TSH512C View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TSH512C' PDF : 32 Pages View PDF
General description
5
General description
TSH512
The TSH512 is a 0.4- to 11-MHz dual FM analog transmitter. This circuit offers the functions
needed for an advanced infrared STEREO transmitter. The access pins for each section
allow high versatility and therefore a lot of applications: mono infrared transmitter, stereo
transmitter, mono/stereo sub-carrier generator for video transmissions (for example the
popular 2.4 GHz video links). The block diagram for the TSH512 is shown in Figure 1 on
page 4.
Each audio input is amplified with a low noise amplifier (LNA section) allowing connection
to line level sources or directly to a microphone. Built-in MIC BIAS voltage references
provide bias for electret condenser microphones (ECM) with a high power supply rejection
ratio.
Each audio path also includes an automatic level control (ALC) to limit the over-
modulation and the distortion on very high signal amplitudes. The following operational
amplifier (PEA) allows a pre-emphasis transfer function before modulating the varicap
diode.
Built-in voltage references (VCO-BIAS) offer a regulated voltage to bias the varicap diodes.
The voltage controlled oscillator (VCO) is an integrated oscillator giving typically 600 mV
peak-to-peak at 2.8 MHz.
The output buffer section linearly amplifies the FM carrier to provide a sinusoidal output.
This sinusoidal signal reduces the inter-modulation products between the carriers,
especially in two-way or in multi-carrier systems (see Section 4: Application information on
page 14).
The voice operated transmit function (VOX) automatically detects when an audio signal
appears over the background noise.
The standby of the second transmitter reduces consumption in mono operation.
5.1
LNA section: low noise amplifier
For each transmitter, the audio source is connected to the LNA. The LNA stage is a low
noise operational amplifier typically usable with a gain from 0 to 40 dB.
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Doc ID 8120 Rev 7
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