Variable gain amplification device and two-input amplification device

A two-input amplification device comprising:

• a splitter to split an amplification target signal into two signals, and output one signal and an other signal which are included in the two signals;
• a first variable gain amplifier to amplify the one signal in accordance with first variable gain characteristics, the first variable gain amplifier having the first variable gain characteristics whose gain corresponding to a control signal indicating a magnitude of an envelope of the amplification target signal is expressed by a first sigmoid function;
• a second variable gain amplifier to amplify the other signal in accordance with second variable gain characteristics, the second variable gain amplifier having the second variable gain characteristics whose gain corresponding to the control signal is expressed by a second sigmoid function;
• a characteristics adjuster to adjust one or more gains among a gain of the first sigmoid function and a gain of the second sigmoid function depending on a frequency of the amplification target signal;
• and
• a two-input amplifier to output a synthesis signal of one signal amplified by a first amplification element and an other signal amplified by a second amplification element, the two-input amplifier including the first amplification element to amplify the one signal amplified by the first variable gain amplifier, and the second amplification element to amplify the other signal amplified by the second variable gain amplifier.