TDA6621

The audio matrix TDA6621 is generating the correct audio signals for the three possible operation modes. In mono operation the tone 1 input signal is fed to both AF outputs. In dual mode both audiosignals are appearing at both outputs. When stereo operation is selected, a (L+R)/2 signal TDA6621 is generated and fed to the tone 1 output, the right AF-Signal is switched to tone 2 output.

The pilottone generator TDA6621 consists of a PLL circuitry and an AM modulator. The PLL is locked with the 15625 Hz line frequency and is generating the unmodulated pilottone and a square wave identification tone. This identification tone has to be filtered in an external filter to a sinusoidal wave form. This is fed into the AM modulator, which generates the AM modulated pilottone. A DC control voltage is adjusting the modulation depth. A high speed OP amp TDA6621 is available for filtering the pilottone harmonics and for level matching.