Biquad Filter Oscillation Calibration for Center Frequency and Q
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Solution Overview
Problem
Tunable active filters in wireless communication networks face challenges in accurately calibrating center frequency and quality factor due to process variations and operational amplifier limitations, leading to suboptimal performance and increased hardware and power consumption.
Innovation Solution
A filter circuit with an amplitude-limiting circuit and a Tow-Thomas biquad filter configuration, which generates an oscillating signal to calibrate the center frequency and quality factor by adjusting programmable capacitors and resistors, using an amplitude limiter with NMOS and PMOS transistors and a biasing circuit to prevent signal saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods are used to calibrate center frequency and quality factor, then calibration accuracy may be maintained, but hardware complexity and power consumption increase due to bandwidth sweeping requirements
Solution Approach 1:
The patent changes the calibration approach from bandwidth sweeping to oscillation frequency measurement. By converting the filter to oscillation mode and measuring the oscillation frequency, the calibration process avoids complex bandwidth sweeping hardware while achieving accurate center frequency and quality factor calibration through parameter transformation
Solution Approach 2:
The patent replaces the mechanical bandwidth sweeping process with an electrical oscillation-based measurement system. Instead of using complex signal injection and bandwidth measurement circuits, the system uses the filter's own oscillation characteristics to determine calibration parameters, simplifying the hardware architecture
2Measurement precision
If traditional calibration methods are used to calibrate center frequency and quality factor, then calibration accuracy may be maintained, but power consumption increases due to continuous bandwidth sweeping
Solution Approach 1:
The patent uses periodic oscillation to perform calibration instead of continuous bandwidth sweeping. The filter is temporarily converted to oscillation mode, allowing calibration measurements to be taken during the oscillation cycles, then returned to filter mode. This periodic approach significantly reduces power consumption compared to continuous sweeping operations
Solution Approach 2:
The patent enables the filter to calibrate itself using its own oscillation characteristics. The oscillation frequency and amplitude naturally provide the information needed for calibration, eliminating the need for external calibration signals and reducing overall power consumption by using the system's inherent properties for self-diagnosis and adjustment
3Illumination intensity
If amplitude is not limited during oscillation calibration, then oscillation signal strength may be increased, but signal saturation occurs leading to calibration errors
Solution Approach 1:
The patent implements amplitude limiting through feedback control during oscillation calibration. The oscillation amplitude is monitored and controlled to remain within linear operating ranges, preventing saturation while maintaining sufficient signal strength for accurate frequency measurement. This feedback mechanism ensures reliable calibration by keeping the signal in the optimal range
Solution Approach 2:
The patent applies amplitude limiting beforehand during the oscillation calibration process to prevent signal saturation before it occurs. By controlling the oscillation amplitude from the start rather than correcting saturation effects afterward, the system avoids calibration errors and maintains accuracy throughout the measurement process
4Device complexity
If process variations and operational amplifier limitations are not compensated, then circuit simplicity is maintained, but center frequency and quality factor accuracy deteriorate
Solution Approach 1:
The patent enables the filter circuit to automatically compensate for process variations and operational amplifier limitations through self-calibration. By measuring the actual oscillation frequency and comparing it to the desired center frequency, the system automatically adjusts calibration parameters to correct for manufacturing variations and component limitations without adding complex compensation circuits
Data Source
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AI summary
Certain aspects of the present disclosure provide methods and apparatus for calibrating a tunable active filter. One example apparatus is a filter circuit that generally includes a tunable active filter comprising at least one amplifier and a first feedback path coupled between an input and an output of the at least one amplifier, the first feedback path comprising at least one switch; and an amplitude limiter coupled to the tunable active filter and comprising at least one transistor disposed in a second feedback path coupled between the input and the output of the at least one amplifier.