FBDDA Amplifier Switching for Low-Noise High-Linearity Operation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fully Balanced Differential Difference Amplifiers (FBDDA) suffer from high total harmonic distortion (THD) at high input signal levels due to unbalanced differential pairs, leading to linearity deterioration, and existing solutions either increase noise or require excessive current consumption.
Innovation Solution
The FBDDA amplifier incorporates resistive-degeneration groups coupled with by-pass switches controlled by signals VCTRL1 and VCTRL2, which are activated only for high input signal values, allowing the amplifier to operate in different conditions to maintain linearity without excessive noise or current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If degeneration resistors are coupled to each differential-input pair to improve linearity, then total harmonic distortion is reduced, but noise increases
Solution Approach 1:
The patent implements dynamic switching of degeneration resistors based on input signal amplitude. For small signals, the resistors are bypassed to maintain low noise. For large signals, the resistors are activated to improve linearity and reduce harmonic distortion. This dynamic adaptation resolves the contradiction by providing different impedance conditions optimal for different signal levels.
Solution Approach 2:
The patent changes the effective resistance value at the differential input pairs based on signal conditions. By switching between bypassed and active states, the degeneration resistance parameter is dynamically adjusted to optimize performance for either low noise (small signals) or high linearity (large signals).
2Manufacturing precision
If dynamic-biasing circuits are used to vary bias current with input signal, then linearity is improved, but current consumption increases excessively
Solution Approach 1:
The patent dynamically switches the biasing configuration based on input signal amplitude. For small signals, a first biasing configuration is used that minimizes current consumption. For large signals, a second biasing configuration is activated that provides optimal linearity. This dynamic switching avoids the excessive current consumption of continuously active dynamic-biasing circuits while maintaining linearity when needed.
Solution Approach 2:
The bias current parameter is dynamically adjusted based on signal conditions. The patent switches between different bias current levels - a lower current for small signals to save power, and an optimized current for large signals to maintain linearity. This parameter adaptation resolves the contradiction between linearity and current consumption.
3Reliability
If the FBDDA amplifier operates without closed-loop configuration, then input impedance remains high, but linearity deteriorates at high signal levels
Solution Approach 1:
The patent dynamically modifies the amplifier's operating characteristics based on signal amplitude. For small signals, the amplifier operates in a high-impedance mode without closed-loop feedback. For large signals, degeneration resistors are activated to provide local feedback that improves linearity while maintaining the overall high input impedance characteristic of the FBDDA architecture.
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A FBDDA amplifier (10) comprising: a first differential input stage (1a, 1b), which receives an input voltage (Vin); a second differential input stage (1c, 1d), which receives a common-mode voltage (VCM); a first resistive-degeneration group (12) coupled to the first differential input; a second resistive-degeneration group (16) coupled to the second differential input; a differential output stage, generating an output voltage; a first switch (14) coupled in parallel to the first resistive-degeneration group (12); and a second switch (18) coupled in parallel to the second resistive-degeneration group (16). The first and second switches (14, 18) are driven into the closed state when the voltage input (Vin) assumes a first value such that said first input stage operates in the linear region, and are driven into the open state when the voltage input (Vin) assumes a second value, higher than the first value, such that the first input stage operates in a non-linear region.