Active Biquad Filter Calibration Using Oscillation and Negative Gm
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Solution Overview
Problem
Tunable active filters in wireless communication networks face challenges in maintaining high quality factor (Q) and center frequency stability due to process variations, mismatch, and operational amplifier limitations, requiring effective calibration methods.
Innovation Solution
A tunable active filter configuration using a negative transconductance circuit and resistor-capacitor (RC) topology, which includes a method for determining error values and generating calibration parameters to adjust impedance, allowing the filter to oscillate and calibrate center frequencies without sweeping the entire bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional sweeping methods are used to calibrate the entire bandwidth, then comprehensive frequency coverage is achieved, but calibration time and complexity increase significantly
Solution Approach 1:
The patent divides the bandwidth calibration process into multiple frequency segments. Instead of sweeping the entire bandwidth continuously, the calibration is performed in discrete frequency segments using the oscillation mode at specific points, significantly reducing calibration time while maintaining accuracy across the full bandwidth range.
Solution Approach 2:
The patent performs preliminary calibration by determining error values at specific frequency points using oscillation mode before full bandwidth operation. These preliminary error measurements are then used to generate calibration parameters that compensate for frequency-dependent errors across the entire bandwidth, avoiding the need for time-consuming continuous sweeping.
2Reliability
If high quality factor (Q) and high center frequency (f0) are targeted, then filter performance is improved, but Q and f0 vary due to process variations and operational amplifier limitations
Solution Approach 1:
The patent implements a feedback mechanism where error values are measured at specific frequency points using oscillation mode, and calibration parameters are generated based on these measurements. These calibration parameters are then applied to compensate for process variations and operational amplifier limitations, stabilizing Q and f0 across different manufacturing conditions.
Solution Approach 2:
The patent changes the impedance parameter of the negative transconductance circuit based on measured error values. By adjusting the impedance according to frequency-dependent error characteristics, the system compensates for manufacturing variations and maintains consistent filter performance across different production batches and operating conditions.
3Measurement precision
If full bandwidth sweeping is performed for calibration, then complete frequency coverage is achieved, but hardware costs and power consumption increase
Solution Approach 1:
The patent segments the calibration process to operate only at specific frequency points using oscillation mode rather than continuously sweeping the entire bandwidth. This segmented approach maintains frequency response accuracy while significantly reducing power consumption by activating the oscillation circuit only when needed for error measurement at discrete frequencies.
Solution Approach 2:
The patent uses periodic oscillation mode at specific frequency points for calibration rather than continuous sweeping. The oscillation circuit is activated periodically at predetermined frequencies to measure error values, then deactivated during normal filter operation, reducing overall power consumption while maintaining calibration accuracy.
Data Source
AI summary
Certain aspects of the present disclosure are generally directed to a tunable active filter and a method of calibrating a tunable active filter. One example apparatus is a filter circuit that generally includes a resistor-capacitor (RC) topology tunable active filter comprising a first amplifier, a second amplifier, and a feedback path coupled between an input of the first amplifier and an output of the second amplifier. The filter circuit also includes a negative transconductance circuit coupled to a first node of the tunable active filter.