TDA9806 查看數據表（PDF） - Philips Electronics

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TDA9806

Multistandard VIF-PLL and FM-PLL demodulator

Philips Electronics 

Philips Semiconductors

Multistandard VIF-PLL and

FM-PLL demodulator

Preliminary specification

TDA9806

FM detector

The FM detector consists of a limiter, an FM-PLL and an

AF amplifier. The limiter provides the amplification and

limitation of the FM sound intercarrier signal before

demodulation. The result is high sensitivity and AM

suppression. The amplifier consists of 7 stages which are

internally AC-coupled in order to minimize the DC offset

and to save pins for DC decoupling.

The FM-PLL consists of an integrated relaxation oscillator,

an integrated loop filter and a phase detector. The

oscillator is locked to the FM intercarrier signal, output

from the limiter. As a result of locking, the oscillator

frequency tracks with the modulation of the input signal

and the oscillator control voltage is superimposed by the

AF voltage. The FM-PLL operates as an FM-demodulator.

The AF amplifier consists of two parts:

1. The AF preamplifier for FM sound is an operational

amplifier with internal feedback, high gain and high

common mode rejection. The AF voltage from the PLL

demodulator, by principle a small output signal, is

amplified by approximately 33 dB. The low-pass

characteristic of the amplifier reduces the harmonics of

the intercarrier signal at the sound output terminal, at

which the de-emphasis network for FM sound is

applied. An additional DC control circuit is

implemented to keep the DC level constant,

independent of process spread.

2. The AF output amplifier (10 dB) provides the required

output level by a rail-to-rail output stage. This amplifier

makes use of an input selector for switching to FM

de-emphasis or mute state, controlled by the mute

switching voltage.

Internal voltage stabilizer and 1⁄2VP-reference

The bandgap circuit internally generates a voltage of

approximately 1.25 V, independent of supply voltage and

temperature. A voltage regulator circuit, connected to this

voltage, produces a constant voltage of 3.6 V which is

used as an internal reference voltage.

For all audio output signals the constant reference voltage

cannot be used because large output signals are required.

Therefore these signals refer to half the supply voltage to

achieve a symmetrical headroom, especially for the

rail-to-rail output stage. For ripple and noise attenuation

the 1⁄2VP voltage has to be filtered via a low-pass filter by

using an external capacitor together with an integrated

resistor (fg = 5 Hz). For a fast setting to 1⁄2VP an internal

start-up circuit is added.

1995 Sep 05

7

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