TSH512 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TSH512' PDF : 32 Pages View PDF
TSH512
General description
5.7
VCO section: voltage-controlled oscillator
Each TSH512 transmitter has its own oscillator to generate the carrier. The audio signal is
applied to the varicap diode to perform the frequency modulation. Thanks to the VCO-BIAS
voltage reference, the DC bias of the varicap is stabilized. The high power supply rejection
ratio (PSRR) of the VCO-BIAS ensures good immunity with the noise of the power supply.
Figure 33. VCO schematics
The generated frequency can be set from 400 kHz to 11 MHz by external components.
Refer to Table 1 for the usual frequencies in infrared audio.
The working frequency is:
fVCO
=
---------------1-----------------
2π (L ⋅ Ct )
where Ct is the total capacity of CL, Cp, Cs and Cv:
Ct = 1/(1/Cc+1/CL) with Cc = Cp+1/(1/Cv+1/Cs)
It is possible to use varicap diodes SMV1212 (Alpha Ind.) or ZC833 (Zetex).
Table 5.
Usual infrared frequencies
IR frequency in MHz
1.6
1.7
2.3
2.8
Applications
AM mono
FM mono
FM right channel
FM left channel or mono
The output level of the VCO can be reduced by adding the resistor RVCO between pin 19
and pin 20 or between pin 36 and pin 37 for TX1 and TX2 respectively.
Doc ID 8120 Rev 7
25/31
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