ATA2745 データシートの表示（PDF） - Atmel Corporation

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ATA2745

UHF ASK Transmitter

Atmel Corporation 

3. General Description

The fully integrated VCO and the single-ended open-collector output allow particularly simple,

low-cost RF miniature transmitters to be assembled. The single-ended output enables a consid-

erably simplified adaptation of both a magnetic loop antenna of any form or a λ / 4 antenna. This

is because the load impedance must not be balanced as would be the case with a differential

output.

The XTO's frequency can be selected to be either 13.56 MHz or 9.844 MHz (USA). At these fre-

quencies, crystals have a very fast start-up time (< 1.5 ms), whereby a wait time of 5 ms to

10 ms is required until the transmitter IC is locked. This means that the processor does not need

to poll a lock detect output.

4. Functional Description

4.1 ASK Transmission

The ATA2745 is activated by EN = VS. VASK must remain 0V for 5 ms, then the output power can

be modulated by means of pin ASK. VEN remains equal to VS during the transmission of the

message. The ASK input activates the power amplifier and the PLL.

4.2 Take-over of the Clock Pulse in the Microcontroller

The clock of the crystal oscillator can be used for clocking the microcontroller. The ATAR090

and ATAR890 have the special feature of starting with an integrated RC oscillator to switch on

the ATA2745 with VEN = VS. 5 ms later, the 3.39-MHz clock frequency is present, so that the

message can be sent with crystal accuracy.

5. Application Circuit

The following component values are recommendations for a typical application. C4, C5, and C6

are block capacitors. The values of these capacitors depend on the board layout. C4 = 1 nF,

C5 = 1 nF, and C6 = 22 nF are typically used here. For C5, the impedance between f = 100 MHz

and f = 1 GHz should be as low as possible.

CLoop1 and CLoop2 are selected so that the antenna oscillates in resonance and the matching to

the appropriate impedance transformation is possible.

LFeed is an inductor for the antenna's DC current supply. A typical value is LFeed = 220 nH. LFeed

can be either printed on the PC board or be a discrete component.

4 ATA2745

4898B–RKE–08/06

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