agc & alc
AGC typically applies to receivers. In any band of frequencies, there exists the channel you want to receive plus interferers. To guarantee certain SNDR at the ADC output, you need to have a particular input signal amplitude to the ADC. If your channel is weaker that that level, you need to re-adject the gains in the receiver chain to get your channel level right and vice versa.
ALC refers to level adjustment loops. This can be applied to any circuit not an entire system or sub-system. A prime example is ALC loops used to regulate oscillator's amplitude to suppress amplitude noise or reduce current 0ver-design factors.
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