Datasheet > T5753_08

T5753_08

更新时间： 2022-09-23 14:33:46

品牌	Logo	应用领域
爱特美尔 - ATMEL		/
页数	文件大小	规格书
13页	261K
描述
UHF ASK/FSK Transmitter

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T5753_08 数据手册

T5753

Figure 4-1. Tolerances of Frequency Modulation

V_S

C_Stray1

C_Stray2

L_M

C₄

XTAL

C_M

R_S

C₀

Crystal equivalent circuit

C₅

C_Switch

Using C₄= 8.2 pF ±5%, C₅= 10 pF ±5%, a switch port with C_Switch= 3 pF ±10%, stray capaci-

tances on each side of the crystal of C_Stray1= C_Stray2= 1 pF ±10%, a parallel capacitance of the

crystal of C₀= 3.2 pF ±10% and a crystal with C_M= 13 fF ±10%, an FSK deviation of ±21.5 kHz

typical with worst case tolerances of ±16.25 kHz to ±28.01 kHz results.

4.3

CLK Output

An output CLK signal is provided for a connected microcontroller, the delivered signal is CMOS

compatible if the load capacitance is lower than 10 pF.

4.3.1

Clock Pulse Take-over

The clock of the crystal oscillator can be used for clocking the microcontroller. Atmel^®’s

ATARx9x has the special feature of starting with an integrated RC-oscillator to switch on the

T5753 with ENABLE = H, and after 3 ms to assume the clock signal of the transmission IC, so

that the message can be sent with crystal accuracy.

4.3.2

Output Matching and Power Setting

The output power is set by the load impedance of the antenna. The maximum output power is

achieved with a load impedance of Z_Load,opt= (255 + j192)Ω. There must be a low resistive path

to V_Sto deliver the DC current.

The delivered current pulse of the power amplifier is 9 mA and the maximum output power is

delivered to a resistive load of 400Ω if the 1.0 pF output capacitance of the power amplifier is

compensated by the load impedance.

An optimum load impedance of:

_Load= 400Ω || j/(2 × π 1.0 pF) = (255 + j192)Ω thus results for the maximum output power of

8 dBm.

The load impedance is defined as the impedance seen from the T5753’s ANT1, ANT2 into the

matching network. Do not confuse this large signal load impedance with a small signal input

impedance delivered as input characteristic of RF amplifiers and measured from the application

into the IC instead of from the IC into the application for a power amplifier.

Less output power is achieved by lowering the real parallel part of 400Ωwhere the parallel imag-

inary part should be kept constant.

Output power measurement can be done with the circuit of Figure 4-2. Note that the component

values must be changed to compensate the individual board parasitics until the T5753 has the

right load impedance Z_Load,opt= (255 + j192)Ω. Also the damping of the cable used to measure

the output power must be calibrated out.

4510J–RKE–12/08

1 2 3 456 7 8...13

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