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TDA9874A Folha de dados(PDF) 9 Page - NXP Semiconductors |
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TDA9874A Folha de dados(HTML) 9 Page - NXP Semiconductors |
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9 / 68 page  1999 Dec 03 9 Philips Semiconductors Preliminary specification Digital TV sound demodulator/decoder TDA9874A handbook, full pagewidth 1 2 3 4 5 6 7 8 9 10 11 33 32 31 30 29 28 27 26 25 24 23 TDA9874AH MHB586 SCK WS SDO SDA VDDA3 VSSA3 CRESET SIF1 Vref1 SIF2 OUTL OUTR VDDA1 VSSA1 VSSD1 VDDD1 n.c. TP2 TP1 SCL VSSD2 NICAM Fig.3 Pin configuration (QFP44). 6 FUNCTIONAL DESCRIPTION 6.1 Description of the demodulator and decoder section 6.1.1 SIF INPUT Two input pins are provided, SIF1 and SIF2. For higher SIF signal levels the SIF input can be attenuated with an internal switchable −10 dB resistor divider. As no specific filters are integrated, both inputs have the same specification giving flexibility in application. The selected signal is passed through an AGC circuit and then digitized by an 8-bit ADC operating at 24.576 MHz. 6.1.2 AGC The gain of the AGC amplifier is controlled from the ADC output by means of a digital control loop employing hysteresis. The AGC has a fast attack behaviour to prevent ADC overloads, and a slow decay behaviour to prevent AGC oscillations. For AM demodulation the AGC must be switched off. When switched off, the control loop is reset and fixed gain settings can be chosen; see Table 16. The AGC can be controlled via the I2C-bus; details are given in Sections 10.3.2, 10.3.3 and 10.4.6. 6.1.3 MIXER The digitized input signal is fed to the mixers, which mix one or both input sound carriers down to zero IF. A 24-bit control word for each carrier sets the required frequency. Access to the mixer control word registers is via the I2C-bus (see Sections 10.3.5 and 10.3.6) or via Easy Standard Programming (ESP, see Section 10.3.23). When receiving NICAM programs, a feedback signal is added to the control word of the second carrier mixer to establish a carrier-frequency loop. 6.1.4 FM AND AM DEMODULATION An FM or AM input signal is fed through a switchable band-limiting filter into a demodulator that can be used for either FM or AM demodulation. Apart from the standard (fixed) de-emphasis characteristic, an adaptive de-emphasis is available for Wegener-Panda 1 encoded satellite programs. |
Nº de peça semelhante - TDA9874A |
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Descrição semelhante - TDA9874A |
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