TSH511

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ate the fade-in and fade-out control ramps for the

audio buffers. The Squelch has been designed

with particular attention to avoid audio pop-noise.

Figure 6 : Squelch schematic

The squelch section is driven by the receiver RX1

but controls both audio buffers.

Audio Buffer sections

The audio signal from a FM demodulator enters

into the 6dB/octave low-pass filter for de-empha-

sis. 50µs and 75µs are standard de-emphasis val-

ues.

After the de-emphasis network, the potentiometer

controls the volume.

The Rail-to-Rail output stage of each Audio Buffer

is able to drive 20 mW into 16

voltage. In this condition, the distortion is typically

0.3% before saturation.

The Audio Buffers can also drive the other usual

impedances used in audio: 32

(see the corresponding distorsion curves).

The high input impedances of the Audio Buffers

reduce the coupling capacitors to less than 0.1 µF

allowing space and cost saving.

Standby section

Depending on the states of the logic inputs SBY1

and SBY2, RX2 and the Audio Buffer2 can be

disabled separately. The TSH511 receiver can

adapt to different applications by using SBY1 &

SBY2 standby pins:

In the standard stereo mode, the configuration is:

SBY1 = SBY2 = ’Low’

In mono mode with one load(example: a single

loadspeaker), RX2 and Audio Buffer 2 are

disabled, the configuration is SBY1 = SBY2 =

’High’.

In mono mode with a stereo load (example: a

stereo headphone), the configuration is SBY1 =

’high’, SBY2 = ’Low’.

A pin connected to Vcc is at ’High’ state, and if

connected to GND is at ’Low’ state.

SBY1

pin 32

SBY2

pin 31

RX1 &

audio

buffer1

RX2

audio

buffer 2

typical

use

Low

Low

ON

ON

ON

stereo

Low

High

High

Low

ON

OFF

ON

mono on

the two

outputs

High

High

ON

OFF

OFF

mono on

one out-

put