Closed-Loop Tx Calibration Using DTC Frequency Separation
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Solution Overview
Problem
Current closed-loop transmitter calibration methods face challenges with harmonic aliasing and phase noise due to the use of multiple PLLs, which increase area and power consumption, and struggle to effectively separate IQ imbalance from transmitter impairments.
Innovation Solution
A closed-loop transmitter calibration system that generates both the Tx LO signal and LPBK LO signal from a single PLL source using a digital-to-time converter (DTC) circuit, downconverting the Tx output signal to an LPBK baseband signal at a frequency different from zero, thereby avoiding harmonic aliasing and reducing phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple PLLs are used for closed-loop transmitter calibration, then calibration functionality is provided, but area consumption and power consumption increase
Solution Approach 1:
The patent merges the functionality of multiple PLLs into a single PLL by using one PLL to generate both the Tx LO signal and the LPBK LO signal. This consolidation eliminates redundant circuitry, thereby reducing area consumption while maintaining the necessary calibration functionality through the unified phase-locked loop architecture.
Solution Approach 2:
The single PLL is designed to perform multiple functions: generating the Tx LO signal for the transmitter and generating the LPBK LO signal for the loopback receiver. This multi-functional approach allows one circuit to replace what previously required separate dedicated circuits, reducing overall area and power consumption.
2Reliability
If multiple PLLs are used for closed-loop transmitter calibration, then calibration functionality is provided, but power consumption increases
Solution Approach 1:
The patent merges the functionality of multiple PLLs into a single PLL by using one PLL to generate both the Tx LO signal and the LPBK LO signal. This consolidation eliminates redundant circuitry, thereby reducing area consumption while maintaining the necessary calibration functionality through the unified phase-locked loop architecture.
Solution Approach 2:
The single PLL is designed to perform multiple functions: generating the Tx LO signal for the transmitter and generating the LPBK LO signal for the loopback receiver. This multi-functional approach allows one circuit to replace what previously required separate dedicated circuits, reducing overall area and power consumption.
3Device complexity
If downconversion is performed at zero frequency, then calibration is simplified, but harmonic aliasing occurs
Solution Approach 1:
The patent changes the downconversion frequency parameter from zero frequency to a non-zero intermediate frequency. This parameter change shifts the downconverted signal away from DC, preventing harmonic aliasing while maintaining calibration functionality through the modified frequency domain operation.
4Reliability
If multiple PLLs are used for closed-loop transmitter calibration, then separate LO signals are generated, but phase noise correlation for cancellation is lost
Solution Approach 1:
The patent merges the functionality of multiple PLLs into a single PLL by using one PLL to generate both the Tx LO signal and the LPBK LO signal. This consolidation eliminates redundant circuitry, thereby reducing area consumption while maintaining the necessary calibration functionality through the unified phase-locked loop architecture.
Data Source
AI summary
A closed loop transmitter (Tx) calibration system is disclosed. The closed loop Tx calibration system comprises a transmitter circuit configured to generate a Tx output signal at a Tx output frequency based on a Tx local oscillator (LO) signal. The closed loop Tx calibration system further comprises a loop back (LPBK) receiver circuit coupled to the transmitter circuit and configured to downconvert the Tx output signal at the Tx output frequency to form an LPBK baseband signal at an LPBK intermediate frequency (IF), based on an LPBK LO signal. In some embodiments, the LPBK IF frequency is different from zero. In some embodiments, the closed loop Tx calibration system further comprises an LO generation circuit configured to generate the Tx LO signal and the LPBK LO signal from a single phase locked loop (PLL) source, based on utilizing a digital to time converter (DTC) circuit.