Modulation is the act of translating some low-frequency or baseband signal (voice, music, and data) to a higher frequency. Why do we modulate signals? There are at least two reasons: to allow the ...

Lock-in amplifiers were invented in the 1930s [1, 2, 3] and commercialized [4] in the mid 20 th century as electrical instruments that are capable of extracting signal amplitudes and phases in ...