STV0042A datasheet(3/24 Pages) STMICROELECTRONICS

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PIN DESCRIPTION

1 - Sound Detection

FMIN

This is the input to the two FM demodulators. It

feeds two AGC amplifiers with a bandwidth of at

least 5-10MHz. There is one amplifier for each

channel both with the same input. The AGC ampli-

fiers have a 0dB to +40dB range.

ZIN =5k

Ω, Min input = 2mVPP per subcarrier.

Max input = 500mVPP (max when all inputs are

added together, when their phases coincide).

AGC L, AGC R

AGC amplifiers peak detector capacitor connec-

tions. The output current has an attack/decayratio

of 1:32. That is the ramp up current is approxi-

mately 5

µA and decay current is approximately

160

µA. 11V gives maximum gain. These pins are

also driven by a circuit monitoring the voltage on

AMPLK L and AMPLK R respectively.

AMPLK L, AMPLK R

The outputs of amplitude detectors LEFT and

RIGHT. Each requires a capacitor and a resistor to

GND. The voltage across this is used to decide

whether there is a signal being received by the FM

detector. The level detector output drives a bit in

the detector I

2C bus control block.

AMPLK L and AMPLK R drive also respectively

AGC L and AGC R. For instance when the voltage

on AMPLK L is > (VREF +1 VBE) it sinks current to

VREF from pin AGCL to reduce the AGC gain.

DET L, DET R

Respectively the outputs of the FM phase detector

left and right. This is for the connection of an

external loop filter for the PLL. The output is a

push-pull current source.

CPUMP L, CPUMP R

The output from the frequency synthesizer is a

push-pullcurrent source which requiresa capacitor

to ground to derive a voltage to pull the VCO to the

target frequency. The output is

±100µA to achieve

lockand

±2µAduringlock to providea trackingtime

constant of approximately 10Hz.

VREF

This is the audio processor voltage reference used

through out the FM/audio section of the chip. As

such it is essential that it is well decoupled to

ground to reduce as far as possible the risk of

crosstalk and noise injection. This voltage is de-

rived directly from the bandgap reference of 2.4V.

The VREF output can sink up to 500

µA in normal

operation and 100

µA when in stand-by.

IREF

This is a bufferedVREF outputto an off-chip resistor

to produce an accurate current reference, within

the chip, for the biasing of amplifiers with current

outputs into filters. It is also required for the Noise

reduction circuit to provide accurate roll-off fre-

quencies.

This pin should not be decoupled as it would inject

current noise. The target current is 50

µA ±2% thus

a 47.5k

Ω ±1% is required.

A 12V

Double bonded main power pin for the audio/FM

section of the chip. The two bond connections are

to the ESD and to power the circuit and on chip

regulators/references.

A GND L

This ground pin is double bonded :

1) to channel LEFT : RF section & VCO,

2) to both AGC amplifiers, channel LEFT and

RIGHT audio filter section.

A GND R

This ground pin is double bonded :

1) to the volume control, noise reduction system,

ESD + Mux + VREF

2) to channel right : RF section & VCO

2 - Baseband Audio Processing

PK OUT

The noise reduction control loop peak detector

output requires a capacitor to ground from this pin,

and a resistor to VREF pin to give some accurate

decaytime constant.An on chip5k

Ω ±25 % resistor

and external capacitor give the attack time.

PK IN

This pin is an input to a control loop peak detector

and is connectedto the output of the offchip control

loop band pass filter.

SUM OUT

The two audio demodulated signals are summed

together by means of an amplifier with a gain of 0.5.

If both inputs are 1V then the output is 1V. This

amplifier has an input follower buffer which gives a

VBE offset in the DC bias voltage. Thus the filter

which this amplifier drives must include AC cou-

pling to the next stage (PK IN Pin).

FC L, FC R

The variable bandwidth transconductance ampli-

fier has a current output which is variable depend-

ing on the input signal amplitude as defined by the

control loop of the noise reduction. The output

current is then dumped into an off-chip capacitor

which together with the accurate current reference

define the min/max rolloff frequencies.A resistor in

series with a capacitor is connected to ground from

these two pins.

STV0042A

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