TDA4480-C

The TDA4480-C allows the high quality processing of sound carrier for different TV standards. The circuit requires separate vision and audio carrier inputs. It delivers the output audio signal for mono, two channels or stereo applications. Audio carrier signal (simple or double carrier, FM and AM) is applied via three stage AGC controlled broad band amplifier which delivers regulated output signal for two mixing stages.

One mixer works for AM-demodulation and AGC-function whereas the second mixer TDA4480-C produces the sound intercarrier IF-frequencies (5.5/5.74 MHz). Vision carrier signal for the intercarrier generation is delivered from the demodulator tank of the video IF circuit (TDA 4439, TDA 4453). It is then matched via a limiter stage to the FM intercarrier mixer. FM-sound-IF-carrier reaches the quadrature demodulator via the selection circuit and the following limiter amplifier. The final audio signal is supplied to the low ohmic output (Pin 7,14) with low pass filter character.

There is a switchable TDA4480-C converter for different audio standards (4.5, 6.00 and 6.5 MHZ), which mixes the sound 1P-signal properly e.g. at 5.5 MHz. The VC0 (Pin 10) must be controlled across the sound output (Pin 7) which includes AFC-function. Sound signal at the AM-modulation is introduced via standard switch in the first sound channel, whereas the intercarrier, converter section and both FM demodulators are switched off. In case of sound IF converter operation, the second sound channel and the AM-section are switched off. The standard mode is controlled by a tristate signal on Pin 6.