SN250 datasheet(12/130 Pages) STMICROELECTRONICS

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Top-level functional description

SN250

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Top-level functional description

Figure 2 shows a detailed block diagram of the SN250.

Figure 2.

SN250 block diagram

The radio receiver is a low-IF, super-heterodyne receiver. It utilizes differential signal paths

to minimize noise interference, and its architecture has been chosen to optimize co-

existence with other devices within the 2.4GHz band (namely, IEEE 802.11g and Bluetooth).

After amplification and mixing, the signal is filtered and combined prior to being sampled by

an ADC.

The digital receiver implements a coherent demodulator to generate a chip stream for the

hardware-based MAC. In addition, the digital receiver contains the analog radio calibration

routines and control of the gain within the receiver path.

The radio transmitter utilizes an efficient architecture in which the data stream directly

modulates the VCO. An integrated PA boosts the output power. The calibration of the TX

path as well as the output power is controlled by digital logic. If the SN250 is to be used with

an external PA, the TX_ACTIVE signal should be used to control the timing of the external

switching logic.

The integrated 4.8 GHz VCO and loop filter minimize off-chip circuitry. Only a 24MHz crystal

with its loading capacitors is required to properly establish the PLL reference signal.

The MAC interfaces the data memory to the RX and TX baseband modules. The MAC

provides hardware-based IEEE 802.15.4 packet-level filtering. It supplies an accurate

symbol time base that minimizes the synchronization effort of the software stack and meets

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