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TDA9840T 数据表(PDF) 7 Page - NXP Semiconductors |
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TDA9840T 数据表(HTML) 7 Page - NXP Semiconductors |
7 / 28 page 1998 Jul 03 7 Philips Semiconductors Product specification TV and VTR stereo/dual sound processor with digital identification and I2C-bus control TDA9840 FUNCTIONAL DESCRIPTION The TDA9840 (see Fig.1) receives the signals from the FM-demodulators in a TV two sound-carrier system. The circuit is realized by the H00485 bipolar process. The IC is intended for use in economic TV and VTR receivers. Therefore optimum relationship between integration of functions and use of external components has been striven for. Additionally a new type of identification circuit has been developed. AF signal handling The input AF signals, derived from the two sound carriers, are processed in analog form using operational amplifiers.The circuit incorporates level- and stereo-adjustment to correct the spreading in the FM detector output levels. Dematrixing uses the technique of two amplifiers processing the AF signals. Finally, a source selector provides the facility to route the mono signal through to the outputs (‘forced mono’). De-emphasis is performed by two RC low-pass filter networks with internal resistors and external capacitors. This provides a frequency response with the tolerances given in Fig.4. A source selector, controlled via the I2C-bus, allows selection of the different modes of operation in accordance with the transmitted signal. The device was designed for a nominal input signal (FM: 54% modulation is equivalent to ∆f= ±27 kHz / AM: m = 0.54) of 250 mV RMS (Vi1,Vi2), respectively 500 mV RMS (Vi3,Vi4). A nominal gain of 6 dB for Vi1 and Vi2 signals and 0 dB for Vi3 and Vi4 signals is built-in. By using rail-to-rail operational amplifiers, the clipping level (THD ≤1.5%) is 1.6 V RMS for VP = 5 V and 2.65 V RMS for VP = 8 V at outputs Vo1, Vo2,Vo3 and Vo4. Care has been taken to minimize switching plops. Also total harmonic distortion and random noise are considerably reduced. Identification The pilot signal is fed via an external RC high-pass filter and single tuned LC band-pass filter to the input of a gain controlled amplifier. The external LC band-pass filter in combination with the external RC high-pass filter should have a loaded Q-factor of about 40 to 50 to ensure the highest identification sensitivity. By using a fixed coil ( ±5%) to save the alignment (see Fig.2), a Q-factor of about 12 is proposed. This may cause a loss in sensitivity of about 2 to 3 dB. A digital PLL circuit generates a reference carrier, which is synchronized with the pilot carrier. This reference carrier and the gain controlled pilot signal are fed to the AM-synchronous demodulator. The demodulator detects the identification signal, which is fed through a low-pass filter with external capacitor CLP (pin 3) to a Schmitt-trigger for pulse shaping and suppression of low level spurious signal components. This is a measure against mis-identification. The identification signal is amplified and fed through an AGC low-pass filter with external capacitor CAGC (pin 2) to obtain the AGC voltage for controlling the gain of the pilot signal amplifier. The identification stages consist of two digital PLL circuits with digital synchronous demodulation and digital integrators to generate the stereo or dual sound identification bits which can be read out via the I2C-bus. A 10 MHz quartz crystal oscillator provides the reference clock frequency. The corresponding detection bandwidth is larger than ±50 Hz for the pilot carrier signal, so that fp-variations from the transmitter can be tracked in case of missing synchronisation with the horizontal frequency fH. However the detection bandwidth for the identification signal is made small (approximately ±1 Hz) to reduce mis-identification. Figure 2 shows an example of the alignment-free fp band-pass filter. To achieve the required QL of approximately 12, the Q0 at fp of the coil was chosen to be approximately 25 (effective Q0 including PCB influence). Using coils with other Q0, the RC-network (RFP,CFP) has to be adapted accordingly. It is assumed that the loss factor tan δ of the resonance capacitor is ≤0.01 at fp. Copper areas under the coil might influence the loaded Q and have to be taken into account. Care has also to be taken in environments with strong magnetic fields when using coils without magnetic shielding. I2C-bus transceiver The complete IC is controlled by a microcomputer via the I2C-bus. The built-in I2C-bus transceiver transmits the identification result to the I2C-bus and receives the control data for the source selector and level control. The I2C-bus protocol is given in Tables 2 to 12 respectively. The data transmission between the microcontroller and the other I2C-bus controlled ICs is not disturbed, when the supply voltage of the TDA9840 is not connected or when powering up or down. Finally, a Schmitt-trigger is built-in the SDA/SCL interface to suppress spikes from the I2C-bus. |
类似零件编号 - TDA9840T |
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类似说明 - TDA9840T |
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