Direct Conversion Receiver Baseband Processing for Noise and Bandwidth Trade-offs
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Solution Overview
Problem
Direct conversion radio receivers face challenges in achieving good low frequency noise performance and high amplifier bandwidth simultaneously while maintaining low dissipated power, as large transistors required for low frequency noise reduction introduce parasitic capacitances that reduce bandwidth, and increasing power consumption is contraindicated in wireless and mobile applications.
Innovation Solution
The method involves diplexing the analog baseband signal into two overlapping spectra and recombining them in the digital domain to relax flicker noise requirements, increase bandwidth, and reduce total dissipated power, while independently optimizing low and high frequency paths for noise performance and using aliasing correlation to reduce aliasing effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the size of transistor devices in an amplifier is increased to reduce flicker noise, then low frequency noise performance is improved, but amplifier bandwidth is reduced due to large parasitic capacitances
Solution Approach 1:
The baseband signal is divided into two separate frequency paths: a low frequency path (0-10 MHz) processed by a first amplifier optimized for low frequency noise performance, and a high frequency path (10 MHz-20 MHz) processed by a second amplifier optimized for bandwidth. This segmentation allows each amplifier to be independently optimized for its specific frequency range, resolving the contradiction between low frequency noise performance and bandwidth.
2Speed
If the dissipated power of the amplifier is increased to reduce bandwidth loss, then amplifier bandwidth is improved, but power consumption increases which is contraindicated in wireless and mobile applications
Solution Approach 1:
The signal processing is segmented into two parallel paths with separate amplifiers. The first amplifier handles low frequency content with optimized low frequency performance at lower power, while the second amplifier handles high frequency content with optimized bandwidth. This segmentation achieves high overall bandwidth without requiring either amplifier to consume excessive power, as each is sized appropriately for its specific frequency range rather than requiring one large high-power amplifier to cover the entire bandwidth.
3Device complexity
If a single amplifier is used to cover the entire baseband frequency range, then device complexity is reduced, but it cannot simultaneously achieve good low frequency noise performance and high bandwidth
Solution Approach 1:
The baseband processing is segmented into two independent frequency paths, each with its own optimized amplifier. The first amplifier is designed specifically for low frequency optimization with appropriate compensation, while the second amplifier is designed for high frequency optimization. This segmentation resolves the contradiction by allowing each amplifier to be independently optimized for its specific frequency range, achieving both good low frequency noise performance and high overall bandwidth that a single amplifier cannot provide.
Solution Approach 2:
Each amplifier is designed with local quality optimized for its specific frequency range. The first amplifier has compensation tailored for low frequency response, while the second amplifier has compensation optimized for high frequency response. This local optimization allows each component to perform at its best for its designated frequency range, achieving superior overall system performance compared to a single general-purpose amplifier.
Data Source
AI summary
A method and apparatus are provided for reducing aliasing in a direct conversion (or zero-IF) radio receiver having high and low frequency paths. According to an implementation, a non-transitory machine-readable memory stores aliasing correlation response data that associates a measured non-aliased signal in a high frequency path and a measured aliased residual of the signal in a low frequency path. A compensator is in communication with the memory to apply aliasing compensation to received signals based on the stored aliasing correlation response data. In an example implementation, the low and high frequency paths are independently optimized for low and high frequency performance, respectively, and have transfer functions that overlap with one another to create a calibration zone used to calibrate the first and second transfer functions.