AN3673| Application Note
Maxim/Dallas > App Notes > AUDIO CIRCUITS Keywords: MAX9756, ALC, Automatic Level Control, AGC, Automatic Gain Control, Maxim
Oct 18, 2005
APPLICATION NOTE 3673
An Overview of Automatic Level Control
Automatic Level Control (ALC) is a technology that automatically controls output power to the speaker. ALC prevents loudspeaker overload and optimizes dynamic range. This application note presents ALC technology and demonstrates its use in the MAX9756/MAX9757/MAX9758 stereo speaker amplifiers. Maxim's Automatic Level Control (ALC) offers two key benefits (Figures 1 and 2). 1. It protects the loudspeaker by limiting the amplifier output power. 2. It boosts low-level signals without distorting the high-level signals. ALC is implemented in the MAX9756, MAX9757, and MAX9758 2.3W stereo speaker amplifiers and DirectDrive headphone amplifiers.
Figures 1 and 2. The MAX9756's automatic level control (ALC) function protects the speakers without adding distortion.
ALC vs. Output Limiting
ALC differs from traditional output limiting. An output-limiter function limits the output swing at a predetermined level so that the transducer is protected from overvoltage peaks. Clipping (distortion) is added at the output signal as a result (Figure 3). An ALC function, however, reduces the gain so that the transducer is protected. No distortion is added (Figure 4).
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