Electronic Filter Frequency Response Calibration
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Solution Overview
Problem
Current methods for calibrating electronic filters are inaccurate and require additional hardware, especially when trying to increase bandwidth without increasing undesired emissions, as they fail to account for active circuits and are inefficient for higher order filters.
Innovation Solution
A system using in-phase and quadrature baseband paths with numerically controlled oscillators, digital signal paths, and analog filters, where low and high frequency tones are applied to calibrate the corner frequency and peaking of the filter, with a peak detector determining amplitude differences to achieve equal outputs, allowing for precise calibration during standard transmission without additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the corner frequency of the baseband filter is increased to increase transmitter bandwidth, then the bandwidth is improved, but undesired emissions increase
Solution Approach 1:
The patent applies parameter changes by using digital equalization to modify the frequency response characteristics of the filter. Instead of changing the physical corner frequency of the analog filter, the system changes the effective frequency response through digital filtering and equalization, allowing bandwidth expansion without the corresponding increase in undesired emissions that would result from simply increasing the analog filter's corner frequency.
Solution Approach 2:
The patent introduces digital equalization as an intermediary between the analog filter and the output stage. This digital equalization component mediates the frequency response by compensating for filter droop and shaping the overall response, allowing the system to achieve desired bandwidth while maintaining control over undesired emissions through the digital domain rather than relying solely on analog filter characteristics.
2Speed
If digital equalization is used to correct filter droop and increase bandwidth, then bandwidth is improved, but calibration accuracy requirements increase
Solution Approach 1:
The patent implements feedback through an iterative calibration process where the system measures the actual frequency response of the filter and uses this information to adjust the digital equalization parameters. The calibration routine stimulates the filter with test signals, measures the output, compares it to the desired response, and adjusts the equalization coefficients accordingly, creating a closed-loop system that automatically achieves accurate calibration without requiring manual precision.
Solution Approach 2:
The system performs self-calibration by automatically measuring its own frequency response and adjusting its digital equalization parameters without external intervention. The calibration routine is executed within the transmitter itself, using built-in test signal generation and measurement capabilities, allowing the system to self-correct any deviations in filter response and maintain accurate operation.
3Measurement precision
If existing calibration methods are used, then calibration can be performed, but additional hardware or filter reconfiguration is required
Solution Approach 1:
The patent applies universality by using the existing operational amplifier circuits in the filter for multiple purposes - both for normal signal filtering and for calibration measurements. The same op-amps that perform the filtering function are also used to generate test signals and measure frequency response during calibration, eliminating the need for separate dedicated calibration hardware and allowing the existing circuitry to serve dual functions.
Solution Approach 2:
The filter calibration is performed using the filter's own internal circuits without requiring external test equipment or additional hardware components. The calibration routine uses the existing op-amps, capacitors, and resistors within the filter to generate test signals, measure responses, and adjust parameters, making the calibration process self-contained and eliminating the need for separate calibration hardware.
Data Source
AI summary
A system and method provide for calibrating the frequency response of an electronic filter. The system and method include a radio transmitter with both in-phase and quadrature baseband paths. Each baseband path includes a numerically controlled oscillator (“NCO”), a digital signal path, a digital-to-analog converter (“DAC”), and an analog filter. A low frequency tone is applied from the NCO from one of the baseband path, while a high frequency tone is applied from the NCO in the other baseband path. An analog peak detector at output determines which analog filter has the largest amplitude at the output. The peak detector offset between the two analog filters is offset by stimulating the in-phase and quadrature baseband paths with the respective NCOs to find an amplitude difference between the output signals from the NCOs that makes the output of the analog filters the same. Calibration is then performed on the corner frequency and filter peaking through respective stimulation of the in-phase and quadrature baseband paths. The system and method is advantageous as it allows for very accurate calibration of both the filter corner frequency and peaking during a standard transmission operating mode with little additional hardware required.