Attached is the sample project for Downmixer. This project uses UAB based custom Component. PSoC Creator 3.3 CP3 (link below) to be used for testing the project.
DownMixer.cydsn.zip 2.0 MB
This is schematic of a simple BPSK modulator / demodulator assembled from a simple Opamp or PGA with G=1. To perform correctly, the input signal needs to be centered across virtual analog ground (typically VDDA/2), then the output is also centered around it. When AMux switch is closed, the Modulator gain is -1, and when it is open the gain is +1. The AMux switch needs to be connected to the Virtual GND or simply to a capacitor (which will automatically average around the middle of the input signal). Such circuit can perform both like modulator or demodulator.
You can find detailed explanation of the modulator circuit operation here (approx at 14:00):