OM5610 查看數據表（PDF） - Philips Electronics

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OM5610

Matchbox global FM tuner

Philips Electronics 

Philips Semiconductors

Matchbox global FM tuner

Preliminary specification

OM5610

PINNING

PIN

1

2

3

4

5

6

7

8

9

10

11

12

DESCRIPTION

ground

ground

WREN

CLCK

STEREO

DATA

supply voltage (+5 V)

supply voltage (+12 V)

audio right output

ground

audio left output

MPX-RDS

FUNCTIONAL DESCRIPTION

The OM5610 is an integrated FM stereo radio circuit

including digital tuning and control functions.

The radio

The radio circuit incorporates a tuned RF stage, a double

balanced mixer, a one-pin oscillator and is designed for

distributed IF ceramic filters. The FM quadrature detector

uses a ceramic resonator.

The PLL stereo decoder incorporates a signal dependent

stereo-blend circuit and a soft-mute circuit.

Tuning

The tuning-concept of Self Tuned Radio (STR) is based on

FUZZY LOGIC: it mimics hand tuning (hand tuning is a

combination of coarse and fine tuning to the qualitatively

best frequency position). As a consequence the tuning

system is very fast.

The tuning algorithm, which is controlled by a sequential

circuit, is completely integrated; so there are only a few

external components needed.

The bus and the microcontroller can be kept very simple.

The bus only consists of three wires (CLCK, DATA and

WREN). The microcontroller must basically give two

instructions:

• Preset operation

• Search operation.

PRESET OPERATION

In preset mode, the microcontroller has to load information

such as frequency band, frequency and mono/stereo. This

information has to be sent via the bus to the tuner.

The internal algorithm controls the tuning sequence as

follows:

1. The information is loaded into a shift register, a

last-station memory and the counter.

2. The Automatic Frequency Control (AFC) is

switched-off.

3. The counter starts counting the frequency and the

tuning voltage is varied until the real frequency roughly

equals the desired frequency.

4. The AFC is then switched on and the real frequency is

more precisely tuned to the actual IF frequency.

5. After the AFC has tuned the real frequency to the

desired frequency an in-lock signal is generated; then

the counter is switched off. In order to get a reliable

in-lock signal, there are two parameters measured: the

field strength and the S-curve.

6. The field strength indicates the strength of the station

and by looking at the S-curve the system can detect an

in-lock situation.

In the event of fading or pulling the in-lock signal becomes

logic 0 and the synthesizer will be switched on again

(maintaining last station) and the algorithm will be

repeated.

SEARCH OPERATION

During a search operation, the only action the

microcontroller has to take is: sending the desired band

plus the direction and the search sensitivity level to the

tuner. The search operation is performed by the charge

pump until an in-lock signal is generated (combination of

measuring the field strength and the S-curve). By looking

at the S-curve the system can distinguish false in-locks

from real in-locks (false in-locks occur on the wrong slope

of the S-curve). The AFC then fine tunes to the station.

The frequency of the found station will be counted by the

counter and written into the last-station memory and the

shift register of the counter. At this time the frequency is

available in the shift register and can be read by the

microcontroller. The microcontroller decides whether the

frequency is within the desired frequency band. If so, this

frequency can be stored under a preset and if not, a new

search action should be started.

1997 Apr 25

3

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