Sub-Threshold Parallel Amplifier for Third-Order Distortion Cancellation
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Solution Overview
Problem
Ultra low power (ULP) applications face significant third order derivative distortion due to nonlinear transfer function characteristics of amplifiers, leading to limited sensitivity and dynamic range in the presence of blockers.
Innovation Solution
A method involving two amplifiers, one with a positive third derivative transfer function and another with a negative third derivative transfer function, operating in the sub-threshold region, are arranged in parallel to cancel out third order distortions by generating amplified signals in opposite phases, with adjustable bias currents to ensure equal amplitude and opposite phase distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a single amplifier operates in the sub-threshold region to achieve ultra low power consumption, then current consumption is reduced, but third order derivative distortion increases due to nonlinear transfer function characteristics
Solution Approach 1:
The patent combines two amplifiers operating in the sub-threshold region with opposite third derivative signs (one positive, one negative) to achieve distortion cancellation. The amplifiers are merged in parallel configuration where their output signals are summed, allowing the third order distortion components to cancel each other while maintaining ultra low power operation. This merging approach resolves the contradiction by achieving both low power consumption and reduced distortion through cooperative operation of multiple devices.
Solution Approach 2:
The patent employs a composite amplifier structure consisting of two distinct amplifier circuits with complementary characteristics. One amplifier is designed with a positive third derivative transfer function while the other has a negative third derivative, creating a composite system where the harmful third order distortions cancel out. This composite approach allows the system to maintain the benefits of sub-threshold operation (ultra low power) while eliminating the primary disadvantage (high distortion).
2Object-generated harmful factors
If amplifier bias current is increased to reduce distortion, then third order derivative distortion decreases, but current consumption increases
Solution Approach 1:
The patent converts the harmful third order distortion generated by each individual amplifier into a beneficial cancellation mechanism. By designing one amplifier with positive third derivative and another with negative third derivative, both operating at ultra low currents, the distortions that would normally be harmful are instead made to cancel each other out. This approach allows distortion reduction without requiring increased current consumption, as the harm is converted into a self-correcting mechanism.
Solution Approach 2:
The patent changes the operating parameters of the amplifiers by adjusting their bias currents to achieve equal magnitude but opposite sign third derivatives. The bias current of the second amplifier is specifically tuned so that its third order distortion component matches in amplitude but opposes in phase to the first amplifier's distortion. This parameter adjustment enables distortion cancellation while maintaining ultra low power operation, resolving the contradiction between distortion reduction and power consumption.
3Device complexity
If a single amplifier is used to simplify the circuit, then device complexity is reduced, but sensitivity and dynamic range are limited due to distortion
Solution Approach 1:
The patent merges two amplifiers in parallel with a common load, combining their outputs to achieve distortion cancellation. While this increases circuit complexity compared to a single amplifier, the merging provides the benefit of improved sensitivity and dynamic range through distortion reduction. The combined structure allows the system to overcome the limitations of individual amplifiers operating in the sub-threshold region.
Solution Approach 2:
The patent employs additional amplifier components and biasing circuitry to achieve distortion cancellation, accepting increased device complexity as a trade-off for significantly improved performance. The extra components are necessary to generate the opposing third derivative characteristic and enable the cancellation mechanism, prioritizing reliability and performance over minimal circuit complexity.
Data Source
AI summary
An apparatus and method for the cancellation of third order derivative distortion for ultra low power (ULP) applications are disclosed involving a first amplifier connected in parallel with a second amplifier for amplifying a received signal. The first amplifier includes at least one transistor operating in the sub-threshold region such that the first amplifier possesses a positive third derivative of a transfer function of the first amplifier, which generates a first amplified signal having in phase third order distortions. The second amplifier includes at least one differential pair of transistors operating in the sub-threshold region such that the second amplifier possesses a negative third derivative of a transfer function of the second amplifier, which generates a second amplified signal having in opposite phase third order distortions. The first and second amplified output signals are combined resulting in cancellation of third order distortions in the combined amplified signal.