Editing Product detector (section)

==A more sophisticated  product detector==
A more sophisticated product detector can be constructed in a way much like a single-sideband modulator.  Two copies of the modulated input signals are created.  The first copy is mixed with a local oscillator and [[low-pass filter]]ed.  The second copy is mixed with a 90° phase-shifted copy of the oscillator and  the output of this mixer is also 90° phase-shifted and then low-pass filtered.  These copies are then combined to produce the original message. This operation is similar to that performed by a dual-phase [[lock-in amplifier]].
Example: I-Q Demodulator