FSK Transceiver Filter Calibration Using PLL Phase Detection
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Solution Overview
Problem
Existing transceivers face challenges in calibrating receiver and transmitter filters, particularly in maintaining the center frequency of band-pass filters due to process variations, which requires additional circuitry and increases complexity and risk.
Innovation Solution
A method that uses existing circuitry in a frequency shift keying (FSK) transceiver to calibrate the center frequency of band-pass filters by employing a phase-frequency detector, charge pump, and voltage controlled oscillator within a phase locked loop, and also calibrates the squelch detector threshold, eliminating the need for extra circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If filter calibration is performed using traditional methods, then manufacturing precision is improved, but device complexity increases due to extra circuitry
Solution Approach 1:
The existing PLL circuitry is made multi-functional by using it for both normal frequency synthesis operations and filter calibration operations. The charge pump and PFD are reused for calibration without requiring separate dedicated calibration circuits, thereby improving manufacturing precision while avoiding increased device complexity.
Solution Approach 2:
The system performs self-calibration using its own internal resources. The PLL circuitry calibrates the filter by adjusting its own parameters through the charge pump based on feedback from the PFD, eliminating the need for external calibration equipment or additional calibration-specific circuitry.
2Manufacturing precision
If additional circuitry is added for filter calibration, then manufacturing precision is improved, but die area increases
Solution Approach 1:
The same circuit blocks (PFD, charge pump, PLL) are used for both normal operation and calibration functions. This multi-functionality allows the system to achieve precise filter calibration without adding any extra die area, as no new physical circuits are introduced.
Solution Approach 2:
The calibration function is merged with the existing PLL frequency synthesis function. By combining these functions into a single integrated system rather than separate circuits, the patent achieves calibration capability without increasing die area.
3Manufacturing precision
If traditional filter calibration methods are used, then filter performance is improved, but reliability decreases due to higher risk from additional circuitry
Solution Approach 1:
By making the PLL circuitry multi-functional for both synthesis and calibration, the patent eliminates additional calibration-specific circuits that would introduce new failure modes. The same proven circuit blocks are used for both functions, maintaining reliability while achieving calibration accuracy.
Solution Approach 2:
The self-calibrating system reduces reliability risks by eliminating external calibration interfaces and additional calibration circuits. The system uses its own internal feedback mechanisms to maintain accuracy, reducing points of failure associated with external calibration equipment or additional calibration path circuitry.
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
This approach allows for low-risk, low-complexity filter calibration without additional die area, absorbing gain variations and component mismatches in the squelch detection threshold level, ensuring accurate filter performance and system stability.
Implementation Method 1
detecting, by a phase-frequency detector ('PFD'), a difference in phase between the carrier frequency signal and the filtered signal from the BPF
Implementation Method 2
selecting, by the multiplexer, to receive a signal from a voltage controlled oscillator ('VCO') in a phase locked loop ('PLL') during a normal operation of the FSK transceiver
Data Source
AI summary
Various embodiments relate to a method for calibration of a center frequency of a BPF in an FSK transceiver, the method including the steps of filtering a carrier frequency signal by the BPF to produce a filtered signal, detecting, by a phase-frequency detector (“PFD”), a difference in phase between the carrier frequency signal and the filtered signal from the BPF, sweeping a calibration code of the BPF, detecting a transition in the sign of the phase difference and capturing a calibration code associated with the transition in the sign of the phase difference for calibration of the BPF.