Signal Path DC Offset Calibration Without Output Transient Noise
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Solution Overview
Problem
Signal processing apparatuses face challenges in calibrating DC levels without introducing transient noise, as existing methods either measure DC levels post-power application, causing noise, or fail to account for subsequent stage offsets, leading to residual DC offsets and inefficiencies.
Innovation Solution
A signal processing apparatus with a switch mechanism and auxiliary stage that allows for DC level calibration by generating a control signal indicative of the DC offset at the output of the second signal processing stage, enabling adjustment of the DC level before the output, using feedback for linear amplification and non-linear amplification in the auxiliary stage for accurate calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC level is measured at the output of the signal processing apparatus, then the DC offset can be accurately measured, but transient noise is generated and passed to other coupled equipment
Solution Approach 1:
The patent applies preliminary action by measuring the DC level at an intermediate stage (output of first signal processing stage) before the signal proceeds to the second stage, rather than at the final output. This allows DC calibration to be performed in advance without exposing connected equipment to transient noise that would occur if measurement and calibration were done at the final output stage after power application.
2Object-affected harmful factors
If DC level is measured at an earlier stage of the signal path, then transient noise is avoided, but any DC offset in subsequent stages is not taken into account, resulting in residual DC offset at the output
Solution Approach 1:
The patent implements feedback by using the output of the second signal processing stage (which contains the DC offset from that stage) to generate a control signal that is fed back to adjust the DC level at the first stage. This feedback mechanism ensures that the calibration process accounts for DC offsets in subsequent stages, eliminating residual DC offset at the final output while still measuring at the intermediate stage to avoid transient noise.
3Measurement precision
If a measurement device with very low DC offset is used, then measurement inaccuracy is avoided, but the device occupies large silicon area and reduces power efficiency
Solution Approach 1:
The patent applies self-service by using the second signal processing stage itself to generate the control signal for calibration, rather than requiring a separate low-DC-offset measurement device. The second stage's output is used to create the control signal that adjusts the first stage's DC level, allowing the system to perform its own calibration function using existing components, thereby avoiding the need for additional power-hungry measurement hardware.
4Ease of operation
If DC calibration is performed with power applied, then the DC level can be adjusted, but transient noise is generated during calibration
Solution Approach 1:
The patent applies segmentation by dividing the signal processing path into distinct stages (first and second stages) with an intermediate measurement point. This segmentation allows DC calibration to be performed at the intermediate stage rather than at the final output, enabling calibration functionality while isolating connected equipment from transient noise generation during the calibration process.
Data Source
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AI summary
A signal processing apparatus (200, 300) comprises a signal path including first and second signal processing stages (210, 220) for processing a signal. There is a switch means (260, 410a, 410b, 420a, 420b) for, in a first state, coupling an output of the first signal processing stage (210) to an input (222) of the second signal processing stage (220), and, in a second state, de-coupling the output of the first signal processing stage (210) from the input (222) of the second signal processing stage (220). There is an auxiliary stage (230) coupled to the output of the first signal processing stage (210) and arranged to generate a control signal dependent on a DC level at the output of the first signal processing stage (210) and on a DC level in the auxiliary stage (230) and indicative of a DC offset at an output (224) of the second signal processing stage (220). There is a calibration means (240) for, responsive to the control signal, adjusting a DC level in the signal path at a location preceding the output of the first signal processing stage (210) when the switch means (260, 410a, 410b, 420a, 420b) is in the second state.