TDA5101A Datasheet, PDF (13/21 Pages) Infineon Technologies AG – ASK Transmitter 315 MHz

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TDA 5101A
Preliminary
Functional Description
3.4 Functional Blocks
1. PLL Synthesizer
The Phase Locked Loop synthesizer consists of a voltage controlled oscillator
(VCO), an asynchronous divider chain, a phase detector, a charge pump and a
loop filter and is fully implemented on chip. The tuning circuit of the VCO con-
sisting of spiral inductors and varactor diodes is on chip, too. Therefore no
additional external components are necessary. The nominal center frequency
of the VCO is 630 MHz. The oscillator signal is fed both to the synthesizer
divider chain and to the power amplifier. The overall division ratio of the asyn-
cronous divider chain is 64. The phase detector is a Typ IV PD with charge
pump. The passive loop filter is realized on chip.
2. Crystal Oscillator
The crystal oscillator operates at a frequency of 9.84 MHz. It achieves a turn
on time of typically less than 1ms. To attend this, a NIC oscillator type is imple-
mented in the TDA 5101A.
The oscillator type has the property, that the input impedance is a negative
resistance in series to an inductance. Therefore the load capacitance of the
crystal CL (specified by the crystal supplier) is transformed to the capacitance
Cv.
-R
I
f, CL Cv
TDA 5101A
Cv = -C-----1----L-------+-1----_ω-----2---l-
CL: crystal load capacitance for nominal frequency
ω: angular frequency
l: inductivity of the crystal oscillator (typically 11µH)
The crystal oscillator signal is divided in the frequency by 4 and guided to the
open collector output CLKOUT to drive the clock input of a micro controller.
Semiconductor Group
3-5
Specification, May 1999