I/Q DC Offset and Imbalance Compensation for NBI Filter Performance
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Solution Overview
Problem
Communications devices, such as handheld radios, face performance degradation due to in-phase (I) and quadrature (Q) DC offsets and gain and phase imbalances, which compromise the narrowband interferer (NBI) excision filter's effectiveness, especially when processing signals with multiple narrowband signals.
Innovation Solution
A communications device with an integrated receiver design that includes an analog-to-digital converter, DC offset estimator and removal circuit, gain imbalance estimator and compensator circuit, and phase imbalance estimator and compensator circuit, which sample and compensate I and Q signal components to eliminate DC offsets and imbalances, allowing the NBI filter to process only the primary signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a low cost in-phase/quadrature demodulator is used, then device cost is reduced, but DC offsets and gain/phase imbalances degrade signal quality and NBI filter performance
Solution Approach 1:
The patent applies preliminary action by performing DC offset estimation and removal, as well as gain and phase imbalance compensation, before the NBI excision filter processes the signal. The DC offset removal circuit estimates and subtracts DC offsets from I and Q channels, and the gain/phase imbalance compensator adjusts amplitude and phase differences ahead of time, preparing a cleaner signal for subsequent filtering operations.
Solution Approach 2:
The patent introduces intermediary compensation circuits between the low-cost demodulator and the NBI filter. The DC offset removal circuit and gain/phase imbalance compensator act as mediators that condition the signal, eliminating harmful DC components and imbalances, thereby enabling the NBI filter to operate effectively despite the use of inexpensive demodulator components.
2Reliability
If multiple narrowband signals are present in the received signal, then the NBI excision filter performance is degraded, but using high quality RF parts to minimize degradation increases device cost
Solution Approach 1:
The patent extracts and removes DC offset components and conjugate image signals caused by gain and phase imbalances before the NBI excision filter processes the signal. By taking out these harmful intermediate frequency components through DC offset removal and imbalance compensation, the NBI filter only needs to handle the actual narrowband interferers, significantly improving its performance without requiring expensive high-quality RF parts.
3Productivity
If DC offsets and gain/phase imbalances are not compensated, then the NBI filter must process multiple signals including spurs, but compensation circuits are needed to clean the signal spectrum
Solution Approach 1:
The patent performs preliminary signal conditioning by estimating and removing DC offsets and compensating for gain and phase imbalances before the NBI excision filter operates. This preliminary action reduces the number of signals the filter must process, improving productivity. The compensation circuits, while adding some complexity, use standard signal processing techniques that are computationally efficient and can be implemented in software-defined radio architectures.
Data Source
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AI summary
A DC offset estimator and removal circuit removes the DC offsets for each of the I and Q signal components in a received signal. A gain imbalance estimator and compensator circuit estimates and compensates for gain imbalances within the I and Q signal components. A phase imbalance estimator and compensator circuit estimates and compensates for phase imbalances within the I and Q signal components to produce a communications signal that is compensated for received DC offsets and gain and phase imbalances within the I and Q signal components.