Differential Input Pair Tail-Current Modulation for Linearity
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Solution Overview
Problem
Fully differential amplifiers experience distortion at large differential input voltages due to non-linear transconductance of input transistors, leading to non-linear output current behavior.
Innovation Solution
Incorporating a current modulator and absolute value circuit that modulates the source current based on differential input signals, ensuring improved linearity by varying the conductance of transistors and adjusting the output current profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fully differential amplifier uses a current mirror to control tail current, then the amplifier can operate with a stable bias current, but the transconductance becomes non-linear at large differential input voltages causing output distortion
Solution Approach 1:
The patent applies dynamics by making the tail current dynamic rather than fixed. The current mirror's reference current is modulated by the differential input voltage through a transconductance stage, causing the tail current to automatically adjust its magnitude based on the input signal level. This dynamic tail current compensates for the non-linear transconductance of the input transistors, maintaining linear output current over a wide differential input voltage range while preserving bias stability through the current mirror's feedback mechanism.
2Adaptability or versatility
If the amplifier operates over a large range of differential input voltages, then the amplifier can handle larger signals, but the non-linear transconductance causes increased distortion
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the tail current magnitude as a function of the differential input voltage. The current mirror's reference current parameter is modulated by the input voltage through a transconductance stage, causing the tail current to increase with larger differential inputs. This parameter modulation compensates for the inherent non-linearity of the input transistors, enabling linear operation over an extended input voltage range from -Vdd to +Vdd.
3Power
If the transconductance is increased to improve gain, then the amplifier gain increases, but the non-linear behavior of transistors causes greater distortion at large input voltages
Solution Approach 1:
The patent applies feedback through the current mirror configuration where the output current is fed back to modulate the reference current of the current mirror. The differential input voltage controls a transconductance stage that adjusts the tail current based on the output current level, creating a feedback loop that linearizes the overall transfer function. This feedback mechanism allows high gain operation while maintaining linearity by automatically adjusting the bias conditions based on the signal level.
Data Source
AI summary
The invention is directed to an amplifier including an absolute value circuit. The absolute value circuit may be driven by differential potentials and may include a first pair of transistors modulating a tail current of the amplifier when a differential input voltage goes high, and a second pair of transistors modulating the tail current of the amplifier when a differential input voltage goes low.