On-Chip Linearity Calibration Using Transmitter Signal Path
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Solution Overview
Problem
Direct-conversion receivers face significant distortion due to second-order intermodulation products from strong interfering signals in low supply environments, requiring highly linear receivers and external filters, which can disrupt normal operation and are sensitive to operating conditions, necessitating automatic background calibration.
Innovation Solution
Generating a two-tone calibration signal on-chip using the transmit signal path and injecting it into the receive signal path for linearity calibration during online or idle mode, allowing for calibration of the second-order input intercept point and residual sideband correction without affecting the receive signal path performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external filters are used to reduce distortion from strong interfering signals, then linearity is improved, but device complexity and sensitivity to operating conditions increase
Solution Approach 1:
The patent extracts the calibration function from external devices and implements it internally using on-chip test signal generation and injection circuitry. The test signal generator and injection mechanism are integrated within the receiver chip, removing the need for external filters and calibration equipment while maintaining linearity correction capabilities
Solution Approach 2:
The transmitter signal path is made multi-functional by enabling it to generate both normal transmit signals and calibration test signals. The same signal path hardware is used for dual purposes: regular communication transmission and linearity calibration, eliminating dedicated calibration hardware and reducing overall device complexity
2Reliability
If foreground calibration is performed to calibrate the receiver, then linearity is improved, but service interruptions occur
Solution Approach 1:
The patent implements periodic background calibration that can occur during idle periods or between data transmissions. The calibration process is scheduled to execute during natural gaps in communication activity, ensuring linearity maintenance without causing service interruptions. The system periodically injects test signals and adjusts coefficients automatically in the background
Solution Approach 2:
The receiver performs self-calibration using its own internal resources - the transmitter signal path generates test signals, the receiver signal path measures them, and the system automatically adjusts calibration coefficients without external intervention. This self-service capability enables background calibration that maintains linearity while keeping the device operational
3Device complexity
If the transmit signal path is used to generate calibration signals, then device complexity is reduced, but signal isolation becomes challenging
Solution Approach 1:
The patent introduces isolation switches as intermediary components that mediate between the transmitter signal path and receiver signal path during calibration. These switches act as controllable connectors that can be opened or closed to prevent unwanted signal leakage and interference, enabling safe use of the transmitter for generating calibration signals without compromising receiver performance
Data Source
AI summary
An apparatus including: at least one receiver having injection points and having at least an amplifier and a transformer; and a plurality of isolation switches coupled to injection points of the at least one receiver, the plurality of isolation switches configured to route a calibration signal generated by a transmitter to one of the injection points.