T5744-TKS 查看數據表（PDF） - Atmel Corporation

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T5744-TKS

UHF ASK/FSK Receiver

Atmel Corporation 

Figure 3. Block Diagram

CDEM

RSSI

AVCC

AGND

DGND

BR_0 BR_1

ASK-

Demodulator

and data filter

RSSI

Dem_out

RSSI IF Amp

4. Order

Data interface

Test

MIXVCC

LPF

3 MHz

IF Amp

LNAGND

LPF

3 MHz

LNA_IN

LNA

Standby logic

VCO

f

64

XTO

DATA

TEST

MODE

DVCC

ENABLE

LFGND

LFVCC

XTO

LF

T5744

RF Front End

The RF front end of the receiver is a heterodyne configuration that converts the input

signal into a 1-MHz IF signal. According to Figure 3, the front end consists of an LNA

(Low-Noise Amplifier), LO (Local Oscillator), a mixer and RF amplifier.

The LO generates the carrier frequency for the mixer via a PLL synthesizer. The XTO

(crystal oscillator) generates the reference frequency fXTO. The VCO (Voltage-Controlled

Oscillator) generates the drive voltage frequency fLO for the mixer. fLO is dependent on

the voltage at Pin LF. fLO is divided by factor 64. The divided frequency is compared to

fXTO by the phase frequency detector. The current output of the phase frequency detec-

tor is connected to a passive loop filter and thereby generates the control voltage VLF

for the VCO. By means of that configuration, VLF is controlled in a way that fLO/64 is

equal to fXTO. If fLO is determined, fXTO can be calculated using the following formula:

fXTO = fLO/64

The XTO is a one-pin oscillator that operates at the series resonance of the quartz crys-

tal. According to Figure 4, the crystal should be connected to GND via a capacitor CL.

The value of that capacitor is recommended by the crystal supplier. The value of CL

should be optimized for the individual board layout to achieve the exact value of fXTO and

hereby of fLO. When designing the system in terms of receiving bandwidth, the accuracy

of the crystal and the XTO must be considered.

3

4521B–RKE–01/03

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