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TEA6880H Datasheet(PDF) 10 Page - NXP Semiconductors |
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TEA6880H Datasheet(HTML) 10 Page - NXP Semiconductors |
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10 / 88 page  2000 May 08 10 Philips Semiconductors Product specification Up-level Car radio Analog Signal Processor (CASP) TEA6880H 7 FUNCTIONAL DESCRIPTION 7.1 Stereo decoder The MPX input is the null-node of an operational amplifier with internal feedback resistor. Adapting the stereo decoder input to the level of the MPX signal, coming from the FM demodulator output, is realized by the value of the input series resistor RIN. To this input a second source (AM detector output) can be fed by current addition. The input amplifier is followed by an integrated 4th order Bessel low-pass filter with a cut-off frequency of 80 kHz. It provides necessary signal delay for FM noise blanking and damping of high frequency interferences coming to the stereo decoder input. Output of this filter is fed to the soft mute control circuitry, the output is voltage to current converted and then fed to phase detector, pilot detector and pilot canceller circuits, contained in the stereo decoder PLL block. For regeneration of the 38 kHz subcarrier, a PLL is used. The fully integrated oscillator is adjusted by means of a digital auxiliary PLL into the capture range of the main PLL. The auxiliary PLL needs an external reference frequency (75.4 kHz) which is provided by the TEA6840H. The required 19 and 38 kHz signals are generated by division of the oscillator output signal in a logical circuitry. The 19 kHz quadrature phase signal is fed to the 19 kHz phase detector, where it is compared with the incoming pilot tone. The DC output signal of the phase detector controls the oscillator (PLL). The pilot presence detector is driven by an internally generated in-phase 19 kHz signal. Its pilot dependent DC output voltage is fed to a threshold switch, which activates the pilot indicator bit and turns the stereo decoder to stereo operation. The same DC voltage is used to control the amplitude of an anti-phase internally generated 19 kHz signal. In the pilot canceller, the pilot tone is compensated by this anti-phase 19 kHz signal. The pilot cancelled signal is fed to the matrix. There, the side signal is demodulated and combined with the main signal to left and right audio channel. Compensation for roll-off in the incoming MPX signal caused by IF filters and FM demodulator is typically realized by an external compensation network at pin 57, individual alignment is achieved by I2C-bus controlled amplification of the side signal (DAA). A smooth mono to stereo takeover is achieved by controlling the efficiency of the matrix with help of the SNC peak detector. The matrix is followed by the FM noise suppression gates, which are combined with FM single poles and High Cut Control (HCC). The single pole is defined by internal resistors and external capacitors. From the gate circuits audio is fed to the switchable de-emphasis, where the demodulated AM stereo signal can be fed in. After de-emphasis the signal passes to the output buffers and is fed to the radio input of the source selector. For HCC, the time constant of the single pole contained in the output buffer can be changed to higher values. This function is controlled by an average detector contained in the multipath and fading detector. 7.2 FM noise blanker The input of the ignition noise blanker is coupled to the MPXRDS (pin 55) input signal and to the IF level input (pin 3). Both signals are fed via separate 120 kHz filters and rectifiers to an adder circuit. The output signal of the adder circuit is fed in parallel to the noise detector and the interference detector. The noise detector is a negative peak detector. Its output controls the trigger sensitivity (prevention to false triggering at noisy input signals) and the gain of the MPX high-pass filter. The output of the interference detector, when receiving a steep pulse, fires a monoflop, contained in the pulse former circuitry. The time constant of the monoflop is defined by an internal capacitor and its output activates the blanking gates in the audio. 7.3 AM noise blanker The AM noise blanking pulse is derived from the AM audio signal which is fed into pin 53 with the help of a peak-to-average comparator. The blanking time is set by a pulse former with external capacitor. The blanking pulse is fed to the gate in the AM audio path and out to pin AMHOLD to operate the gate built into the external AM stereo processor. 7.4 Multipath/fading detection and weak signal control For FM signal quality dependent controls there is built-in a combination of six detectors driven by the level information direct, by the AC components on the level via a 20 kHz band-pass filter (AM wideband) or the high notes present at the FM demodulator output via a 60 kHz high-pass filter (ultrasonic noise). The relation between DC level and the AC components is programmable by the I2C-bus (2 bits each). Output of level buffer, AM wideband detector and ultrasonic noise detector are analog-to-digital converted and readable by the I2C-bus. |
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Descripción similar - TEA6880H |
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