AX5243 datasheet(31/65 Pages) ONSEMI

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Circuit Description

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AX5243

5.8. RF Input and Output Stage (ANTP/ANTN)

The AX5243 antenna interface uses differential pins ANTP and ANTN for both RX and TX.

RX/TX switching is handled internally.

LNA

The LNA amplifies the differential RF signal from the antenna and buffers it to drive the

I/Q mixer. An external matching network is used to adapt the antenna impedance to the

IC impedance. A DC feed to GND must be provided at the antenna pins. For

recommendations, see section 7: Application Information.

In TX mode the PA drives the signal generated by the frequency generation subsystem

out to either the differential antenna terminals or to the single ended antenna pin. The

antenna terminals are chosen via the bits TXDIFF and TXSE in register

MODECFGA.

The output power of the PA is programmed via the register

TXPWRCOEFFB.

The PA can be digitally pre-distorted for high linearity.

The output amplitude can be shaped (raised cosine), this mode is selected with bit

AMPLSHAPE in register

MODECFGA. PA ramping is programmable in increments of the

bit time and can be set to 1 – 8 bit times via bits SLOWRAMP in register

MODECFGA.

Output power as well as harmonic content will depend on the external impedance seen

by the PA, recommendations are given in the section 7: Application Information.

5.9. Digital IF Channel Filter and Demodulator

The digital IF channel filter and the demodulator extract the data bit-stream from the

incoming IF signal. They must be programmed to match the modulation scheme as well

as the data-rate. Inaccurate programming will lead to loss of sensitivity.

The channel filter offers bandwidths of 995 Hz up to 221 kHz.

The AXSEM RadioLab software calculates the necessary register settings for optimal

performance and details can be found in the AX5243 Programming Manual. An overview

of the registers involved is given in the following table as reference. The register setups

typically must be done once at power-up of the device.

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