Dual-loop transmit noise cancellation circuit
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Solution Overview
Problem
In duplex wireless communication systems, transmitter noise poses a significant challenge as it interferes with the receiver's ability to detect incoming signals, and existing solutions like circuit design modifications or filtering are expensive and require high power consumption or large, costly filters.
Innovation Solution
A transmitter circuit with dual feedback loops and local oscillators is used to estimate and filter out transmitter noise and distortion, employing mixers, filters, and a plant to generate a noise-canceled transmit signal, which can be applied universally across frequency bands without the need for separate filters for each band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If circuit design modifications are used to reduce transmitter noise, then transmitter noise is reduced, but power consumption increases and device size increases
Solution Approach 1:
The patent implements a feedback-based noise cancellation system where the transmit signal is fed back through a model of the power amplifier and associated circuits. The feedback path includes a mixer that downconverts the signal to baseband, followed by processing that generates an estimate of the noise and distortion. This estimated noise is then subtracted from the received signal, creating a closed-loop system that actively cancels transmitter noise without requiring additional power-consuming hardware modifications.
2Object-generated harmful factors
If circuit design modifications are used to reduce transmitter noise, then transmitter noise is reduced, but device size increases
Solution Approach 1:
The patent creates a computational model (copy) of the power amplifier and associated transmit circuits that replicates their noise and distortion characteristics. Instead of physically modifying the circuits to reduce noise, the system uses digital signal processing to create and subtract a copy of the expected noise signal. This approach eliminates the need for additional physical noise-reduction components, maintaining a compact device form factor.
3Object-generated harmful factors
If filters are used to reduce transmitter noise, then transmitter noise is reduced, but filter size and cost increase
Solution Approach 1:
The patent replaces physical filtering mechanisms with a signal processing approach. Instead of using hardware filters to remove transmitter noise from the received signal, the system uses digital signal processing to estimate and subtract the noise component. The noise estimation is achieved by processing the feedback signal through mixers and digital filters, then subtracting the result from the received signal. This substitution of mechanical/filter-based solutions with signal processing eliminates the need for large, costly physical filters.
4Object-generated harmful factors
If separate filters are used for each frequency band, then noise filtering is effective, but device complexity and cost increase
Solution Approach 1:
The patent implements a universal noise cancellation architecture that works across multiple frequency bands without requiring separate filter configurations for each band. The feedback-based system processes the transmit signal through a model that captures the essential noise and distortion characteristics, then subtracts the estimated noise from the received signal. This approach provides frequency-band-independent noise cancellation, eliminating the need for multiple separate filters and reducing overall system complexity.
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 approach effectively reduces transmitter noise and distortion, improving signal fidelity and reducing system filtering requirements, making it a cost-effective solution for various wireless communication systems.
Implementation Method 1
a first local oscillator that generates a first frequency equal to a duplex frequency... a second local oscillator that generates a second frequency equal to a receive frequency
Implementation Method 2
a first mixer that combines the first frequency with a first input signal... a second mixer that combines the second frequency with a transmit signal
Data Source
AI summary
A transmitter circuit is described. The transmitter circuit includes a first local oscillator that generates a first frequency equal to a duplex frequency. The transmitter circuit also includes a second local oscillator that generates a second frequency equal to a receive frequency. The transmitter circuit further includes a first mixer that combines the first frequency with a first input signal. The transmitter circuit also includes a first feedback loop. The first feedback loop includes a second mixer that combines the second frequency with a transmit signal and a first filter and a first adder that combines an output of the first mixer with an output of the first filter. The transmitter circuit also includes a third local oscillator that generates a third frequency equal to the receive frequency. The transmitter circuit further includes a third mixer that combines the third frequency with an output of the first adder.