SGS Thomson Microelectronics ST7537HS1 Datasheet

.

HALF DUPLEX ASYNCHRONOUS 2400bps
FSK MODEM

.

Tx CARRIER FREQUENCY SYNTHESIZED
FROM EXTERNAL CRYSTAL

.

LOW DISTORTION Tx SIGNAL

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Rx SENSITIVITY BETTER THAN 1mV

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CARRIER DETE CT ION

.

WATCH-DOG INPUT

.

RESET AND MASTER CLOCK OUTPUTS
FOR MICROCONTRO LLER

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POWER AMPLIFIER BIAS CURRENT CON­TROL (HIGH IMPEDANCE IN Rx MODE)

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SIMPLE AND ECONOMICAL APPLICATION
SCHEMATICS

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COMPATIBLE WITH CENELEC EN 50065-1
AND FCC SPECIFICATION

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CARRIER DETECT CLAMPING ON RxD
PROGRAMMABLE (ALLOWING DEMODULA­TION ON VERY LOW RECEIVE LEVEL,
1mV

TYPICAL LY)

RMS

RMS

ST7537HS1

HOME AUT O MATION MO DE M

PLCC28

(Plastic Chip Carrier)

ORDER CODE : ST7537HS1

DESCRIPTIO N

The ST7537HS1 is a half duplex asynchronous
FSK MODEM designed for home automation com­munication on the domestic electric mains which
complies with the EN 50065-1 CENELEC stand­ard.

It mainly operates from a 10V power supply and a
5V power supply for the microcontroller digital in­terface.

It is interfaced to the power line by an external
driver, and a transformer (see Application Sche­matic Diagram). Its data transmission rate is
2400 bps and its carrier frequency is 132.45kHz.

June 1995

PIN CONNECTIONS

RxFO

RAI

3

4

TxIFI

PAFB

ATO

PABC

PABC
TEST1
TEST2

5

6
7

8
9

10
11

12

TEST3

13

TEST4

AV

DV

DD

2

14

DD

V

DV

CM

1

15

SS

AV

XTAL1

28

16

SS

DEMI

IFO

26

27

25

DV

CC

24

RSTO

23

RxD

22

TxD

21

CD

20

Rx/Tx

19

WD

18

17

MCLK

XTAL2

7537H-01.EPS

1/9

ST7537HS1

PIN DESCRIPTION

Pin

Name

V

CM

AV

DD

RAI 3 Analog Receive Analog Input

RxFO 4 Analog Receive Filter Output

TxIFI 5 Analog Transmit and Intermediate Frequency Filters Test Input (mode TEST3)

PAFB 6 Analog Power Amplifier Feed-back Input

ATO 7 Analog Analog Transmit Output
PABC 8 Digital (10V) Power Amplifier Bias Current Control Complementary Output
PABC 9 Digital (10V) Power Amplifier Bias Current Control Output

TEST1 10 Digital Tx to Rx Automatic Mode Switching Control Input
TEST2 11 Digital Automatic Mode Switching Time and Watch-dog Time Reduction Control Input
TEST3 12 Digital TxIFI Selection Input
TEST4 13 Digital Undelayed Reset Input

DV

DD

DV

SS

XTAL1 16 Digital (10V) Crystal Oscillator Input
XTAL2 17 Digital (10V) Crystal Oscillator Output

MCLK 18 Digital Master Clock Output

WD 19 Digital Watch-dog Input

Tx 20 Digital Rx or Tx Mode Selection Input

Rx/

CD 21 Digital Carrier Detect Output

TxD 22 Digital Transmit Data Input

RxD 23 Digital Receive Data Output
RSTO 24 Digital Reset Output

DV

CC

IFO 26 Analog Intermediate Frequency Filter Output
DEMI 27 Analog Demodulator Input
AV

SS

Pin

Number

Pin

Type

1 Analog Common Mode Voltage
2 Supply Analog Power Supply : 10V ±5 %

14 Supply Digital Power Supply : 10V ±5%
15 Supply Digital Ground : 0V

25 Supply Digital Buffers Supply Voltage : 5V ±5 %

28 Supply Analog Ground : 0V

Description

7537H-01.TBL

2/9

BLOCK DIAG RAM

AV

DD

2 14 28 15 1 25

DV

DD

AV

DV

SS

SS

V

CM

DV

ST7537HS1

CC

RAI

RxFO

CD

ATO
PAFB
PABC
PABC

RxD

3

4

21

7
6
9
8

23

TEST1 TEST2 TEST3 TEST4

Rx BAND-PASS

A.A.

FILTER

CARRIER

DETECTION

OUTPUT

AMPLIFIER

TEST LOGIC

S.C. FILTER

SMT.

FILTER

SMT.

FILTER

REFERENCE

Tx BAND-PASS

S.C. FILTER

13121110

20dB GAIN

VOLTAGE

TRANSMIT SECTION

The transmit mode is set when Rx/

Tx = 0, if R x/Tx
is held at 0 longer than 1 second, then the device
switches automatically in the Rx mode. A new
activation of the Tx mode requires Rx/

Tx to be
returned to 1 for a minimum 2 microsecond period
before being set to 0.

The Transmit Data (TxD) enter asynchronously the
FSK modulator with a nominal intra-message data
rate of 2400 bps.

The basic transmit frequencies are :

- f(TxD=0) = 133.05kHz

- f(TxD=1) = 131.85kHz
These frequencies are synthesized from a

11.0592MHz crys tal oscillator; their precis ion is the
same as the crystal one’s (100ppm).

The modulated signal coming out of the FSK modu­lator is filtered by a switched-capacitor band-pass
filter (Tx band-pass) in order to limit the output
spectrum and to reduce the level of harmonic com­ponents.

The final stage of t he Tx path co nsists of an opera­tional amplifier which needs a feed-back signal
(PAFB) from the power amplifier as shown on
Application Schematic Diagram.

In Tx mode the Rec eive Data (R xD) signa l is set to 1.

MUX

POST-DEMO

S.C. FILTER

MUX

A.A. FILTER

A.A. FILTER

CORRELATOR

FSK DEMODULATOR

I.F. BAND-PASS

S.C. FILTER

MODULATOR

SMT.

FILTER

TIME BASE

RESET LOGIC

CONTROL LOGIC

FSK

IFO

26

17

XTAL2

16

XTAL1

18

MCLK

19

WD

24

RSTO

20

Rx/Tx

22

TxD

TxIFI

5

27

DEMI

ST7537HS1

RECEIVE SECTION

The receive section is active when Rx/

Tx = 1.

The Rx signal is applied on RAI and filtered by a
band-pass switched capacitor filter (Rx b and-pass)
centered on the carrier frequency and whose band­width is around 12kHz.

The Rx filter output is amplified by a 20dB gain
stage which provides symetrical limitations for
large voltage. The resulting signal is down-con­verted by a mixer which receives a local oscillator
synthesized by the FSK modulator block. Finally an
intermediate frequency band-pass filter (IF band­pass) whose central frequency is 5.4k Hz improves
the signal to noise ratio before entering the FSK
demodulator.

The coupling of the intermediate frequency filter
output (IFO) to the FSK demodulator input (DE MI)
is made by an external capacitor C5 (100nF ±10%,
10V) which cancels the Rx path offset voltage.

The RxD output delivers the demodulated signal if
the carrier detect (
high level when

CD) signal is low and is set to

CD = 1.

The RxD output can delivers the demodulated
signal whatever the lev el of

CD (0 or 1) if R x/Tx = 1

and TxD = 0 (see Figure 1).

7537H-02.EPS

3/9