TDA6140-5X

By capacitive coupling, the FM modulated satellite IF-signal TDA6140-5X is fed into the input of a symmetrical limiter amplifier. Asymmetrical operation of this limiter amplifier is also possible, if one of the two inputs is blocked against high frequency signals. The output signal of the amplifier TDA6140-5X is divided by four and sent directly as well as phase shifted to the quadrature demodulator. The phase shifting is done using an external LC tank circuit. The demodulated video signal is amplified and available on the video output.

The AFC stage detects frequency offsets. The output signals of the AFC stage TDA6140-5X are available at the AFC "up" and AFC "down" control pins as an information to be processed in a microprocessor. A channel-dependent offset of the AFC curve can be adjusted by an external DC-voltage of TDA6140-5X applied to the "AFC offset voltage" input pin. The AFC window width can be adjusted in the range of 0.5 to 1.5 MHz by means of an external resistance.

The information for the field strength of the FM modulated IF satellite signal TDA6140-5X is available as a DC voltage at the AGC-output. The AGC-threshold can be adjusted by a potentiometer.

The polarity of the demodulated video signal TDA6140-5X can be inverted by an external switching voltage fed into the polarity switch input pin (positive or negative modulation).