Transceiver Transmit-Chain Calibration for RF Droop and Spurs
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Solution Overview
Problem
Superheterodyne transceivers face challenges in satisfying spectral emission mask requirements due to spurs introduced during up-conversion from intermediate frequency to radio frequency, which can lead to undesirable droop in the amplitude of the transmitted RF signal.
Innovation Solution
A calibration mode of operation is implemented using RF calibration signals generated through mixing and amplification, allowing for the adjustment of transmit chain impedance to mitigate spurs and droop, employing direct conversion mixing and heterodyne mixing techniques to reduce spurious emissions and optimize capacitance settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If tunable capacitors are added to the transmitter amplifier chain to reduce spurs, then spectral emission mask requirements are satisfied, but amplitude droop in the transmitted RF signal increases
Solution Approach 1:
The patent performs droop calibration during the manufacturing process to pre-determine the optimal capacitance values for each amplifier stage. By measuring and storing the actual droop characteristics of each device before it leaves the factory, the system can apply pre-calculated compensation values during normal operation, eliminating the need for runtime adjustments while maintaining both low spurs and accurate amplitude
Solution Approach 2:
The patent changes the capacitance values of tunable capacitors in the amplifier chain based on the calibrated droop characteristics. By adjusting these capacitance parameters according to pre-stored calibration data, the system compensates for amplitude droop while maintaining the spur-reducing effect of the additional capacitance
2Object-generated harmful factors
If additional capacitance is configured in the transmitter amplifier chain to satisfy spectral emission mask, then spurious emissions are reduced, but transmit signal power decreases
Solution Approach 1:
The system performs power calibration during manufacturing to pre-determine the optimal capacitance settings that balance spur reduction with power maintenance. By storing these pre-calculated compensation values, the system can maintain transmit power levels without requiring complex runtime power measurement and adjustment mechanisms
Solution Approach 2:
The patent implements a feedback mechanism where the measured output power and droop characteristics are used to adjust the capacitance values of tunable capacitors in subsequent amplifier stages. This feedback loop ensures that the total capacitance added across the chain reduces spurs while compensating for power loss through intelligent distribution of capacitance values
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
The solution effectively reduces spurious emissions, ensuring compliance with spectral emission mask requirements while maintaining RF signal amplitude, thereby enhancing the performance of superheterodyne transceivers.
Implementation Method 1
a signal multiplier configured to mix the local oscillator signal with a frequency-translated version of the local oscillator signal to form an RF calibration signal
Implementation Method 2
a second mixer configured to mix the RF calibration signal with a DC offset signal to form a mixed RF calibration signal
Implementation Method 3
amplifying the mixed RF calibration signal through a transmit chain in the transceiver to form an amplified mixed RF calibration signal
Data Source
AI summary
A transceiver is configured for a calibration mode of operation in which an impedance of a transmit chain is tuned responsive to a power measurement of a mixed RF calibration signal to form a tuned transmit chain. A direct conversion mixes an RF calibration signal with a DC offset signal to form the mixed calibration signal. During a normal mode of operation, a heterodyne mixer mixes an LO signal with an IF signal to produce an RF signal that is amplified through the tuned transmit chain.