Signal Path DC Calibration Using an Auxiliary Offset Stage
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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 at the output, causing noise to other equipment, or fail to account for DC offsets in subsequent stages, leading to residual offsets and inefficiencies.
Innovation Solution
A signal processing apparatus with a switch mechanism and an auxiliary stage that generates a control signal based on DC levels, allowing for calibration of the DC level before the output stage, thereby adjusting the DC level in the signal path without affecting the second processing stage and reducing transient noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC level is measured at the output of the signal processing apparatus, then the measurement reflects the actual output DC offset, but transient noise is generated and passed to other coupled equipment
Solution Approach 1:
The signal path is segmented into multiple stages, and the DC calibration is performed at an intermediate stage rather than at the final output. This segmentation allows the measurement to be taken before the transient noise-generating power-on sequence completes, thus avoiding the harmful transient noise while still enabling accurate DC level measurement through the auxiliary stage that mirrors the second stage's characteristics
Solution Approach 2:
An auxiliary stage is introduced as an intermediary element that replicates the DC characteristics of the second signal processing stage. This auxiliary stage serves as a mediator that allows DC measurement and calibration without requiring the actual second stage to be active, thereby preventing transient noise generation while maintaining measurement accuracy
2Object-generated 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 auxiliary stage is designed as a copy or replica of the second signal processing stage, specifically mirroring its DC characteristics and offset behavior. This copying approach allows the calibration performed at the earlier stage to account for the DC offset that would otherwise be introduced by the second stage, thereby achieving accurate overall DC calibration without activating the second stage and generating transient noise
3Measurement precision
If a measurement device with very low DC offset is used to avoid measurement inaccuracy, then measurement precision is improved, but the device occupies large silicon area and reduces power efficiency
Solution Approach 1:
The auxiliary stage serves itself by using its own DC characteristics and internal signal path to perform the calibration measurement. Instead of requiring an external high-precision measurement device with large silicon area, the system uses its existing auxiliary stage infrastructure to generate and measure the DC level, thereby achieving accurate measurement without the need for additional complex measurement hardware
4Manufacturing precision
If a step in DC level is applied during calibration in audio signal processing apparatus, then the DC offset is adjusted, but audible noise is generated
Solution Approach 1:
The DC calibration is performed as a preliminary action during the power-on sequence, adjusting the DC offset in the first stage before the second stage is activated. By completing the DC adjustment beforehand and using the auxiliary stage to simulate the second stage's DC characteristics, the calibration can be performed without applying large DC steps to the final output, thereby preventing audible noise while still achieving precise DC offset calibration
Data Source
AI summary
A signal processing apparatus is provided that comprises a signal path including first and second signal processing stages for processing a signal. A switch, in a first state couples and in a second state de-couples an output of the first signal processing stage to an input of the second signal processing stage. An auxiliary stage coupled to the output of the first signal processing stage generates a control signal dependent to a DC level at the output of the first signal processing stage, on a DC level in the auxiliary stage, and indicates a DC offset at an output of the second signal processing stage. A calibration circuit, responsive to the control signal, adjusts a DC level in the signal path preceding the output of the first signal processing stage when the switch is in the second state.