Integrated RF Filter with Calibration for Selectivity and Linearity
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Solution Overview
Problem
Current DVB-S broadband tuners face challenges in detecting weak RF signals amidst strong unwanted signals due to multiple channels and out-of-band interference, requiring high selectivity and linearity, which is difficult to achieve with existing filtering methods that degrade noise figure and impedance.
Innovation Solution
An integrated RF filter circuit with an adjustable capacitive array and a calibration system that uses a local oscillator to generate calibration signals, allowing for precise tuning and calibration of the filter settings to enhance selectivity and linearity, while maintaining low noise and constant impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If filtering is performed at RF frequency, then selectivity is improved, but linearity constraints become problematic when multiple carriers with strong levels are present
Solution Approach 1:
The patent implements a dynamically adjustable RF filter with electronically controllable tuning elements that can adapt their characteristics based on operating conditions. This allows the filter to maintain optimal selectivity while accommodating varying signal levels and preventing saturation, thereby resolving the contradiction between selectivity and linearity under multiple strong carrier conditions.
Solution Approach 2:
The patent employs variable filter parameters including adjustable center frequency, bandwidth, and Q-factor through electronic control mechanisms. By dynamically changing these parameters based on the presence and strength of multiple carriers, the system maintains high selectivity for desired signals while preventing overload and distortion from strong unwanted signals, thus resolving the linearity constraint problem.
2Measurement precision
If filtering is performed at low frequency, then most filtering is achieved, but RF stages and mixers have linearity constraints that become problematic
Solution Approach 1:
The patent applies preliminary filtering action at the RF stage before the signal reaches the mixer and subsequent low-frequency processing stages. By performing initial rejection of strong unwanted RF signals at the front end, the system prevents these signals from causing saturation and intermodulation distortion in later stages, thereby maintaining linearity while still achieving effective filtering.
Solution Approach 2:
The patent implements a dynamically adjustable RF filter with electronically controllable tuning elements that can adapt their characteristics based on operating conditions. This allows the filter to maintain optimal selectivity while accommodating varying signal levels and preventing saturation, thereby resolving the contradiction between selectivity and linearity under multiple strong carrier conditions.
3Measurement precision
If external passive components are used for filtering, then unwanted signals are filtered, but space is taken, noise figure is degraded and input impedance is not constant over frequency
Solution Approach 1:
The patent integrates the RF filter functionality directly into the receiver circuitry, merging previously separate external passive filtering components with the active RF front-end circuit. This integration eliminates the need for discrete external filters, reduces overall device complexity, maintains constant input impedance across frequency, and prevents noise figure degradation while still achieving effective signal filtering.
Solution Approach 2:
The patent employs an active integrated filter circuit that serves as an intermediary between the antenna input and subsequent RF stages. This active filter provides the necessary frequency selection and rejection of unwanted signals while maintaining proper impedance matching and noise performance, replacing the need for external passive components.
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
The solution provides improved front-end selectivity and sensitivity in the presence of strong unwanted signals, ensuring reliable signal detection and reducing errors in filter components, thereby enhancing the overall performance of the RF receiver.
Implementation Method 1
A local oscillator (LO) generates a LO signal and an RX_LO signal from the LO signal. A mixing circuit mixes a signal received from the adjustable RF filter circuit and the RX_LO signal.
Implementation Method 2
A calibration circuit implements a calibration mode and a receive mode. In the calibration mode, the calibration circuit generates a calibration signal from the LO signal, injects the calibration signal into the receive path of the RF receiver circuit and before the adjustable RF filter, enables the use of the IF_cal signal in calibrating the receiver circuit; and responsive to the injected calibration signal and an output of the mixing circuit, assesses a setting of the adjustable RF filter circuit using a feedback signal.
Data Source
AI summary
Radio-frequency (RF) circuits, methods and systems are implemented according to a variety of embodiments. According to one such embodiment, a radio-frequency (RF) receiver circuit is implemented with an adjustable RF filter circuit in a receive path of the RF receiver circuit. A local oscillator (LO) generates a LO signal and an RX_LO signal from the LO signal. A mixing circuit mixes a signal received from the adjustable RF filter circuit and the RX_LO signal. An intermediate-frequency (IF) circuit generates an IF_cal signal at the receiver circuit. A calibration circuit implements both a calibration mode and a receive mode. In the calibration mode, a calibration signal is injected into the receive path. A setting of the adjustable RF filter circuit is determined. In the receive mode, the calibration circuit disables the injection of the calibration signal into the receive path of the RF receiver circuit.