Differential Active RC Filter Calibration Without Reference Buffers
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Solution Overview
Problem
Existing active RC filter calibration methods require additional RC arrays, reference voltage circuits, and voltage buffers, leading to increased circuit complexity and area usage, while conventional methods do not effectively address deviations due to PVT changes.
Innovation Solution
A calibration method for on-chip differential active RC filters that multiplexes the capacitor array, eliminates the need for a reference voltage and voltage buffer, and uses a fully differential circuit structure with pulse generation and zero-crossing detection to achieve accurate calibration through successive approximation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional RC arrays are used for calibration testing, then calibration accuracy is improved, but chip area increases
Solution Approach 1:
The filter's own RC arrays are made to serve dual purposes: both signal filtering and calibration testing. The control unit configures the RC arrays to operate in calibration mode, eliminating the need for separate dedicated test RC arrays and reducing chip area while maintaining calibration accuracy.
Solution Approach 2:
The filter performs self-calibration by using its own internal RC arrays and operational amplifiers for testing. The calibration circuit leverages the filter's existing components to measure and adjust its own time constants, eliminating dependency on external reference circuits and reducing overall circuit complexity.
2Ease of operation
If reference voltage circuits and voltage buffers are added for calibration, then calibration functionality is improved, but circuit complexity increases
Solution Approach 1:
The filter uses its own operational amplifiers and RC configurations to generate and reference voltages during calibration. The fully differential structure allows direct comparison of differential voltages without requiring external reference voltage circuits or buffer amplifiers, simplifying the overall circuit architecture.
Solution Approach 2:
The calibration method extracts and eliminates unnecessary external reference circuits and voltage buffers from the traditional calibration architecture. By using the filter's internal fully differential structure for direct voltage comparison, the design removes redundant components while preserving calibration functionality.
3Ease of manufacture
If conventional calibration methods are used, then calibration process is simple, but PVT deviation compensation is insufficient
Solution Approach 1:
The calibration method implements a feedback mechanism where the control unit continuously monitors the filter's time constant through the fully differential structure and adjusts the RC configurations accordingly. This closed-loop approach compensates for PVT variations by dynamically adapting the filter parameters to maintain accurate bandwidth despite process, voltage, and temperature changes.
Solution Approach 2:
The RC arrays are designed with dynamic reconfigurability, allowing the resistance and capacitance values to be adjusted in real-time based on operating conditions. The control unit dynamically selects different RC configurations to compensate for PVT deviations, transforming the static filter into an adaptive system that maintains performance across varying environmental conditions.
Data Source
AI summary
A calibration method and a tuning method for an on-chip differential active RC filter are provided. The calibration method comprises: obtaining zero-crossing time of a differential signal outputted by a single-pole point real number filter by analyzing the single-pole point real number filter; setting a reference clock period according to the relationship between the zero-crossing time and the bandwidth of the single-pole point real number filter, and setting a calibration working time sequence according to the reference clock period; and scanning an RC configuration of an RC array according to the calibration working time sequence to realize calibration of the RC array.