-volt relationship. This feedback mechanism counteracts the effects of temperature drift on the amplification characteristics.
Solution Approach 2:
The circuit uses temperature-compensated biasing schemes and selects operating points that are less sensitive to temperature variations. By changing the operating parameters and using multiple gain stages with complementary temperature characteristics, the overall temperature sensitivity is reduced.
4Productivity
If conventional VGA designs are used, then variable gain is provided, but the devices are not able to provide repeatable gain on a constant basis due to manufacturing process variations
Solution Approach 1:
The feedback mechanism compensates for manufacturing variations by continuously adjusting the gain to match the target linear db-volt relationship. This closed-loop approach reduces sensitivity to component tolerances and process variations, improving repeatability across different devices and production batches.
Solution Approach 2:
The design uses multiple gain stages with parameters that are less sensitive to manufacturing variations. By transforming the gain control into a logarithmic domain and using ratio-based circuits, the design achieves better immunity to absolute parameter variations while maintaining precise relative control.
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
The solution provides a repeatable, linear gain curve over a wide temperature range with low noise and high dynamic range, maintaining signal fidelity and eliminating the need for post-production trimming or external gain normalization.
Implementation Method 1
The gate control voltage modulates the transconductance of the first MOSFET and the first resistance
Implementation Method 2
The amplifier or attenuator circuit comprises a transconductance circuit controlled, to some degree, by a gate voltage control circuit. The gate voltage control circuit comprises a first MOSFET device having a gate, a source and drain. The gate voltage control circuit further comprises a feedback loop such that the feedback loop comprises a feedback bipolar junction transistor (BJT)
Data Source
AI summary
An amplifier is provided with continuously-variable analog control that exhibits a highly linear gain control curve in db/volts, while preserving high dynamic range, low third order distortion, and low noise. This amplifier has a control mechanism that preserves a varied linear or log linear curve over a wide range and is inherently insensitive to process variations thereby allowing more accurate gain control and higher signal fidelity for amplifying high dynamic range signals.