tda6621 Infineon Technologies Corporation, tda6621 Datasheet - Page 5

• Manufacturer Part Number: tda6621
• Description: Tv-stereocoder
• Manufacturer: Infineon Technologies Corporation

Circuit Description
Matrix
The audio matrix 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 is generated and fed to the tone 1 output, the right AF-Signal is switched
to tone 2 output.
Pilottone Generator
The pilottone generator 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 is available for filtering the pilottone harmonics and for level
matching.
The status control of the stereocoder happens via two TTL compatible control inputs.
The truth table of the control inputs:
Mono mode
Stereo mode
Dual mode
Not allowed
Semiconductor Group
Stereo
Control
0
1
0
1
Dual
Control
0
0
1
1
5
Tone 1
Output
Mono
(L+R)/2
Tone 1
–
Tone 2
Output
Mono
R
Tone 2
–
Pilottone
Mod.
Not mod.
117 Hz
274 Hz
–
TDA 6621