DC Detection Circuit for PCM Audio Signal Protection

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Solution Overview

Problem

In on-vehicle audio systems, the presence of direct current (DC) data in PCM data can cause loudspeakers to overheat and degrade or break due to constant currents flowing through them.

Innovation Solution

A DC detection circuit comprising an OR circuit, a NAND circuit, and a counter that generates flags to detect DC data in PCM input, triggering an error control circuit for overcurrent and overtemperature protection to prevent damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If DC data is included in PCM data input to audio systems, then the audio system can process the data, but loudspeakers will produce heat and cause breakage or degradation

Engineering Contradiction:

Improveaudio system data processing capabilityVSAvoidloudspeaker heat and degradation

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by detecting DC components in PCM data before the audio signal reaches the loudspeaker. The detection circuit analyzes the digital audio signal in advance, identifies DC offsets, and prevents them from causing harmful effects. This proactive approach allows the system to maintain full data processing capability while eliminating the harmful DC component before it can damage the loudspeaker.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If safety functions are improved in on-vehicle instruments, then reliability increases, but device complexity increases

Engineering Contradiction:

Improvesafety functionVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex analog DC detection methods with a digital signal processing approach. By using digital correlation computation between the input signal and a reference DC signal, the system achieves reliable DC detection without requiring complex analog circuitry. This substitution of digital processing for analog mechanisms maintains high reliability while reducing overall device complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses a reference signal that copies the characteristics of the DC component to be detected. By correlating the input signal with this reference copy, the system can accurately detect DC offsets through simple computational operations rather than complex filtering circuits. This copying approach simplifies the detection mechanism while maintaining detection accuracy.

Inventive Principle:

Principle #26Copying

Data Source

PatentUS10110996B2DC detection circuit and operational method of the same, semiconductor apparatus, and audio signal output apparatus

Publication Date: 2018.10.23 ROHM CO LTD

AI summary

The DC detection circuit includes: a OR circuit configured to generate a logical OR flag on the basis of logical OR of values of X bits from a (MSB-1)th bit to a (MSB-X)th bit of input data; a NAND circuit configured to generate a NAND flag on the basis of a NAND of values of X bits from the (MSB-1)th bit to the (MSB-X)th bit of the input data; a counter configured to count up and a counter value which outputs a DC detection flag if a counter value is exceeds predetermined set value on the basis of the MSB and any one of the logical OR flags of NAND flags. Accordingly, safety can be secured by detecting whether the DC data is included in the input PCM data, and thereby preventing degradation and breakage of the loudspeaker etc. due to the DC data.