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TDA3867 Datasheet(PDF) 5 Page - NXP Semiconductors |
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TDA3867 Datasheet(HTML) 5 Page - NXP Semiconductors |
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5 / 14 page  January 1992 5 Philips Semiconductors Preliminary specification Quasi-split sound processor with two FM demodulators TDA3867T FUNCTIONAL DESCRIPTION The quasi-split sound processor is suitable for all FM standards (e. g. B/G). The AGC detector uses peak sync level. Sound carrier SC1 (5.5 MHz) provides AF1, sound carrier SC2 (5.74 MHz) provides AF2. With no sound carrier SC2 on pin 22, AF2 output is muted. The mute circuit prevents false signal recognition in the stereo decoder at high IF signal levels when no second sound carrier exists (mono) and an AF signal is present in the identification signal frequency range. With 1 mV on pin 22, under measurement conditions, AF2 is switched on (see limiting amplifier). Weak input signals at pins 27 and 28 generate noise on pin 22, which is present in the intercarrier signal and passes through the 5.74 MHz filter. Noise on pin 22 inhibits muting. No misinterpretation due to white noise occurs in the stereo decoder; when non-correlated noise masks the identification signal frequencies, which may be present in sustained tone signals. The stereo decoder remains switched to mono. The series capacitor Cs in the 38.9 MHz resonant circuit provides a notch at the sound carrier frequency in order to provide more attenuation for the sound carrier in the vision carrier reference channel. The ratio of parallel/series capacitor depends on the ratio of VC/SC frequency and has to be adapted to other TV transmission standards if necessary, according to The result is an improved “intercarrier buzz” (up to 10 dB improvement in sound channel 2 with 250 kHz video modulation for B/G stereo) or suppression of 350 kHz video modulated beat frequency in the digitally-modulated NICAM subcarrier. The picture carrier for quadrature demodulation in the intercarrier mixer is not exactly 90 degrees due to the shift variation in the integrated phase shift network. The tuning of the LC reference circuit to provide optimal video suppression at the intercarrier output is not the same as that to provide optimal intercarrier buzz suppression. In order to optimize the AF signal performance, a fine tuning for the optimal S/N at the sound channel 2 (from 5.74 MHz) may be performed with a 250 kHz square wave video modulation. C S C P fVC fSC ⁄ () 2 -C P . = Measurements at the demodulators: For all signal-to-noise measurements the generator must meet the following specifications; phase modulation errors < 0.5 degree for B/W-jumps intercarrier signal-to-noise ratio as measured with “TV demodulator AMF2” (weighted S/N) must be > 60 dB at 6 kHz sine wave modulation of the B/W-signal. Signal-to-noise ratios are measured with ∆f= ± 50 kHz deviation and fm = 1 kHz; with a deviation of ±27 kHz the S/N ratio is deteriorated by 5.3 dB. |
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