TEA6886 データシートの表示（PDF） - Philips Electronics

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TEA6886

Up-level Car radio Analog Signal Processor (CASP)

Philips Electronics 

Philips Semiconductors

Up-level Car radio Analog Signal

Processor (CASP)

Product specification

TEA6886HL

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 the necessary signal delay for FM noise

blanking and damping of high frequency interference at

the stereo decoder input.

The output signal of this filter is fed to the soft mute control

circuitry, the output is voltage-to-current converted and

then fed to the phase detector, pilot detector and pilot

canceller circuits, contained in the stereo decoder PLL

block. A PLL is used for regeneration of the 38 kHz

subcarrier. 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

logic circuit. 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 present 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 switches 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. The pilot tone is compensated by this anti-phase

19 kHz signal in the pilot canceller.

The pilot cancelled signal is fed to the matrix. There, the

side signal is demodulated and combined with the main

signal to the left and right audio channels. Compensation

for roll-off in the incoming MPX signal caused by the IF

filters and the FM demodulator is typically realized by an

external compensation network at pin MPXIN, 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 the 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. Audio is fed from the gate circuits 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 input signal and to the LEVEL input. 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 of

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 single-shot

trigger circuit, contained in the pulse former circuitry. The

time constant of the single-shot trigger circuit 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 AMNBIN 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 at 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 a built-in

combination of six detectors. These detectors are driven

by the level information direct, by the AC components on

the level via a 20 kHz band-pass filter (AM wideband) or by

the high notes present at the FM demodulator output via a

60 kHz high-pass filter (ultrasonic noise). The relationship

between the DC level and the AC components is

programmable by the I2C-bus (2 bits each). The output of

the level buffer, AM wideband detector and ultrasonic

noise detector are analog-to-digital converted and

readable by the I2C-bus.

2000 Nov 21

10

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