TSH511CFT datasheet(14/18 Pages) STMICROELECTRONICS

14 / 18 page

TSH511

14/18

GENERAL DESCRIPTION

The TSH511 is a 0.4 to 11 MHz dual FM analogue

receiver. The incoming signal is amplified with a

22 dB Low Noise Amplifier (LNA section). The

good noise performance of the LNA allows the

photodiode for infrared applications to be connect-

ed directly to the TSH511 without any external

preamplifier. The access pins for each section and

the two standby configurations allow a high versa-

tility for many applications: HiFi stereo infrared re-

ceiver, mono/stereo subcarrier receiver, power

line carrier audio.

Figure 1 : TSH511 block diagram

The LNA is common to both receivers but the out-

put is split in two: one for each receiver. Each LNA

output can be connected to a first optional filter for

bandpass or reject filtering.

The filtered signal is amplified with an intermedi-

ate Amplifier (AMP section) followed by a second

filter. The AMP sections have 20 dB typical gain.

Finally, the signal is amplified and limited in the

Limiter (LIM section). The 60 dB amplifier-limiter

LIM provides a constant amplitude signal to the

demodulator. It reduces AM parasitics demodula-

tion in the FM demodulator.

The FM demodulator is a classical quadrature de-

tector using an external tank.

The demodulated signal can be amplified by the

Audio Buffer section after de-emphasis. Each Au-

dio Buffer can drive a 16 ohms headphone with 20

mW power.

The two standby pins SBY1 & SBY2 allow the sec-

ond receiver RX2 to be put into standby for mono

operation. In mono, it is possible to use both Audio

Buffers or only one depending on the combination

on SBY1 & SBY2.

To avoid noise at the audio output, a Squelch sec-

tion mutes the Audio Buffers when no carrier is re-

ceived. The Squelch Section uses the demodulat-

ed signal of the first receiver (RX1). This signal is

highpass filtered, rectified and compared to a

threshold to produce the Mute signal (pin 25).

When no carrier is received on RX1, the wideband

’FM noise’ on the demodulator increases and the

Mute signal mutes the both Audio Buffers. When

the carrier is present, the wideband noise on the

demodulator output decreases, enabling the Au-

dio Buffers.

Figure 2 : Infrared audio frequencies

LNA section: Low Noise Amplifier

The Low Noise Amplifier (LNA) has a typical gain

of 22 dB to amplify the incoming RF signal from

the photodiode. The LNA is common to both re-

ceivers sections RX1 and RX2.

Figure 3 : LNA schematic

BUF-OUT2

BUF-OUT1

MUTE-OUT

MUTE-INT

TSH511

Audio

buffers

Standby

RX1

RX2

SQUELCH

GND

SBY1

SBY2

VCC

DEC-OUT

GND

MUTE-IN

GND

AMP-IN2

VCC

LNA-OUT2

VCC

LNA-IN

GND

LNA-OUT1

VCC

AMP-IN1

DEC-LNA

Vref

LNA

amp.

limiter

FM demodulator

limiter

amp.

FM demodulator

BUF-OUT2

BUF-OUT1

MUTE-OUT

MUTE-INT

TSH511

Audio

buffers

Standby

RX1

RX2

SQUELCH

GND

SBY1

SBY2

VCC

DEC-OUT

GND

MUTE-IN

GND

AMP-IN2

VCC

LNA-OUT2

VCC

LNA-IN

GND

LNA-OUT1

VCC

AMP-IN1

DEC-LNA

Vref

LNA

amp.

limiter

FM demodulator

limiter

amp.

FM demodulator

IR frequency

applications

1.6 MHz

AM mono

1.7 MHz

FM mono

2.3 MHz

FM right channel

2.8 MHz

FM left channel or mono

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